LDP over RSVP Using OSPF as IGP

This chapter provides information about label distribution protocol (LDP) over resource reservation protocol with traffic engineering (RSVP-TE), also called LDP over RSVP, that uses RSVP label switched paths (LSPs) as a transport vehicle to carry the packets using LDP LSPs.

Topics in this chapter include:

Applicability

This chapter was initially written for SR OS Release 7.0.R5, but the CLI in this edition corresponds to SR OS Release 21.2.R1. There are no prerequisites.

Overview

Only user packets are tunneled over RSVP LSPs; targeted LDP (T-LDP) control messages are still sent unlabeled using the interior gateway protocol (IGP) shortest path. Because LDP does not have traffic engineering (TE), it can benefit from the RSVP-TE features. LDP fast reroute (FRR) is loopfree alternate (LFA), but with LDP over RSVP, it can use RSVP FRR detour or bypass tunnels.

The main advantage of LDP over RSVP is seen in large networks. A full mesh of intra-area RSVP LSPs between PE nodes (which in some cases is not scalable) is not needed anymore. While a label edge router (LER) may not have that many tunnels, any transit node may have thousands of LSPs, and if each transit node also has to deal with detour tunnels or bypass tunnels, this number can make the label switching router (LSR) overly burdened.

LDP over RSVP can be configured in an intra-area domain and an inter-area domain. Any router in an area can be a stitching point for LDP over RSVP. LDP over RSVP introduces a tunnel-in-tunnel tunnel type (in addition to the existing LDP tunnel type and RSVP tunnel type). If multiple tunnel types match the destination PE forwarding equivalence class (FEC) lookup, LDP prefers an LDP tunnel over an LDP over RSVP tunnel by default.

First, it is important to understand how LDP FEC resolution is working (with LDP over RSVP enabled). A more detailed description can be found later on in this chapter. The ingress LER receives an LDP label message including a FEC with prefix P and label L from a peer by a T-LDP session. LDP tries to resolve prefix P by performing a lookup in the Routing Table Manager (RTM). The result of this is a Next Hop (NH) to the destination PE, either an intra-area PE (intra-area context) or an Area Border Router (ABR) (inter-area context). When the NH matches the targeted LDP peer, LDP performs a second lookup for that NH in the tunnel table which returns a user configured RSVP LSP with the best metric. If there are multiple configured RSVP LSPs with the best metric, LDP selects the first available RSVP LSP. If all user configured RSVP LSPs are down, no more action is taken. If the user did not configure any RSVP LSPs under the T-LDP context, the lookup in the tunnel table returns the first available RSVP LSP which terminates on the ABR (inter-area) or intra-area PE with the lowest metric.

If the lookup in the tunnel table results in no RSVP LSP, the system can fall back to link-level interface LDP (iLDP). In that way, it is possible that the NH is reachable using iLDP. Accordingly, the egress label is then installed on the ingress LER.

Initial example topology shows the example topology with four PE routers and four P routers.

Figure 1. Initial example topology

OSPF area 0.0.0.1 and OSPF area 0.0.0.2 are two metro areas, connected to each other via a core area, represented by OSPF backbone area (area 0.0.0.0). Therefore, P-5, P-6, P-7, and P-8 are all acting as area border routers (ABRs). LDP over RSVP principles will be shown for intra-area PE communication (between PE-1 and PE-4) and inter-area communication (between PE-1 and PE-2).

Configuration

  1. Configuring the IP/MPLS network.

    The system addresses and IP interface addresses are configured according to Initial example topology. An interior gateway protocol (IGP) is needed to distribute routing information on all routers. In this case, the IGP is Open Shortest Path First (OSPF) using the backbone area 0.0.0.0 in the core and normal areas (area 0.0.0.1 and area 0.0.0.2) in the two metro regions, connected toward the backbone area via ABRs. A configuration example is shown for PE-1 and P-5. A similar configuration can be derived for the other P and PE nodes.

    # on PE-1:
    configure 
        router Base
            ospf 0
                traffic-engineering 
                area 0.0.0.1
                    interface "system"
                    exit
                    interface "int-PE-1-P-5"
                        interface-type point-to-point
                    exit
                exit
                no shutdown
            exit
    
    # on P-5:
    configure
        router Base
            ospf 0
                traffic-engineering
                area 0.0.0.0
                    interface "system"
                    exit
                    interface "int-P-5-P-6"
                        interface-type point-to-point
                    exit
                    interface "int-P-5-P-8"
                        interface-type point-to-point
                    exit
                exit
                area 0.0.0.1
                    interface "int-P-5-PE-1"
                        interface-type point-to-point
                    exit
                exit
                no shutdown
            exit
    

    Because Fast Reroute (FRR) will be enabled on the RSVP LSPs in the core area, Traffic Engineering (TE) is needed on the IGP. By doing this, OSPF will generate opaque link state advertisements (LSAs) which are collected in a Traffic Engineering Database (TED), separate from the traditional OSPF topology database. OSPF interfaces are set up as type point-to-point to improve convergence, no Designated Router/Backup Designated Router (DR/BDR) election process is performed. Convergence is beyond the scope of this chapter.

    On all nodes originating and terminating a T-LDP session, an explicit ldp-over-rsvp parameter must be configured to enable this OSPF instance for LDP over RSVP, as follows:

    # on PE-1, PE-2, PE-3, PE-4, P-5, P-6, P-7, P-8:
    configure
        router Base
            ospf 0
                ldp-over-rsvp
    

    To verify that OSPF neighbors are up (state: Full), the show router ospf neighbor command is executed. To check if IP interface addresses/subnets are known on all PEs, show router route-table or show router fib <IOM-card-slot> displays the content of the forwarding information base (FIB).

    *A:PE-1# show router ospf neighbor 
    
    ===============================================================================
    Rtr Base OSPFv2 Instance 0 Neighbors
    ===============================================================================
    Interface-Name                   Rtr Id          State      Pri  RetxQ   TTL
       Area-Id
    -------------------------------------------------------------------------------
    int-PE-1-P-5                     192.0.2.5       Full       1    0       36
       0.0.0.1
    -------------------------------------------------------------------------------
    No. of Neighbors: 1
    ===============================================================================
    
    *A:PE-1# show router route-table 
    
    ===============================================================================
    Route Table (Router: Base)
    ===============================================================================
    Dest Prefix[Flags]                            Type    Proto     Age        Pref
          Next Hop[Interface Name]                                    Metric 
    -------------------------------------------------------------------------------
    192.0.2.1/32                                  Local   Local     00h03m07s  0
           system                                                       0
    192.0.2.2/32                                  Remote  OSPF      00h01m18s  10
           192.168.15.2                                                 30
    192.0.2.3/32                                  Remote  OSPF      00h00m52s  10
           192.168.15.2                                                 40
    192.0.2.4/32                                  Remote  OSPF      00h00m33s  10
           192.168.15.2                                                 30
    192.0.2.5/32                                  Remote  OSPF      00h01m36s  10
           192.168.15.2                                                 10
    192.0.2.6/32                                  Remote  OSPF      00h01m18s  10
           192.168.15.2                                                 20
    192.0.2.7/32                                  Remote  OSPF      00h00m52s  10
           192.168.15.2                                                 30
    192.0.2.8/32                                  Remote  OSPF      00h00m33s  10
           192.168.15.2                                                 20
    192.168.15.0/30                               Local   Local     00h03m07s  0
           int-PE-1-P-5                                                 0
    192.168.26.0/30                               Remote  OSPF      00h01m18s  10
           192.168.15.2                                                 30
    192.168.37.0/30                               Remote  OSPF      00h00m52s  10
           192.168.15.2                                                 40
    192.168.48.0/30                               Remote  OSPF      00h00m33s  10
           192.168.15.2                                                 30
    192.168.56.0/30                               Remote  OSPF      00h01m36s  10
           192.168.15.2                                                 20
    192.168.58.0/30                               Remote  OSPF      00h01m36s  10
           192.168.15.2                                                 20
    192.168.67.0/30                               Remote  OSPF      00h01m18s  10
           192.168.15.2                                                 30
    192.168.78.0/30                               Remote  OSPF      00h00m35s  10
           192.168.15.2                                                 30
    -------------------------------------------------------------------------------
    No. of Routes: 16
    Flags: n = Number of times nexthop is repeated
           B = BGP backup route available
           L = LFA nexthop available
           S = Sticky ECMP requested
    ===============================================================================
    
    *A:PE-1# show router fib 1
    
    ===============================================================================
    FIB Display
    ===============================================================================
    Prefix [Flags]                                              Protocol
      NextHop 
    -------------------------------------------------------------------------------
    192.0.2.1/32                                                LOCAL
      192.0.2.1 (system) 
    192.0.2.2/32                                                OSPF
      192.168.15.2 (int-PE-1-P-5) 
    192.0.2.3/32                                                OSPF
      192.168.15.2 (int-PE-1-P-5) 
    192.0.2.4/32                                                OSPF
      192.168.15.2 (int-PE-1-P-5) 
    192.0.2.5/32                                                OSPF
      192.168.15.2 (int-PE-1-P-5) 
    192.0.2.6/32                                                OSPF
      192.168.15.2 (int-PE-1-P-5) 
    192.0.2.7/32                                                OSPF
      192.168.15.2 (int-PE-1-P-5) 
    192.0.2.8/32                                                OSPF
      192.168.15.2 (int-PE-1-P-5) 
    192.168.15.0/30                                             LOCAL
      192.168.15.0 (int-PE-1-P-5) 
    192.168.26.0/30                                             OSPF
      192.168.15.2 (int-PE-1-P-5) 
    192.168.37.0/30                                             OSPF
      192.168.15.2 (int-PE-1-P-5) 
    192.168.48.0/30                                             OSPF
      192.168.15.2 (int-PE-1-P-5) 
    192.168.56.0/30                                             OSPF
      192.168.15.2 (int-PE-1-P-5) 
    192.168.58.0/30                                             OSPF
      192.168.15.2 (int-PE-1-P-5) 
    192.168.67.0/30                                             OSPF
      192.168.15.2 (int-PE-1-P-5) 
    192.168.78.0/30                                             OSPF
      192.168.15.2 (int-PE-1-P-5) 
    -------------------------------------------------------------------------------
    Total Entries : 16
    -------------------------------------------------------------------------------
    ==============================================================================
    

    The next step in the process of setting up the IP/MPLS network, is enabling the IP interfaces in the MPLS and rsvp context on all involved nodes (PE and P nodes). By default, the system interface is put automatically within the MPLS/rsvp context. When an interface is put in the mpls context, the system also copies it into the rsvp context. Explicit enabling of MPLS and rsvp context is done by the no shutdown command. The following output displays the MPLS/RSVP configuration for PE-1.

