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.
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
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 exitBecause 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-rsvpTo 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 exitConfigure 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 exitThe 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 excludeCreate 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 =============================================================================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 exitAs 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.
Inter-area FEC resolving (ingress LER is PE-1, egress LER is PE-2)
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.
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 shutdownIn 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 shutdownIf 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 ===============================================================================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.
Intra-area FEC resolving (ingress LER is PE-1, egress LER is PE-4).
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.
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).
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.