    # on PE-1:
    configure
        router Base
            mpls
                interface "int-PE-1-P-5"
                exit
                no shutdown
            exit
            rsvp
                no shutdown
            exit
    
  2. Configure the RSVP LSPs.

    In both metro areas, RSVP LSPs are set up from all PEs toward the ABRs, no intra-area PE-PE RSVP LSPs are needed. In the core/backbone, a full RSVP LSP mesh is required. To simplify the RSVP LSP configuration, no FRR is enabled on the RSVP LSPs in the metro areas, only in the backbone area. All RSVP paths are configured as strict paths. As an example, the configuration for PE-1 and P-5 is as follows:

    
    # on PE-1:
    configure 
        router Base
            mpls
                path "path-PE-1-P-5"
                    hop 10 192.168.15.2 strict
                    no shutdown
                exit
                path "path-PE-1-P-5-P-8"
                    hop 10 192.168.15.2 strict
                    hop 20 192.168.58.2 strict
                    no shutdown
                exit
                lsp "LSP-PE-1-P-5"
                    to 192.0.2.5
                    primary "path-PE-1-P-5"
                    exit
                    no shutdown
                exit
                lsp "LSP-PE-1-P-8"
                    to 192.0.2.8
                    primary "path-PE-1-P-5-P-8"
                    exit
                    no shutdown
                exit
    
    # on P-5:
    configure
        router Base
            mpls
                path "path-P-5-P-6"
                    hop 10 192.168.56.2 strict
                    no shutdown
                exit
                path "path-P-5-P-8"
                    hop 10 192.168.58.2 strict
                    no shutdown
                exit
                path "path-P-5-P-6-P-7"
                    hop 10 192.168.56.2 strict
                    hop 20 192.168.67.2 strict
                    no shutdown
                exit
                path "path-P-5-PE-1"
                    hop 10 192.168.15.1 strict
                    no shutdown
                exit
                path "path-P-5-P-8-PE-4"
                    hop 10 192.168.58.2 strict
                    hop 20 192.168.48.1 strict
                    no shutdown
                exit
                lsp "LSP-P-5-PE-1"
                    to 192.0.2.1
                    primary "path-P-5-PE-1"
                    exit
                    no shutdown
                exit
                lsp "LSP-P-5-PE-4"
                    to 192.0.2.4
                    primary "path-P-5-P-8-PE-4"
                    exit
                    no shutdown
                exit
                lsp "LSP-P-5-P-6"
                    to 192.0.2.6
                    path-computation-method local-cspf
                    fast-reroute facility
                    exit
                    primary "path-P-5-P-6"
                    exit
                    no shutdown
                exit
                lsp "LSP-P-5-P-7"
                    to 192.0.2.7
                    path-computation-method local-cspf
                    fast-reroute facility
                    exit
                    primary "path-P-5-P-6-P-7"
                    exit
                    no shutdown
                exit
                lsp "LSP-P-5-P-8"
                    to 192.0.2.8
                    path-computation-method local-cspf
                    fast-reroute facility
                    exit
                    primary "path-P-5-P-8"
                    exit
                    no shutdown
                exit
    

    The following command on PE-1 lists the RSVP LSPs:

    *A:PE-1# show router mpls lsp 
     
    ===============================================================================
    MPLS LSPs (Originating)
    ===============================================================================
    LSP Name                                            Tun     Fastfail  Adm  Opr
      To                                                Id      Config 
    -------------------------------------------------------------------------------
    LSP-PE-1-P-5                                        1       No        Up   Up
      192.0.2.5 
    LSP-PE-1-P-8                                        2       No        Up   Up
      192.0.2.8 
    -------------------------------------------------------------------------------
    LSPs : 2
    ===============================================================================
    

    The following command on PE-1 shows the tunnel table for the RSVP signaling protocol. By default, RSVP LSPs have preference 7.

    *A:PE-1# show router tunnel-table
     
    ===============================================================================
    IPv4 Tunnel Table (Router: Base)
    ===============================================================================
    Destination           Owner     Encap TunnelId  Pref   Nexthop        Metric
       Color 
    -------------------------------------------------------------------------------
    192.0.2.5/32          rsvp      MPLS  1         7      192.168.15.2   16777215
    192.0.2.8/32          rsvp      MPLS  2         7      192.168.15.2   16777215
    -------------------------------------------------------------------------------
    Flags: B = BGP or MPLS backup hop available
           L = Loop-Free Alternate (LFA) hop available
           E = Inactive best-external BGP route
           k = RIB-API or Forwarding Policy backup hop
    ===============================================================================
    

    On ABR P-5:

    *A:P-5# show router mpls lsp 
    
    ===============================================================================
    MPLS LSPs (Originating)
    ===============================================================================
    LSP Name                                            Tun     Fastfail  Adm  Opr
      To                                                Id      Config 
    -------------------------------------------------------------------------------
    LSP-P-5-PE-1                                        1       No        Up   Up
      192.0.2.1 
    LSP-P-5-PE-4                                        2       No        Up   Up
      192.0.2.4 
    LSP-P-5-P-6                                         3       Yes       Up   Up
      192.0.2.6 
    LSP-P-5-P-7                                         4       Yes       Up   Up
      192.0.2.7 
    LSP-P-5-P-8                                         5       Yes       Up   Up
      192.0.2.8 
    -------------------------------------------------------------------------------
    LSPs : 5
    ==============================================================================
    
    *A:P-5# show router tunnel-table 
    
    ===============================================================================
    IPv4 Tunnel Table (Router: Base)
    ===============================================================================
    Destination           Owner     Encap TunnelId  Pref   Nexthop        Metric
       Color 
    ------------------------------------------------------------------------------
    192.0.2.1/32          rsvp      MPLS  1         7      192.168.15.1   16777215
    192.0.2.4/32          rsvp      MPLS  2         7      192.168.58.2   16777215
    192.0.2.6/32 [B]      rsvp      MPLS  3         7      192.168.56.2   10
    192.0.2.7/32 [B]      rsvp      MPLS  4         7      192.168.56.2   20
    192.0.2.8/32 [B]      rsvp      MPLS  5         7      192.168.58.2   10
    -------------------------------------------------------------------------------
    Flags: B = BGP or MPLS backup hop available
           L = Loop-Free Alternate (LFA) hop available
           E = Inactive best-external BGP route
           k = RIB-API or Forwarding Policy backup hop
    ===============================================================================
    

    By default, the metric for strict LSPs configured without Constrained Shortest Path First (CSPF) (RSVP LSPs in metro areas) is infinite (value = 16777215). The LSP metric for CSPF LSPs (RSVP LSPs in the core area) follows the IGP cost. LSP metrics can be explicitly set on the LSP level, see also in the Additional topics section.

    *A:PE-1# configure router mpls lsp "LSP-PE-1-P-5" metric ?
      - metric <metric>
      - no metric
    
     <metric>             : <0..16777215>
    

    Whenever an RSVP LSP comes up, it is by default eligible for LDP over RSVP, meaning that RSVP signals to the relevant IGP (OSPF in this case) that the LSP should be included in the IGP Shortest Path First (SPF) run. The destination of the LSP (192.0.2.5) is considered as a potential endpoint in the Forwarding Equivalence Class (FEC) resolution. With the info detail command, all default settings of a context are shown.

    *A:PE-1# configure router mpls lsp "LSP-PE-1-P-5"
    *A:PE-1>config>router>mpls>lsp# info detail 
    ----------------------------------------------
                    to 192.0.2.5
                    rsvp-resv-style se
                    adaptive
                    no auto-bandwidth
                    no path-computation-method
                    metric-type igp
                    no fallback-path-computation-method
                    no include 
                    no exclude
                    no propagate-admin-group
                    no adspec
                    entropy-label inherit
                    no fast-reroute
                    hop-limit 255
                    retry-limit 0
                    retry-timer 30
                    no least-fill
                    no metric
                    pce-report inherit
                    no pce-control
                    ldp-over-rsvp include
                    vprn-auto-bind include
                    igp-shortcut
                    bgp-shortcut
                    bgp-transport-tunnel include
                    class-type 0
                    main-ct-retry-limit 0
                    no revert-timer
                    no load-balancing-weight
                    no class-forwarding
                    lsp-self-ping inherit
                    bfd
                        no bfd-template
                        lsp-ping-interval 60
                        no bfd-enable
                        no failure-action
                        wait-for-up-timer 4
                    exit
                    primary "path-PE-1-P-5"
                        no hop-limit
                        no adaptive
                        no include
                        no exclude
                        record
                        record-label
                        no bandwidth
                        priority 7 0
                        no class-type
                        no backup-class-type
                        bfd
                            no bfd-template
                            lsp-ping-interval 60
                            no bfd-enable
                            wait-for-up-timer 4
                        exit
                        no shutdown
                    exit
                    no shutdown
    ----------------------------------------------
    
    *A:PE-1# show router mpls lsp "LSP-PE-1-P-5" detail 
    
    ===============================================================================
    MPLS LSPs (Originating) (Detail)
    ===============================================================================
    Legend : 
        + - Inherited
    ===============================================================================
    -------------------------------------------------------------------------------
    Type : Originating 
    -------------------------------------------------------------------------------
    LSP Name   : LSP-PE-1-P-5
    LSP Type        : RegularLsp                LSP Tunnel ID        : 1
    LSP Index       : 1                         TTM Tunnel Id        : 1
    From            : 192.0.2.1
    To              : 192.0.2.5
    Adm State       : Up                        Oper State           : Up
    LSP Up Time     : 0d 00:10:37               LSP Down Time        : 0d 00:00:00
    Transitions     : 1                         Path Changes         : 1
    Retry Limit     : 0                         Retry Timer          : 30 sec
    Signaling       : RSVP                      Resv. Style          : SE
    Hop Limit       : 255                       Negotiated MTU       : 1564
    Adaptive        : Enabled                   ClassType            : 0
    FastReroute     : Disabled                  Oper FR              : Disabled
    PathCompMethod  : none                      ADSPEC               : Disabled
    FallbkPathComp  : not-applicable 
    Metric          : N/A 
    Load Bal Wt     : N/A                       ClassForwarding      : Disabled
    Include Grps    :                           Exclude Grps         : 
    None                                           None
    Least Fill      : Disabled 
    BFD Template    : None                      BFD Ping Intvl       : 60
    BFD Enable      : False                     BFD Failure-action   : None 
    WaitForUpTimer  : 4 
    
    Revert Timer    : Disabled                  Next Revert In       : N/A
    Entropy Label   : Enabled+                  Oper Entropy Label   : Enabled
    Negotiated EL   : Disabled 
    Auto BW         : Disabled 
    LdpOverRsvp     : Enabled
    VprnAutoBind    : Enabled 
    IGP Shortcut    : Enabled                   BGP Shortcut         : Enabled
    IGP LFA         : Disabled                  IGP Rel Metric       : Disabled
    BGPTransTun     : Enabled 
    Oper Metric     : 16777215 
    Prop Adm Grp    : Disabled 
    PCE Report      : Disabled+ 
    PCE Control     : Disabled 
    Path Profile    : None 
    Admin Tags      : None 
    Lsp Self Ping   : Disabled+                 Self Ping Timeouts   : 0
    SelfPingOAMFail*: 0 
    
    Primary(a)      : path-PE-1-P-5
                                                Up Time              : 0d 00:10:37
    Bandwidth       : 0 Mbps 
    ===============================================================================
    * indicates that the corresponding row element may have been truncated.
    

    The following command makes a specific RSVP LSP ineligible for LDP over RSVP:

    # on PE-1:
    configure 
        router Base 
            mpls 
                lsp <LSP-name> 
                    ldp-over-rsvp exclude
    
  3. Create T-LDP sessions according to RSVP LSPs.

    It is a must that when configuring an RSVP LSP eligible for LDP over RSVP, also a T-LDP session is initiated. This must be done on all PE and P nodes.

    # on PE-1:
    configure
        router Base
            ldp
                targeted-session
                    peer 192.0.2.5
                    exit
                    peer 192.0.2.8
                    exit
                exit
    
    *A:PE-1# show router ldp session ipv4
     
    ==============================================================================
    LDP IPv4 Sessions
    ==============================================================================
    Peer LDP Id         Adj Type  State         Msg Sent  Msg Recv  Up Time
    ------------------------------------------------------------------------------
    192.0.2.5:0         Targeted  Established   17        18        0d 00:01:05
    192.0.2.8:0         Targeted  Established   10        11        0d 00:00:23
    ------------------------------------------------------------------------------
    No. of IPv4 Sessions: 2
    =============================================================================
    
  4. Enable LDP over RSVP.

    This is done using the tunneling keyword inside the T-LDP session context. This configuration is needed on all PE and ABR nodes.

    # on PE-1:
    configure 
        router Base
            ldp
                targeted-session
                    peer 192.0.2.5
                        tunneling
                        exit
                    exit
                    peer 192.0.2.8
                        tunneling
                        exit
                    exit
                exit
    

    As a result of the tunneling command, the LDP over RSVP process of FEC resolving is initiated. As already stated in the introduction, FEC resolution is a three-step process. First run an SPF calculation to the destination, then select an endpoint close to that destination followed by a tunnel to that endpoint. The next two steps go more into detail on this FEC resolution process. Step 5 will handle inter-area FEC resolving and Step 6 will handle intra-area FEC resolving.

  5. Inter-area FEC resolving (ingress LER is PE-1, egress LER is PE-2)

    1. Verification endpoint nodes and associated RSVP tunnels.

      The first thing to do in the inter-area FEC resolving process is for PE-1 to perform an SPF calculation toward PE-2 with the purpose to search for an eligible endpoint, as close as possible to PE-2. An endpoint is eligible when:

      • a T-LDP session exists between PE-1 and the endpoint node

      • tunneling is configured on the endpoint node

      • PE-1 received a label for the destination FEC from the endpoint

      • and an RSVP LSP that can be used for LDP over RSVP exists between PE-1 and the endpoint node

      Endpoint node in OSPF area 1 can be either P-5 or P-8 (only those nodes have a T-LDP session toward PE-1). The following command shows that P-5 is the endpoint node (EgrNextHop). The RSVP LSP that is used has ID 1.

      *A:PE-1# show router ldp bindings active prefixes prefix 192.0.2.2/32  
      
      ===============================================================================
      LDP Bindings (IPv4 LSR ID 192.0.2.1)
                   (IPv6 LSR ID ::)
      ===============================================================================
      Label Status:
              U - Label In Use, N - Label Not In Use, W - Label Withdrawn
              WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route
              e - Label ELC
      FEC Flags:
              LF - Lower FEC, UF - Upper FEC, M - Community Mismatch,
              BA - ASBR Backup FEC
              (S) - Static           (M) - Multi-homed Secondary Support
              (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route
              (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop
              (C) - FEC resolved with class-based-forwarding
      ===============================================================================
      LDP IPv4 Prefix Bindings (Active)
      ===============================================================================
      Prefix                                      Op
      IngLbl                                      EgrLbl
      EgrNextHop                                  EgrIf/LspId
      -------------------------------------------------------------------------------
      192.0.2.2/32                                Push
        --                                        524268
      192.0.2.5                                   LspId 1
      
      192.0.2.2/32                                Swap
      524281                                      524268
      192.0.2.5                                   LspId 1
      
      -------------------------------------------------------------------------------
      No. of IPv4 Prefix Active Bindings: 2
      ===============================================================================
      

      The following command shows that RSVP LSP with ID 1 is LSP-PE-1-P-5:

      *A:PE-1# show router mpls lsp 
      
      ===============================================================================
      MPLS LSPs (Originating)
      ===============================================================================
      LSP Name                                            Tun     Fastfail  Adm  Opr
        To                                                Id      Config 
      -------------------------------------------------------------------------------
      LSP-PE-1-P-5                                        1       No        Up   Up
        192.0.2.5 
      LSP-PE-1-P-8                                        2       No        Up   Up
        192.0.2.8 
      -------------------------------------------------------------------------------
      LSPs : 2
      ===============================================================================
      

      The following command shows that the RSVP tunnel toward P-5 has tunnel ID 1 and next-hop 192.168.15.2:

      *A:PE-1# show router tunnel-table 
      
      ===============================================================================
      IPv4 Tunnel Table (Router: Base)
      ==============================================================================
      Destination           Owner     Encap TunnelId  Pref   Nexthop        Metric
         Color 
      -------------------------------------------------------------------------------
      192.0.2.2/32          ldp       MPLS  65540     9      192.0.2.5      30
      192.0.2.3/32          ldp       MPLS  65541     9      192.0.2.5      40
      192.0.2.4/32          ldp       MPLS  65538     9      192.0.2.5      30
      192.0.2.5/32          rsvp      MPLS  1         7      192.168.15.2   16777215
      192.0.2.5/32          ldp       MPLS  65537     9      192.0.2.5      10
      192.0.2.6/32          ldp       MPLS  65539     9      192.0.2.5      20
      192.0.2.7/32          ldp       MPLS  65542     9      192.0.2.5      30
      192.0.2.8/32          rsvp      MPLS  2         7      192.168.15.2   16777215
      192.0.2.8/32          ldp       MPLS  65543     9      192.0.2.8      20
      -------------------------------------------------------------------------------
      Flags: B = BGP or MPLS backup hop available
             L = Loop-Free Alternate (LFA) hop available
             E = Inactive best-external BGP route
             k = RIB-API or Forwarding Policy backup hop
      ===============================================================================
      

      Endpoint node in OSPF area 0 can be either P-6, P-7, or P-8 (only those nodes have a T-LDP session toward P-5). The following command on P-5 shows that P-6 is the endpoint node (EgrNextHop). The RSVP LSP that is used on P-5 has ID 3.

      *A:P-5# show router ldp bindings active prefixes prefix 192.0.2.2/32 
      
      ===============================================================================
      LDP Bindings (IPv4 LSR ID 192.0.2.5)
                   (IPv6 LSR ID ::)
      ===============================================================================
      Label Status:
              U - Label In Use, N - Label Not In Use, W - Label Withdrawn
              WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route
              e - Label ELC
      FEC Flags:
              LF - Lower FEC, UF - Upper FEC, M - Community Mismatch,
              BA - ASBR Backup FEC
              (S) - Static           (M) - Multi-homed Secondary Support
              (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route
              (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop 
              (C) - FEC resolved with class-based-forwarding
      ===============================================================================
      LDP IPv4 Prefix Bindings (Active)
      ===============================================================================
      Prefix                                      Op
      IngLbl                                      EgrLbl
      EgrNextHop                                  EgrIf/LspId
      -------------------------------------------------------------------------------
      192.0.2.2/32                                Push
        --                                        524270
      192.0.2.6                                   LspId 3
      
      192.0.2.2/32                                Swap
      524268                                      524270
      192.0.2.6                                   LspId 3
      
      -------------------------------------------------------------------------------
      No. of IPv4 Prefix Active Bindings: 2
      ===============================================================================
      

      The following command shows that the RSVP LSP with ID 3 is LSP-P-5-P-6:

      *A:P-5# show router mpls lsp 
      
      ===============================================================================
      MPLS LSPs (Originating)
      ===============================================================================
      LSP Name                                            Tun     Fastfail  Adm  Opr
        To                                                Id      Config 
      -------------------------------------------------------------------------------
      LSP-P-5-PE-1                                        1       No        Up   Up
        192.0.2.1 
      LSP-P-5-PE-4                                        2       No        Up   Up
        192.0.2.4 
      LSP-P-5-P-6                                         3       Yes       Up   Up
        192.0.2.6
      LSP-P-5-P-7                                         4       Yes       Up   Up
        192.0.2.7 
      LSP-P-5-P-8                                         5       Yes       Up   Up
        192.0.2.8 
      -------------------------------------------------------------------------------
      LSPs : 5
      ===============================================================================
      

      The following command shows that the RSVP tunnel with ID 3 and destination 192.0.2.6 has next-hop 192.168.56.2 and metric 10:

      *A:P-5# show router tunnel-table 
      
      ===============================================================================
      IPv4 Tunnel Table (Router: Base)
      ===============================================================================
      Destination           Owner     Encap TunnelId  Pref   Nexthop        Metric
         Color 
      -------------------------------------------------------------------------------
      192.0.2.1/32          rsvp      MPLS  1         7      192.168.15.1   16777215
      192.0.2.1/32          ldp       MPLS  65537     9      192.0.2.1      10
      192.0.2.2/32          ldp       MPLS  65540     9      192.0.2.6      20
      192.0.2.3/32          ldp       MPLS  65541     9      192.0.2.7      30
      192.0.2.4/32          rsvp      MPLS  2         7      192.168.58.2   16777215
      192.0.2.4/32          ldp       MPLS  65538     9      192.0.2.4      20
      192.0.2.6/32 [B]      rsvp      MPLS  3         7      192.168.56.2   10
      192.0.2.6/32          ldp       MPLS  65539     9      192.0.2.6      10
      192.0.2.7/32 [B]      rsvp      MPLS  4         7      192.168.56.2   20
      192.0.2.7/32          ldp       MPLS  65542     9      192.0.2.7      20
      192.0.2.8/32 [B]      rsvp      MPLS  5         7      192.168.58.2   10
      192.0.2.8/32          ldp       MPLS  65543     9      192.0.2.8      10
      -------------------------------------------------------------------------------
      Flags: B = BGP or MPLS backup hop available
             L = Loop-Free Alternate (LFA) hop available
             E = Inactive best-external BGP route
             k = RIB-API or Forwarding Policy backup hop
      ===============================================================================
      

      On node P-6, the following commands are launched for the final destination node PE-2. Also there, an RSVP LSP toward PE-2 is used as transport tunnel for user packets.

      *A:P-6# show router ldp bindings active prefixes prefix 192.0.2.2/32 
      
      ===============================================================================
      LDP Bindings (IPv4 LSR ID 192.0.2.6)
                   (IPv6 LSR ID ::)
      ===============================================================================
      Label Status:
              U - Label In Use, N - Label Not In Use, W - Label Withdrawn
              WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route
              e - Label ELC 
      FEC Flags:
              LF - Lower FEC, UF - Upper FEC, M - Community Mismatch,
              BA - ASBR Backup FEC
              (S) - Static           (M) - Multi-homed Secondary Support
              (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route
              (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop
              (C) - FEC resolved with class-based-forwarding
      ===============================================================================
      LDP IPv4 Prefix Bindings (Active)
      ===============================================================================
      Prefix                                      Op
      IngLbl                                      EgrLbl
      EgrNextHop                                  EgrIf/LspId
      -------------------------------------------------------------------------------
      192.0.2.2/32                                Push
        --                                        524285
      192.0.2.2                                   LspId 1
      
      192.0.2.2/32                                Swap
      524270                                      524285
      192.0.2.2                                   LspId 1
      
      -------------------------------------------------------------------------------
      No. of IPv4 Prefix Active Bindings: 2
      ===============================================================================
      
      *A:P-6# show router mpls lsp 
      
      ===============================================================================
      MPLS LSPs (Originating)
      ===============================================================================
      LSP Name                                            Tun     Fastfail  Adm  Opr
        To                                                Id      Config 
      -------------------------------------------------------------------------------
      LSP-P-6-PE-2                                        1       No        Up   Up
        192.0.2.2
      LSP-P-6-PE-3                                        2       No        Up   Up 
        192.0.2.3                                                                 
      LSP-P-6-P-5                                         3       Yes       Up   Up 
        192.0.2.5                                                                 
      LSP-P-6-P-7                                         4       Yes       Up   Up 
        192.0.2.7                                                                 
      LSP-P-6-P-8                                         5       Yes       Up   Up 
        192.0.2.8                                                                 
      ------------------------------------------------------------------------------- 
      LSPs : 5 
      =============================================================================== 
      
      *A:P-6# show router tunnel-table  
      
      =============================================================================== 
      IPv4 Tunnel Table (Router: Base) 
      =============================================================================== 
      Destination           Owner     Encap TunnelId  Pref   Nexthop        Metric 
         Color                                                               
      ------------------------------------------------------------------------------- 
      192.0.2.1/32          ldp       MPLS  65539     9      192.0.2.5      20 
      192.0.2.2/32          rsvp      MPLS  1         7      192.168.26.1   16777215
      192.0.2.2/32          ldp       MPLS  65537     9      192.0.2.2      10 
      192.0.2.3/32          rsvp      MPLS  2         7      192.168.67.2   16777215 
      192.0.2.3/32          ldp       MPLS  65538     9      192.0.2.3      20 
      192.0.2.4/32          ldp       MPLS  65542     9      192.0.2.8      30 
      192.0.2.5/32 [B]      rsvp      MPLS  3         7      192.168.56.1   10 
      192.0.2.5/32          ldp       MPLS  65540     9      192.0.2.5      10 
      192.0.2.7/32 [B]      rsvp      MPLS  4         7      192.168.67.2   10 
      192.0.2.7/32          ldp       MPLS  65541     9      192.0.2.7      10 
      192.0.2.8/32 [B]      rsvp      MPLS  5         7      192.168.67.2   20 
      192.0.2.8/32          ldp       MPLS  65543     9      192.0.2.8      20 
      ------------------------------------------------------------------------------- 
      Flags: B = BGP or MPLS backup hop available 
             L = Loop-Free Alternate (LFA) hop available 
             E = Inactive best-external BGP route 
             k = RIB-API or Forwarding Policy backup hop 
      =============================================================================== 
      

      Nodes P-5 and P-6 behave as stitching nodes to stitch RSVP LSPs. P-5 stitches LSP-PE-1-P-5 and LSP-P-5-P-6 together while P-6 node stitches LSP-P-5-P-6 and LSP-P-6-PE-2 together.

      When the endpoints are defined, one corresponding RSVP LSP to those endpoints is chosen (when ECMP equals 1). Selection criteria are as follows. When RSVP LSPs are configured under the T-LDP tunneling command (maximum 4), the one with the lowest LSP metric is selected. When no RSVP LSPs are configured under the T-LDP tunneling command, LDP checks the tunnel table for all available RSVP LSPs. The RSVP LSP with the lowest metric and operational state up is selected.

    2. Traffic verification using a virtual private routed network (VPRN) service.

      Figure 2. VPRN 1 with LDP over RSVP and no intra-area PE connectivity

      VPRN service 1 is set up between three PE nodes (PE-1, PE-2, and PE-4) using the auto-bind-tunnel resolution-filter ldp resolution filter command. See also VPRN 1 with LDP over RSVP and no intra-area PE connectivity for the exact addressing scheme.

      # on PE-1:
      configure
          service 
              vprn 1 name "VPRN 1" customer 1 create 
                  autonomous-system 64496
                  interface "int-PE-1-CE-1" create
                      address 172.16.1.1/30
                      sap 1/1/4:1 create
                      exit
                  exit
                  static-route-entry 10.0.1.0/24
                      next-hop 172.16.1.2
                          no shutdown
                      exit
                  exit
                  bgp-ipvpn
                      mpls
                          auto-bind-tunnel
                              resolution-filter
                                  ldp
                              exit
                              resolution filter
                          exit
                          route-distinguisher 64496:1
                          vrf-target target:64496:1
                          no shutdown
                      exit
                  exit
                  no shutdown
      

      In order to distribute VPRN information (VPN-IPv4 routes and VPRN service labels) across the service provider network, Multi-Protocol Border Gateway Protocol (MP-BGP) is needed. MP-BGP is configured on PE-1, PE-2, and PE-4 with P-5 (192.0.2.5) being the Route Reflector (RR). In this way, no full BGP mesh between the three PE-nodes is needed, only a BGP peering toward RR.

      # on PE-1:
      configure 
          router Base
              autonomous-system 64496
              bgp
                  group "internal"
                      family ipv4 vpn-ipv4
                      peer-as 64496
                      neighbor 192.0.2.5
                      exit
                  exit
                  no shutdown
      
      # on P-5:
      configure 
          router Base
              autonomous-system 64496
              bgp
                  group "internal"
                      family ipv4 vpn-ipv4
                      peer-as 64496
                      cluster 5.5.5.5
                      neighbor 192.0.2.1
                      exit
                      neighbor 192.0.2.2
                      exit
                      neighbor 192.0.2.4
                      exit
                  exit
                  no shutdown
      

      If user traffic is monitored between PE-1 (ingress LER) and PE-2 (egress LER), three labels are seen. The outer label is the transport label distributed using the RSVP protocol, the inner label is the service label distributed using MP-BGP. LDP over RSVP adds an extra MPLS transport label between the outer transport and the service label (distributed using LDP). This middle label is used to tell the endpoint nodes (P-5 and P-6 acting as ABR) what to do. The transport label stack contains two labels: an RSVP label and an LDP label.

      The following command shows that RSVP transport label 524287 is added as the outer label on each user packet sent on the link from PE-1 to P-5:

      *A:PE-1# show router rsvp session lsp-name "LSP-PE-1-P-5::path-PE-1-P-5" detail  
      
      =============================================================================== 
      RSVP Sessions (Detailed) 
      =============================================================================== 
      ------------------------------------------------------------------------------- 
      LSP : LSP-PE-1-P-5::path-PE-1-P-5 
      ------------------------------------------------------------------------------- 
      From            : 192.0.2.1             To             : 192.0.2.5 
      Tunnel ID       : 1                     LSP ID         : 37888 
      Style           : SE                    State          : Up 
      Session Type    : Originate              
      In Interface    : n/a                   Out Interface  : 1/1/1 
      In IF Name      : n/a                    
      Out IF Name     : int-PE-1-P-5           
      In Label        : n/a                   Out Label      : 524287
      Previous Hop    : n/a                   Next Hop       : 192.168.15.2 
      Hops            :                        
                        192.168.15.2(S) 
      SetupPriority   : 7                     Hold Priority  : 0 
      Class Type      : 0                      
      SubGrpOrig ID   : 0                     SubGrpOrig Addr:  
      P2MP ID         : 0                      
      FrrAvailType    : N/A                    
      FrrSrlgStrict   : N/A                   SrlgDisjoint   : N/A 
      
      Path Recd       : 0                     Path Sent      : 57 
      Resv Recd       : 59                    Resv Sent      : 0 
      Summary msgs    :                        
      SPath Recd      : 0                     SPath Sent     : 0 
      SResv Recd      : 0                     SResv Sent     : 0 
      LSP Attr Flags  : N/A                    
      =============================================================================== 
      

      The following command shows that LDP label 524268 is added as the middle label on each user packet:

      *A:PE-1# show router ldp bindings active prefixes prefix 192.0.2.2/32  
      
      =============================================================================== 
      LDP Bindings (IPv4 LSR ID 192.0.2.1) 
                   (IPv6 LSR ID ::) 
      =============================================================================== 
      Label Status: 
              U - Label In Use, N - Label Not In Use, W - Label Withdrawn 
              WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route 
              e - Label ELC 
      FEC Flags: 
              LF - Lower FEC, UF - Upper FEC, M - Community Mismatch, 
              BA - ASBR Backup FEC 
              (S) - Static           (M) - Multi-homed Secondary Support 
              (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route 
              (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop 
              (C) - FEC resolved with class-based-forwarding 
      =============================================================================== 
      LDP IPv4 Prefix Bindings (Active) 
      =============================================================================== 
      Prefix                                      Op 
      IngLbl                                      EgrLbl 
      EgrNextHop                                  EgrIf/LspId 
      ------------------------------------------------------------------------------- 
      192.0.2.2/32                                Push 
        --                                        524268
      192.0.2.5                                   LspId 1 
      
      192.0.2.2/32                                Swap 
      524281                                      524268
      192.0.2.5                                   LspId 1 
      
      ------------------------------------------------------------------------------- 
      No. of IPv4 Prefix Active Bindings: 2 
      =============================================================================== 
      

      Service label 524277 is added as the inner MP-BGP label on each user packet.

      Note:

      This label will not change at endpoint nodes (P-5 and P-6). Ingress LER (PE-1) will push the service label to the user packet while the egress LER (PE-2) will pop the service label.

      *A:PE-1# show router bgp neighbor 192.0.2.5 received-routes vpn-ipv4  
      =============================================================================== 
       BGP Router ID:192.0.2.1        AS:64496       Local AS:64496       
      =============================================================================== 
       Legend - 
       Status codes  : u - used, s - suppressed, h - history, d - decayed, * - valid 
                       l - leaked, x - stale, > - best, b - backup, p - purge 
       Origin codes  : i - IGP, e - EGP, ? - incomplete 
      
      =============================================================================== 
      BGP VPN-IPv4 Routes 
      =============================================================================== 
      Flag  Network                                            LocalPref   MED 
            Nexthop (Router)                                   Path-Id     IGP Cost 
            As-Path                                                        Label 
      ------------------------------------------------------------------------------- 
      i     64496:1:10.0.1.0/24                                100         None 
            192.0.2.1                                          None        0 
            No As-Path                                                     524277 
      u*>i  64496:1:10.0.2.0/24                                100         None 
            192.0.2.2                                          None        30 
            No As-Path                                                     524277 
      u*>i  64496:1:10.0.4.0/24                                100         None 
            192.0.2.4                                          None        30 
            No As-Path                                                     524277 
      i     64496:1:172.16.1.0/30                              100         None 
            192.0.2.1                                          None        0 
            No As-Path                                                     524277 
      u*>i  64496:1:172.16.2.0/30                              100         None 
            192.0.2.2                                          None        30 
            No As-Path                                                     524277 
      u*>i  64496:1:172.16.4.0/30                              100         None 
            192.0.2.4                                          None        30 
            No As-Path                                                     524277 
      ------------------------------------------------------------------------------- 
      Routes : 6 
      =============================================================================== 
      

      The following command shows that RSVP transport label 524284 is added as the top label on each user packet for traffic sent from P-5 to P-6:

      *A:P-5# show router rsvp session lsp-name "LSP-P-5-P-6::path-P-5-P-6" detail  
      
      =============================================================================== 
      RSVP Sessions (Detailed) 
      =============================================================================== 
      ------------------------------------------------------------------------------- 
      LSP : LSP-P-5-P-6::path-P-5-P-6 
      ------------------------------------------------------------------------------- 
      From            : 192.0.2.5             To             : 192.0.2.6 
      Tunnel ID       : 3                     LSP ID         : 19968 
      Style           : SE                    State          : Up 
      Session Type    : Originate              
      In Interface    : n/a                   Out Interface  : 1/1/1 
      In IF Name      : n/a                    
      Out IF Name     : int-P-5-P-6            
      In Label        : n/a                   Out Label      : 524284
      Previous Hop    : n/a                   Next Hop       : 192.168.56.2 
      Hops            :                        
                        192.168.56.2(S) 
      SetupPriority   : 7                     Hold Priority  : 0 
      Class Type      : 0                      
      SubGrpOrig ID   : 0                     SubGrpOrig Addr:  
      P2MP ID         : 0                      
      FrrAvailType    : Facility               
      FrrBypassLspName: bypass-link192.168.56.2-61441 
      FrrSrlgStrict   : N/A                   SrlgDisjoint   : N/A 
      
      Path Recd       : 0                     Path Sent      : 62 
      Resv Recd       : 58                    Resv Sent      : 0 
      Summary msgs    :                        
      SPath Recd      : 0                     SPath Sent     : 0 
      SResv Recd      : 0                     SResv Sent     : 0 
      LSP Attr Flags  : N/A                    
      =============================================================================== 
      

      LDP label 524270 is added as the middle label on each user packet.

      *A:P-5# show router ldp bindings active prefixes prefix 192.0.2.2/32  
      
      =============================================================================== 
      LDP Bindings (IPv4 LSR ID 192.0.2.5) 
                   (IPv6 LSR ID ::) 
      =============================================================================== 
      Label Status: 
              U - Label In Use, N - Label Not In Use, W - Label Withdrawn 
              WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route 
              e - Label ELC 
      FEC Flags: 
              LF - Lower FEC, UF - Upper FEC, M - Community Mismatch, 
              BA - ASBR Backup FEC 
              (S) - Static           (M) - Multi-homed Secondary Support 
              (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route 
              (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop 
              (C) - FEC resolved with class-based-forwarding 
      =============================================================================== 
      LDP IPv4 Prefix Bindings (Active) 
      =============================================================================== 
      Prefix                                      Op 
      IngLbl                                      EgrLbl 
      EgrNextHop                                  EgrIf/LspId 
      ------------------------------------------------------------------------------- 
      192.0.2.2/32                                Push 
        --                                        524270 
      192.0.2.6                                   LspId 3 
      
      192.0.2.2/32                                Swap 
      524268                                      524270
      192.0.2.6                                   LspId 3 
      
      ------------------------------------------------------------------------------- 
      No. of IPv4 Prefix Active Bindings: 2 
      =============================================================================== 
      

      Service label 524277 is added as the inner MP-BGP label on each user packet.

      The following command shows that RSVP transport label 524287 is added as the outer label on each user packet sent from P-6 to PE-2.

      *A:P-6# show router rsvp session lsp-name "LSP-P-6-PE-2::path-P-6-PE-2" detail  
      
      =============================================================================== 
      RSVP Sessions (Detailed) 
      =============================================================================== 
      ------------------------------------------------------------------------------- 
      LSP : LSP-P-6-PE-2::path-P-6-PE-2 
      ------------------------------------------------------------------------------- 
      From            : 192.0.2.6             To             : 192.0.2.2 
      Tunnel ID       : 1                     LSP ID         : 16896 
      Style           : SE                    State          : Up 
      Session Type    : Originate              
      In Interface    : n/a                   Out Interface  : 1/1/1 
      In IF Name      : n/a                    
      Out IF Name     : int-P-6-PE-2           
      In Label        : n/a                   Out Label      : 524287
      Previous Hop    : n/a                   Next Hop       : 192.168.26.1 
      Hops            :                        
                        192.168.26.1(S) 
      SetupPriority   : 7                     Hold Priority  : 0 
      Class Type      : 0                      
      SubGrpOrig ID   : 0                     SubGrpOrig Addr:  
      P2MP ID         : 0                      
      FrrAvailType    : N/A                    
      FrrSrlgStrict   : N/A                   SrlgDisjoint   : N/A 
      
      Path Recd       : 0                     Path Sent      : 59 
      Resv Recd       : 60                    Resv Sent      : 0 
      Summary msgs    :                        
      SPath Recd      : 0                     SPath Sent     : 0 
      SResv Recd      : 0                     SResv Sent     : 0 
      LSP Attr Flags  : N/A                    
      =============================================================================== 
      
    3. LDP label 524285 is added as the middle label on each user packet.

      *A:P-6# show router ldp bindings active prefixes prefix 192.0.2.2/32  
      
      =============================================================================== 
      LDP Bindings (IPv4 LSR ID 192.0.2.6) 
                   (IPv6 LSR ID ::) 
      =============================================================================== 
      Label Status: 
              U - Label In Use, N - Label Not In Use, W - Label Withdrawn 
              WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route 
              e - Label ELC 
      FEC Flags: 
              LF - Lower FEC, UF - Upper FEC, M - Community Mismatch, 
              BA - ASBR Backup FEC 
              (S) - Static           (M) - Multi-homed Secondary Support 
              (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route 
              (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop 
              (C) - FEC resolved with class-based-forwarding 
      =============================================================================== 
      LDP IPv4 Prefix Bindings (Active) 
      =============================================================================== 
      Prefix                                      Op 
      IngLbl                                      EgrLbl 
      EgrNextHop                                  EgrIf/LspId 
      ------------------------------------------------------------------------------- 
      192.0.2.2/32                                Push 
        --                                        524285 
      192.0.2.2                                   LspId 1 
      
      192.0.2.2/32                                Swap 
      524270                                      524285
      192.0.2.2                                   LspId 1 
      
      ------------------------------------------------------------------------------- 
      No. of IPv4 Prefix Active Bindings: 2 
      =============================================================================== 
      

      Service label 524277 is added as the inner MP-BGP label on each user packet.

  6. Intra-area FEC resolving (ingress LER is PE-1, egress LER is PE-4).

    1. Verification endpoint node and associated RSVP tunnel.

      The first thing to do in the intra-area FEC resolving process is for PE-1 to perform an SPF calculation toward PE-4 to search for an eligible endpoint, as close as possible to PE-4. An endpoint is eligible when:

      • a T-LDP session exists between PE-1 and the endpoint node

      • tunneling is configured on the endpoint node

      • PE-1 received a label for the destination FEC from the endpoint

      • and an RSVP LSP that can be used for LDP over RSVP exists between PE-1 and the endpoint node

      First endpoint node in OSPF area 1 can be either P-5 or P-8 (only those nodes have a T-LDP session toward PE-1). With show router ldp bindings active prefixes prefix 192.0.2.4/32, it can be concluded that P-5 is the endpoint node. Furthermore, LSP ID 1 indicates that an RSVP LSP is used.

      *A:PE-1# show router ldp bindings active prefixes prefix 192.0.2.4/32  
      
      =============================================================================== 
      LDP Bindings (IPv4 LSR ID 192.0.2.1) 
                   (IPv6 LSR ID ::) 
      =============================================================================== 
      Label Status: 
              U - Label In Use, N - Label Not In Use, W - Label Withdrawn 
              WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route 
              e - Label ELC 
      FEC Flags: 
              LF - Lower FEC, UF - Upper FEC, M - Community Mismatch, 
              BA - ASBR Backup FEC 
              (S) - Static           (M) - Multi-homed Secondary Support 
              (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route 
              (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop 
              (C) - FEC resolved with class-based-forwarding 
      =============================================================================== 
      LDP IPv4 Prefix Bindings (Active) 
      =============================================================================== 
      Prefix                                      Op 
      IngLbl                                      EgrLbl 
      EgrNextHop                                  EgrIf/LspId 
      ------------------------------------------------------------------------------- 
      192.0.2.4/32                                Push 
        --                                        524269 
      192.0.2.5                                   LspId 1
      
      192.0.2.4/32                                Swap 
      524283                                      524269 
      192.0.2.5                                   LspId 1 
      
      ------------------------------------------------------------------------------- 
      No. of IPv4 Prefix Active Bindings: 2 
      =============================================================================== 
      
      *A:PE-1# show router mpls lsp 
      
      =============================================================================== 
      MPLS LSPs (Originating) 
      =============================================================================== 
      LSP Name                                            Tun     Fastfail  Adm  Opr 
        To                                                Id      Config          
      ------------------------------------------------------------------------------- 
      LSP-PE-1-P-5                                        1       No        Up   Up
        192.0.2.5
      LSP-PE-1-P-8                                        2       No        Up   Up 
        192.0.2.8                                                                 
      ------------------------------------------------------------------------------- 
      LSPs : 2 
      =============================================================================== 
      
      *A:PE-1# show router tunnel-table
      
      =============================================================================== 
      IPv4 Tunnel Table (Router: Base) 
      =============================================================================== 
      Destination           Owner     Encap TunnelId  Pref   Nexthop        Metric 
         Color                                                               
      ------------------------------------------------------------------------------- 
      192.0.2.2/32          ldp       MPLS  65540     9      192.0.2.5      30 
      192.0.2.3/32          ldp       MPLS  65541     9      192.0.2.5      40 
      192.0.2.4/32          ldp       MPLS  65538     9      192.0.2.5      30 
      192.0.2.5/32          rsvp      MPLS  1         7      192.168.15.2   16777215
      192.0.2.5/32          ldp       MPLS  65537     9      192.0.2.5      10 
      192.0.2.6/32          ldp       MPLS  65539     9      192.0.2.5      20 
      192.0.2.7/32          ldp       MPLS  65542     9      192.0.2.5      30 
      192.0.2.8/32          rsvp      MPLS  2         7      192.168.15.2   16777215 
      192.0.2.8/32          ldp       MPLS  65543     9      192.0.2.8      20 
      ------------------------------------------------------------------------------- 
      Flags: B = BGP or MPLS backup hop available 
             L = Loop-Free Alternate (LFA) hop available 
             E = Inactive best-external BGP route 
             k = RIB-API or Forwarding Policy backup hop 
      =============================================================================== 
      

      On node P-5, the same commands can be repeated for the final destination node (PE-4). Also there, an RSVP LSP toward PE-4 is used as transport tunnel for user packets.

      *A:P-5# show router ldp bindings active prefixes prefix 192.0.2.4/32  
      
      =============================================================================== 
      LDP Bindings (IPv4 LSR ID 192.0.2.5) 
                   (IPv6 LSR ID ::) 
      =============================================================================== 
      Label Status: 
              U - Label In Use, N - Label Not In Use, W - Label Withdrawn 
              WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route 
              e - Label ELC 
      FEC Flags: 
              LF - Lower FEC, UF - Upper FEC, M - Community Mismatch, 
              BA - ASBR Backup FEC 
              (S) - Static           (M) - Multi-homed Secondary Support 
              (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route 
              (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop 
              (C) - FEC resolved with class-based-forwarding 
      =============================================================================== 
      LDP IPv4 Prefix Bindings (Active) 
      =============================================================================== 
      Prefix                                      Op 
      IngLbl                                      EgrLbl 
      EgrNextHop                                  EgrIf/LspId 
      ------------------------------------------------------------------------------- 
      192.0.2.4/32                                Push 
        --                                        524285 
      192.0.2.4                                   LspId 2 
      
      192.0.2.4/32                                Swap 
      524269                                      524285 
      192.0.2.4                                   LspId 2
      
      ------------------------------------------------------------------------------- 
      No. of IPv4 Prefix Active Bindings: 2 
      =============================================================================== 
      
      *A:P-5# show router mpls lsp  
      
      =============================================================================== 
      MPLS LSPs (Originating) 
      =============================================================================== 
      LSP Name                                            Tun     Fastfail  Adm  Opr 
        To                                                Id      Config          
      ------------------------------------------------------------------------------- 
      LSP-P-5-PE-1                                        1       No        Up   Up 
        192.0.2.1                                                                 
      LSP-P-5-PE-4                                        2       No        Up   Up
        192.0.2.4
      LSP-P-5-P-6                                         3       Yes       Up   Up 
        192.0.2.6                                                                 
      LSP-P-5-P-7                                         4       Yes       Up   Up 
        192.0.2.7                                                                 
      LSP-P-5-P-8                                         5       Yes       Up   Up 
        192.0.2.8                                                                 
      ------------------------------------------------------------------------------- 
      LSPs : 5 
      =============================================================================== 
      
      *A:P-5# show router tunnel-table 
      
      =============================================================================== 
      IPv4 Tunnel Table (Router: Base) 
      =============================================================================== 
      Destination           Owner     Encap TunnelId  Pref   Nexthop        Metric 
         Color                                                               
      ------------------------------------------------------------------------------- 
      192.0.2.1/32          rsvp      MPLS  1         7      192.168.15.1   16777215 
      192.0.2.1/32          ldp       MPLS  65537     9      192.0.2.1      10 
      192.0.2.2/32          ldp       MPLS  65540     9      192.0.2.6      20 
      192.0.2.3/32          ldp       MPLS  65541     9      192.0.2.7      30 
      192.0.2.4/32          rsvp      MPLS  2         7      192.168.58.2   16777215
      192.0.2.4/32          ldp       MPLS  65538     9      192.0.2.4      20 
      192.0.2.6/32 [B]      rsvp      MPLS  3         7      192.168.56.2   10 
      192.0.2.6/32          ldp       MPLS  65539     9      192.0.2.6      10 
      192.0.2.7/32 [B]      rsvp      MPLS  4         7      192.168.56.2   20 
      192.0.2.7/32          ldp       MPLS  65542     9      192.0.2.7      20 
      192.0.2.8/32 [B]      rsvp      MPLS  5         7      192.168.58.2   10 
      192.0.2.8/32          ldp       MPLS  65543     9      192.0.2.8      10 
      ------------------------------------------------------------------------------- 
      Flags: B = BGP or MPLS backup hop available 
             L = Loop-Free Alternate (LFA) hop available 
             E = Inactive best-external BGP route 
             k = RIB-API or Forwarding Policy backup hop 
      ===============================================================================
      

      P-5 node acts as a stitching node to stitch RSVP LSPs. P-5 stitches LSP-PE-1-P-5 and LSP-P-5-PE-4 together.

      When the endpoint node (P-5) is defined, the corresponding RSVP LSP to this endpoint is chosen. Selection criteria are as follows (when ECMP=1). When RSVP LSPs are configured under the T-LDP tunneling command (maximum 4), the one with the lowest LSP metric is selected. When no RSVP LSPs are configured under the T-LDP tunneling command, LDP checks the tunnel table for all available RSVP LSPs. The RSVP LSP with the lowest metric and operational state up is selected.

    2. Traffic verification using a VPRN service (see VPRN 1 with LDP over RSVP and no intra-area PE connectivity ).

      If user traffic between PE-1 (ingress LER) and PE-4 (egress LER) is monitored, three labels are seen. The outer label is the transport label (distributed using RSVP protocol), the inner label is the service label (distributed using MP-BGP). LDP over RSVP adds an extra MPLS transport label between outer and inner label (distributed using LDP). This middle label is used to tell the endpoint node (P-5) what to do.

      The following command shows that transport label 524287 is added as the top RSVP label on each user packet sent from PE-1 to P-5.

      *A:PE-1# show router rsvp session lsp-name "LSP-PE-1-P-5::path-PE-1-P-5" detail  
      
      =============================================================================== 
      RSVP Sessions (Detailed) 
      =============================================================================== 
      ------------------------------------------------------------------------------- 
      LSP : LSP-PE-1-P-5::path-PE-1-P-5 
      ------------------------------------------------------------------------------- 
      From            : 192.0.2.1             To             : 192.0.2.5 
      Tunnel ID       : 1                     LSP ID         : 37888 
      Style           : SE                    State          : Up 
      Session Type    : Originate              
      In Interface    : n/a                   Out Interface  : 1/1/1 
      In IF Name      : n/a                    
      Out IF Name     : int-PE-1-P-5           
      In Label        : n/a                   Out Label      : 524287
      Previous Hop    : n/a                   Next Hop       : 192.168.15.2 
      Hops            :                        
                        192.168.15.2(S) 
      SetupPriority   : 7                     Hold Priority  : 0 
      Class Type      : 0                      
      SubGrpOrig ID   : 0                     SubGrpOrig Addr:  
      P2MP ID         : 0                      
      FrrAvailType    : N/A                    
      FrrSrlgStrict   : N/A                   SrlgDisjoint   : N/A 
      
      Path Recd       : 0                     Path Sent      : 61 
      Resv Recd       : 63                    Resv Sent      : 0 
      Summary msgs    :                        
      SPath Recd      : 0                     SPath Sent     : 0 
      SResv Recd      : 0                     SResv Sent     : 0 
      LSP Attr Flags  : N/A                    
      =============================================================================== 
      

      LDP over RSVP label 524269 is added as the middle LDP label on each user packet.

      *A:PE-1# show router ldp bindings active prefixes prefix 192.0.2.4/32 
      
      =============================================================================== 
      LDP Bindings (IPv4 LSR ID 192.0.2.1) 
                   (IPv6 LSR ID ::) 
      =============================================================================== 
      Label Status: 
              U - Label In Use, N - Label Not In Use, W - Label Withdrawn 
              WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route 
              e - Label ELC 
      FEC Flags: 
              LF - Lower FEC, UF - Upper FEC, M - Community Mismatch, 
              BA - ASBR Backup FEC 
              (S) - Static           (M) - Multi-homed Secondary Support 
              (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route 
              (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop 
              (C) - FEC resolved with class-based-forwarding 
      =============================================================================== 
      LDP IPv4 Prefix Bindings (Active) 
      =============================================================================== 
      Prefix                                      Op 
      IngLbl                                      EgrLbl 
      EgrNextHop                                  EgrIf/LspId 
      ------------------------------------------------------------------------------- 
      192.0.2.4/32                                Push 
        --                                        524269
      192.0.2.5                                   LspId 1 
      
      192.0.2.4/32                                Swap 
      524283                                      524269 
      192.0.2.5                                   LspId 1 
      
      ------------------------------------------------------------------------------- 
      No. of IPv4 Prefix Active Bindings: 2 
      =============================================================================== 
      

      Service label 524277 is added as the inner MP-BGP label on each user packet.

      Note:

      This label will not change at endpoint node (P-5). Ingress LER (PE-1) will push the service label to the user packet while the egress LER (PE-4) will pop the service label.

      *A:PE-1# show router bgp neighbor 192.0.2.5 received-routes vpn-ipv4 
      
      =============================================================================== 
       BGP Router ID:192.0.2.1        AS:64496       Local AS:64496       
      =============================================================================== 
       Legend - 
       Status codes  : u - used, s - suppressed, h - history, d - decayed, * - valid 
                       l - leaked, x - stale, > - best, b - backup, p - purge 
       Origin codes  : i - IGP, e - EGP, ? - incomplete 
      
      =============================================================================== 
      BGP VPN-IPv4 Routes 
      =============================================================================== 
      Flag  Network                                            LocalPref   MED 
            Nexthop (Router)                                   Path-Id     IGP Cost 
            As-Path                                                        Label 
      ------------------------------------------------------------------------------- 
      i     64496:1:10.0.1.0/24                                100         None 
            192.0.2.1                                          None        0 
            No As-Path                                                     524277 
      u*>i  64496:1:10.0.2.0/24                                100         None 
            192.0.2.2                                          None        30 
            No As-Path                                                     524277 
      u*>i  64496:1:10.0.4.0/24                                100         None 
            192.0.2.4                                          None        30 
            No As-Path                                                     524277 
      i     64496:1:172.16.1.0/30                              100         None 
            192.0.2.1                                          None        0 
            No As-Path                                                     524277 
      u*>i  64496:1:172.16.2.0/30                              100         None 
            192.0.2.2                                          None        30 
            No As-Path                                                     524277 
      u*>i  64496:1:172.16.4.0/30                              100         None 
            192.0.2.4                                          None        30 
            No As-Path                                                     524277 
      ------------------------------------------------------------------------------- 
      Routes : 6 
      ===============================================================================
      

      The following command shows that P-5 pushes RSVP transport label 524284 as the top label on each user packet sent on path-P-5-P-8-PE-4. This RSVP transport label is swapped by P-8 to label 524287.

      *A:P-5# show router mpls lsp "LSP-P-5-PE-4" path detail 
      
      =============================================================================== 
      MPLS LSP LSP-P-5-PE-4 Path  (Detail) 
      =============================================================================== 
      Legend :  
          @ - Detour Available              # - Detour In Use 
          b - Bandwidth Protected           n - Node Protected 
          s - Soft Preemption            
          S - Strict                        L - Loose 
          A - ABR                           + - Inherited 
      =============================================================================== 
      ------------------------------------------------------------------------------- 
      LSP LSP-P-5-PE-4 
      Path path-P-5-P-8-PE-4 
      ------------------------------------------------------------------------------- 
      LSP Name    : LSP-P-5-PE-4 
      From             : 192.0.2.5                
      To               : 192.0.2.4                
      Admin State      : Up                      Oper State        : Up 
      Path Name   : path-P-5-P-8-PE-4 
      Path LSP ID      : 56832                   Path Type         : Primary 
      Path Admin       : Up                      Path Oper         : Up 
      Out Interface    : 1/1/3                   Out Label         : 524284
      Path Up Time     : 0d 00:30:33             Path Down Time    : 0d 00:00:00 
      Retry Limit      : 0                       Retry Timer       : 30 sec 
      Retry Attempt    : 0                       Next Retry In     : 0 sec 
      
      BFD Configuration and State 
      Template         : None                    Ping Interval     : 60 
      Enable           : False                   State             : notApplicable 
      WaitForUpTimer   : 4 sec                   OperWaitForUpTimer: N/A 
      WaitForUpTmLeft  : 0 sec                    
      
      Adspec           : Disabled                Oper Adspec       : Disabled 
      PathCompMethod   : none                    OperPathCompMethod: none 
      MetricType       : igp                     Oper MetricType   : igp 
      Least Fill       : Disabled                Oper LeastFill    : Disabled 
      FRR              : Disabled                Oper FRR          : Disabled 
      Propagate Adm Grp: Disabled                Oper Prop Adm Grp : Disabled 
      Inter-area       : False                    
      
      PCE Report       : Disabled+               Oper PCE Report   : Disabled 
      PCE Control      : Disabled                Oper PCE Control  : Disabled 
      PCE Update ID    : 0                        
      
      Neg MTU          : 1564                    Oper MTU          : 1564 
      Bandwidth        : No Reservation          Oper Bandwidth    : 0 Mbps 
      Hop Limit        : 255                     Oper HopLimit     : 255 
      Record Route     : Record                  Oper Record Route : Record 
      Record Label     : Record                  Oper Record Label : Record 
      Setup Priority   : 7                       Oper SetupPriority: 7 
      Hold Priority    : 0                       Oper HoldPriority : 0
      
      Class Type       : 0                       Oper CT           : 0 
      Backup CT        : None                     
      MainCT Retry     : n/a                      
          Rem          :                          
      MainCT Retry     : 0                        
          Limit        :                          
      Include Groups   :                         Oper IncludeGroups:  
      None                                           None 
      Exclude Groups   :                         Oper ExcludeGroups:  
      None                                           None 
      
      Adaptive         : Enabled                 Oper Metric       : 16777215 
      Preference       : n/a                      
      Path Trans       : 1                       CSPF Queries      : 0 
      Failure Code     : noError 
      Failure Node : n/a 
      Explicit Hops    :                          
                        192.168.58.2(S) 
                     -> 192.168.48.1(S) 
      Actual Hops      :                          
          192.168.58.1(192.0.2.5)                      Record Label        : N/A 
       -> 192.168.58.2(192.0.2.8)                      Record Label        : 524284 
       -> 192.168.48.1                                 Record Label        : 524287 
      Resignal Eligible: False                    
      Last Resignal    : n/a                     CSPF Metric       : 0 
      ===============================================================================
      
      Note:

      show router rsvp session lsp-name LSP-P-5-PE-4::path-P-5-P-8-PE-4 detail cannot be used because it only shows the outgoing RSVP label toward node P-8. On node P-8, RSVP transport label 524284 will be swapped into RSVP transport label 524287 for the link from P-8 to PE-4.

      LDP label 524285 is added as the middle label on each user packet.

      *A:P-5# show router ldp bindings active prefixes prefix 192.0.2.4/32 
      
      =============================================================================== 
      LDP Bindings (IPv4 LSR ID 192.0.2.5) 
                   (IPv6 LSR ID ::) 
      =============================================================================== 
      Label Status: 
              U - Label In Use, N - Label Not In Use, W - Label Withdrawn 
              WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route 
              e - Label ELC 
      FEC Flags: 
              LF - Lower FEC, UF - Upper FEC, M - Community Mismatch, 
              BA - ASBR Backup FEC 
              (S) - Static           (M) - Multi-homed Secondary Support 
              (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route 
              (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop 
              (C) - FEC resolved with class-based-forwarding 
      =============================================================================== 
      LDP IPv4 Prefix Bindings (Active) 
      =============================================================================== 
      Prefix                                      Op 
      IngLbl                                      EgrLbl 
      EgrNextHop                                  EgrIf/LspId 
      ------------------------------------------------------------------------------- 
      192.0.2.4/32                                Push 
        --                                        524285 
      192.0.2.4                                   LspId 2 
      
      192.0.2.4/32                                Swap 
      524269                                      524285 
      192.0.2.4                                   LspId 2 
      
      ------------------------------------------------------------------------------- 
      No. of IPv4 Prefix Active Bindings: 2 
      =============================================================================== 
      

      Service label 524277 is added as the inner MP-BGP label on each user packet.

      *A:P-5# show router bgp neighbor 192.0.2.4 received-routes vpn-ipv4  
      =============================================================================== 
       BGP Router ID:192.0.2.5        AS:64496       Local AS:64496       
      =============================================================================== 
       Legend - 
       Status codes  : u - used, s - suppressed, h - history, d - decayed, * - valid 
                       l - leaked, x - stale, > - best, b - backup, p - purge 
       Origin codes  : i - IGP, e - EGP, ? - incomplete 
      
      =============================================================================== 
      BGP VPN-IPv4 Routes 
      =============================================================================== 
      Flag  Network                                            LocalPref   MED 
            Nexthop (Router)                                   Path-Id     IGP Cost 
            As-Path                                                        Label 
      ------------------------------------------------------------------------------- 
      *>i   64496:1:10.0.4.0/24                                100         None 
            192.0.2.4                                          None        20 
            No As-Path                                                     524277 
      *>i   64496:1:172.16.4.0/30                              100         None 
            192.0.2.4                                          None        20 
            No As-Path                                                     524277 
      ------------------------------------------------------------------------------- 
      Routes : 2 
      =============================================================================== 
      

Additional topics

prefer-tunnel-in-tunnel

If the next-hop router advertised the same FEC over link-level LDP (iLDP), LDP prefers the iLDP tunnel by default unless the user explicitly changed the default preference using the prefer-tunnel-in-tunnel command. When prefer-tunnel-in-tunnel is set, an LDP over RSVP tunnel has precedence.

Until now, no RSVP LSPs are configured inside the ldp targeted-session peer tunneling context. Therefore, two additional strict non-CSPF RSVP LSPs are added between ingress LER PE-1 and egress LER P-5. Both LSPs have an explicit metric setting and are applied inside the ldp tunneling context. On the Layer 3 interface between PE-1 and P-5, iLDP is enabled.

# on PE-1:
configure
    router Base
        ldp 
            interface-parameters
                interface "int-PE-1-P-5" dual-stack
                    ipv4
                        no shutdown
                    exit
                    no shutdown
                exit
            exit
# on P-5:
configure 
    router Base
        ldp 
            interface-parameters
                interface "int-P-5-PE-1" dual-stack
                    ipv4
                        no shutdown
                    exit
                    no shutdown
                exit
            exit
# on PE-1:
configure
    router Base
        mpls
            lsp "LSP-PE-1-P-5-metric100"
                to 192.0.2.5
                metric 100
                primary "path-PE-1-P-5"
                exit
                no shutdown
            exit
            lsp "LSP-PE-1-P-5-metric200"
                to 192.0.2.5
                metric 200
                primary "path-PE-1-P-5"
                exit
                no shutdown
            exit
# on PE-1:
configure 
    router Base
        ldp 
            targeted-session
                peer 192.0.2.5
                    tunneling
                        lsp "LSP-PE-1-P-5-metric100"
                        lsp "LSP-PE-1-P-5-metric200"
                    exit
                exit
            exit

The following tunnel table on node PE-1 contains four tunnels toward P-5: one LDP tunnel and three RSVP tunnels:

*A:PE-1# show router tunnel-table  

=============================================================================== 
IPv4 Tunnel Table (Router: Base) 
=============================================================================== 
Destination           Owner     Encap TunnelId  Pref   Nexthop        Metric 
   Color                                                               
------------------------------------------------------------------------------- 
192.0.2.2/32          ldp       MPLS  65540     9      192.168.15.2   30 
192.0.2.3/32          ldp       MPLS  65541     9      192.168.15.2   40 
192.0.2.4/32          ldp       MPLS  65538     9      192.168.15.2   30 
192.0.2.5/32          rsvp      MPLS  3         7      192.168.15.2   100
192.0.2.5/32          rsvp      MPLS  4         7      192.168.15.2   200
192.0.2.5/32          rsvp      MPLS  1         7      192.168.15.2   16777215
192.0.2.5/32          ldp       MPLS  65537     9      192.168.15.2   10
192.0.2.6/32          ldp       MPLS  65539     9      192.168.15.2   20 
192.0.2.7/32          ldp       MPLS  65542     9      192.168.15.2   30 
192.0.2.8/32          rsvp      MPLS  2         7      192.168.15.2   16777215 
192.0.2.8/32          ldp       MPLS  65543     9      192.168.15.2   20 
------------------------------------------------------------------------------- 
Flags: B = BGP or MPLS backup hop available 
       L = Loop-Free Alternate (LFA) hop available 
       E = Inactive best-external BGP route 
       k = RIB-API or Forwarding Policy backup hop 
=============================================================================== 

Tunnel ID 1 is a reference to LSP-PE-1-P-5. Tunnel ID 3 is a reference to LSP-PE-1-P-5-metric100. Tunnel ID 4 is a reference to LSP-PE-1-P-5-metric200 and owner LDP is a reference to iLDP.

Taken into account the FEC resolution rules, iLDP prevails, so no LDP over RSVP tunnel is used. The following command shows that the egress interface is 1/1/1; no RSVP LSP is used, so no LSP ID is present:

*A:PE-1# show router ldp bindings active prefixes prefix 192.0.2.5/32  

=============================================================================== 
LDP Bindings (IPv4 LSR ID 192.0.2.1) 
             (IPv6 LSR ID ::) 
=============================================================================== 
Label Status: 
        U - Label In Use, N - Label Not In Use, W - Label Withdrawn 
        WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route 
        e - Label ELC 
FEC Flags: 
        LF - Lower FEC, UF - Upper FEC, M - Community Mismatch, 
        BA - ASBR Backup FEC 
        (S) - Static           (M) - Multi-homed Secondary Support 
        (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route 
        (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop 
        (C) - FEC resolved with class-based-forwarding 
=============================================================================== 
LDP IPv4 Prefix Bindings (Active) 
=============================================================================== 
Prefix                                      Op 
IngLbl                                      EgrLbl 
EgrNextHop                                  EgrIf/LspId 
------------------------------------------------------------------------------- 
192.0.2.5/32                                Push 
  --                                        524271 
192.168.15.2                                1/1/1

192.0.2.5/32                                Swap 
524284                                      524271 
192.168.15.2                                1/1/1

------------------------------------------------------------------------------- 
No. of IPv4 Prefix Active Bindings: 2 
=============================================================================== 

This behavior can be changed by setting the prefer-tunnel-in-tunnel command in the ldp context. Now, the LDP over RSVP tunnel with the best (= lowest) metric is taken.

# on PE-1:
configure 
    router Base
        ldp
            prefer-tunnel-in-tunnel 

The following command shows that LSP ID 3 is used:

A:PE-1# show router ldp bindings active prefixes prefix 192.0.2.5/32 

=============================================================================== 
LDP Bindings (IPv4 LSR ID 192.0.2.1) 
             (IPv6 LSR ID ::) 
=============================================================================== 
Label Status: 
        U - Label In Use, N - Label Not In Use, W - Label Withdrawn 
        WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route 
        e - Label ELC 
FEC Flags: 
        LF - Lower FEC, UF - Upper FEC, M - Community Mismatch, 
        BA - ASBR Backup FEC 
        (S) - Static           (M) - Multi-homed Secondary Support 
        (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route 
        (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop 
        (C) - FEC resolved with class-based-forwarding 
=============================================================================== 
LDP IPv4 Prefix Bindings (Active) 
=============================================================================== 
Prefix                                      Op 
IngLbl                                      EgrLbl 
EgrNextHop                                  EgrIf/LspId 
------------------------------------------------------------------------------- 
192.0.2.5/32                                Push 
  --                                        524271 
192.0.2.5                                   LspId 3

192.0.2.5/32                                Swap 
524284                                      524271 
192.0.2.5                                   LspId 3

------------------------------------------------------------------------------- 
No. of IPv4 Prefix Active Bindings: 2 
===============================================================================

The following command shows that LSP ID 3 corresponds to LSP-PE-1-P-5-metric100:

*A:PE-1# show router mpls lsp  

=============================================================================== 
MPLS LSPs (Originating) 
=============================================================================== 
LSP Name                                            Tun     Fastfail  Adm  Opr 
  To                                                Id      Config          
------------------------------------------------------------------------------- 
LSP-PE-1-P-5                                        1       No        Up   Up 
  192.0.2.5                                                                 
LSP-PE-1-P-8                                        2       No        Up   Up 
  192.0.2.8                                                                 
LSP-PE-1-P-5-metric100                              3       No        Up   Up
  192.0.2.5
LSP-PE-1-P-5-metric200                              4       No        Up   Up 
  192.0.2.5                                                                 
------------------------------------------------------------------------------- 
LSPs : 4 
=============================================================================== 

When the LSP-PE-1-P-5-metric100 is disabled (shutdown), then the LSP-PE-1-P-5-metric200 becomes active.

# on PE-1:
configure
    router Base
        mpls 
            lsp "LSP-PE-1-P-5-metric100"
                shutdown

The following command shows that LSP ID 4 is used for traffic toward 192.0.2.5:

*A:PE-1# show router ldp bindings active prefixes prefix 192.0.2.5/32  

=============================================================================== 
LDP Bindings (IPv4 LSR ID 192.0.2.1) 
             (IPv6 LSR ID ::) 
=============================================================================== 
Label Status: 
        U - Label In Use, N - Label Not In Use, W - Label Withdrawn 
        WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route 
        e - Label ELC 
FEC Flags: 
        LF - Lower FEC, UF - Upper FEC, M - Community Mismatch, 
        BA - ASBR Backup FEC 
        (S) - Static           (M) - Multi-homed Secondary Support 
        (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route 
        (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop 
        (C) - FEC resolved with class-based-forwarding 
=============================================================================== 
LDP IPv4 Prefix Bindings (Active) 
=============================================================================== 
Prefix                                      Op 
IngLbl                                      EgrLbl 
EgrNextHop                                  EgrIf/LspId 
------------------------------------------------------------------------------- 
192.0.2.5/32                                Push 
  --                                        524271 
192.0.2.5                                   LspId 4

192.0.2.5/32                                Swap 
524284                                      524271 
192.0.2.5                                   LspId 4

------------------------------------------------------------------------------- 
No. of IPv4 Prefix Active Bindings: 2 
=============================================================================== 

The following command shows that LSP ID 4 corresponds to LSP-PE-1-P-5-metric200:

*A:PE-1# show router mpls lsp 

=============================================================================== 
MPLS LSPs (Originating) 
=============================================================================== 
LSP Name                                            Tun     Fastfail  Adm  Opr 
  To                                                Id      Config          
------------------------------------------------------------------------------- 
LSP-PE-1-P-5                                        1       No        Up   Up 
  192.0.2.5                                                                 
LSP-PE-1-P-8                                        2       No        Up   Up 
  192.0.2.8                                                                 
LSP-PE-1-P-5-metric100                              3       No        Dwn  Dwn 
  192.0.2.5                                                                 
LSP-PE-1-P-5-metric200                              4       No        Up   Up
  192.0.2.5
------------------------------------------------------------------------------- 
LSPs : 4 
=============================================================================== 

When LSP-PE-1-P-5-metric200 is disabled (shutdown), iLDP resumes.

# on PE-1:
configure 
    router Base
        mpls 
            lsp "LSP-PE-1-P-5-metric200" 
                shutdown

The following command shows that iLDP is used and the egress interface is port 1/1/1:

*A:PE-1# show router ldp bindings active prefixes prefix 192.0.2.5/32 

=============================================================================== 
LDP Bindings (IPv4 LSR ID 192.0.2.1) 
             (IPv6 LSR ID ::) 
=============================================================================== 
Label Status: 
        U - Label In Use, N - Label Not In Use, W - Label Withdrawn 
        WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route 
        e - Label ELC 
FEC Flags: 
        LF - Lower FEC, UF - Upper FEC, M - Community Mismatch, 
        BA - ASBR Backup FEC 
        (S) - Static           (M) - Multi-homed Secondary Support 
        (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route 
        (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop 
        (C) - FEC resolved with class-based-forwarding 
=============================================================================== 
LDP IPv4 Prefix Bindings (Active) 
=============================================================================== 
Prefix                                      Op 
IngLbl                                      EgrLbl 
EgrNextHop                                  EgrIf/LspId 
------------------------------------------------------------------------------- 
192.0.2.5/32                                Push 
  --                                        524271 
192.168.15.2                                1/1/1

192.0.2.5/32                                Swap 
524284                                      524271 
192.168.15.2                                1/1/1

------------------------------------------------------------------------------- 
No. of IPv4 Prefix Active Bindings: 2 
=============================================================================== 

Intra-PE connectivity changes LDP over RSVP behavior

VPRN 1 with LDP over RSVP and intra-area PE connectivity shows two metro areas; both of the intra PEs are physically connected with each other. Compared with the previous figures, PE-1 is directly connected to PE-4 and PE-2 is directly connected to PE-3 (up to the OSPF level).

Figure 3. VPRN 1 with LDP over RSVP and intra-area PE connectivity

The SPF path calculation on PE-1 toward destination (PE-4) does not point to node P-5 anymore (as was seen before), but now points directly to PE-4 (shortest, lowest IGP metric). As a conclusion, it can be said that when possible intra-area endpoint nodes are not part of the calculated SPF path, LDP over RSVP is not preferred anymore. For this situation, it is advisable to configure iLDP on the intra-PE interfaces to have a fallback mechanism.

This is configured on PE-1 and PE-4 as follows:

# on PE-1:
configure 
    router Base
        interface "int-PE-1-PE-4"
            address 192.168.14.1/30
            port 1/1/2
        exit
        ospf 0
            area 0.0.0.1
                interface "int-PE-1-PE-4"
                    interface-type point-to-point
                exit
            exit
        exit
# on PE-4:
configure 
    router Base
        interface "int-PE-4-PE-1"
            address 192.168.14.2/30
            port 1/1/1
        exit
        ospf 0
            area 0.0.0.1
                interface "int-PE-4-PE-1"
                    interface-type point-to-point
                exit
            exit
        exit

LDP is configured on the interfaces between PE-1 and PE-4, as follows:

# on PE-1:
configure
    router Base
        ldp 
            interface-parameters
                interface "int-PE-1-PE-4" dual-stack
                    ipv4
                        no shutdown
                    exit
                    no shutdown
                exit
            exit
# on PE-4:
configure
    router Base
        ldp
            interface-parameters
                interface "int-PE-4-PE-1" dual-stack
                    ipv4
                        no shutdown
                    exit
                    no shutdown 
                exit
            exit

From the moment iLDP is configured, an LDP LSP is set up. Intra-area PE traffic will flow over this LDP LSP.

*A:PE-1# show router tunnel-table 192.0.2.4/32  

=============================================================================== 
IPv4 Tunnel Table (Router: Base) 
=============================================================================== 
Destination           Owner     Encap TunnelId  Pref   Nexthop        Metric 
   Color                                                               
------------------------------------------------------------------------------- 
192.0.2.4/32          ldp       MPLS  65544     9      192.168.14.2   10 
------------------------------------------------------------------------------- 
Flags: B = BGP or MPLS backup hop available 
       L = Loop-Free Alternate (LFA) hop available 
       E = Inactive best-external BGP route 
       k = RIB-API or Forwarding Policy backup hop 
===============================================================================  

If user traffic is monitored between ingress LER PE-1 and egress LER PE-4, only two labels are seen. The outer label is the transport label distributed using LDP; the inner label is the service label distributed using MP-BGP. No LDP over RSVP label is present anymore. The following command shows that LDP transport label 524285 is pushed by PE-1 as the outer label on packets destined to PE-4:

*A:PE-1# show router ldp bindings active prefixes prefix 192.0.2.4/32  

=============================================================================== 
LDP Bindings (IPv4 LSR ID 192.0.2.1) 
             (IPv6 LSR ID ::) 
=============================================================================== 
Label Status: 
        U - Label In Use, N - Label Not In Use, W - Label Withdrawn 
        WP - Label Withdraw Pending, BU - Alternate For Fast Re-Route 
        e - Label ELC 
FEC Flags: 
        LF - Lower FEC, UF - Upper FEC, M - Community Mismatch, 
        BA - ASBR Backup FEC 
        (S) - Static           (M) - Multi-homed Secondary Support 
        (B) - BGP Next Hop     (BU) - Alternate Next-hop for Fast Re-Route 
        (I) - SR-ISIS Next Hop (O) - SR-OSPF Next Hop 
        (C) - FEC resolved with class-based-forwarding 
=============================================================================== 
LDP IPv4 Prefix Bindings (Active) 
=============================================================================== 
Prefix                                      Op 
IngLbl                                      EgrLbl 
EgrNextHop                                  EgrIf/LspId 
------------------------------------------------------------------------------- 
192.0.2.4/32                                Push 
  --                                        524285 
192.168.14.2                                1/1/2

192.0.2.4/32                                Swap 
524283                                      524285 
192.168.14.2                                1/1/2

------------------------------------------------------------------------------- 
No. of IPv4 Prefix Active Bindings: 2 
=============================================================================== 

Service label 524277 is added as the inner MP-BGP label on each user packet.

*A:PE-1# show router bgp neighbor 192.0.2.5 received-routes vpn-ipv4  
=============================================================================== 
 BGP Router ID:192.0.2.1        AS:64496       Local AS:64496       
=============================================================================== 
 Legend - 
 Status codes  : u - used, s - suppressed, h - history, d - decayed, * - valid 
                 l - leaked, x - stale, > - best, b - backup, p - purge 
 Origin codes  : i - IGP, e - EGP, ? - incomplete 

=============================================================================== 
BGP VPN-IPv4 Routes 
=============================================================================== 
Flag  Network                                            LocalPref   MED 
      Nexthop (Router)                                   Path-Id     IGP Cost 
      As-Path                                                        Label 
------------------------------------------------------------------------------- 
i     64496:1:10.0.1.0/24                                100         None 
      192.0.2.1                                          None        0 
      No As-Path                                                     524277 
u*>i  64496:1:10.0.2.0/24                                100         None 
      192.0.2.2                                          None        30 
      No As-Path                                                     524277 
u*>i  64496:1:10.0.4.0/24                                100         None 
      192.0.2.4                                          None        10 
      No As-Path                                                     524277 
i     64496:1:172.16.1.0/30                              100         None 
      192.0.2.1                                          None        0 
      No As-Path                                                     524277 
u*>i  64496:1:172.16.2.0/30                              100         None 
      192.0.2.2                                          None        30 
      No As-Path                                                     524277 
u*>i  64496:1:172.16.4.0/30                              100         None 
      192.0.2.4                                          None        10 
      No As-Path                                                     524277 
------------------------------------------------------------------------------- 
Routes : 6 
=============================================================================== 

Conclusion

LDP over RSVP allows tunneling of user packets toward an LDP far-end destination inside an RSVP LSP (with the benefits of RSVP LSPs, fast-reroute (FRR) and traffic engineering (TE)). The main application of this feature is for deployment of MPLS based services, for example, VPRN, virtual leased line (VLL), and virtual private LAN service (VPLS) services, in large networks where a full mesh of LSPs reaches the limits of scalability.