P2MP mLDP Inter-AS Model C for EVPN-MPLS Services

This chapter provides information about P2MP mLDP Inter-AS Model C for EVPN-MPLS Services.

Topics in this chapter include:

Applicability

This chapter was initially written for SR OS Release 15.0.R5, but the CLI in the current edition is based on SR OS Release 21.5.R1.

Point-to-Multipoint Multicast Label Distribution Protocol (P2MP mLDP) for Broadcast, Unknown Unicast, and Multicast (BUM) traffic in EVPN-MPLS networks is supported in SR OS Release 14.0.R1, and later. EVPN with P2MP mLDP LSPs is supported in a seamless MPLS or inter-AS model C scenario in SR OS Release 15.0.R1, and later. This chapter describes the inter-AS model C scenario, but the configuration for seamless MPLS is similar.

Overview

Chapter P2MP mLDP Tunnels for BUM Traffic in EVPN-MPLS Services describes P2MP mLDP within an Autonomous System (AS). PEs configured as root-and-leaf can send BUM traffic over P2MP mLDP tunnels; PEs configured as not root-and-leaf (that is, leaf-only) can only send BUM traffic over Ingress Replication (IR) tunnels. Both types of PEs (root-and-leaf and leaf-only) can receive BUM traffic over either P2MP mLDP tunnels or IR tunnels.

When provider-tunnel inclusive mldp is enabled in an EVPN-MPLS service in combination with root-and-leaf and bgp-evpn>ingress-repl-inc-mcast-advertisement, the system will send an Inclusive Multicast Ethernet Tag (IMET) route with a composite tunnel type (IMET-P2MP-IR) in the provider tunnel attributed.

Inter-AS VPN model C is described in chapters Inter-AS VPRN Model C and Inter-AS Model C for VLL. Labeled IPv4 unicast BGP is used to provide inter-AS connectivity. The system IP addresses within each AS are exported by the Autonomous System Border Routers (ASBRs) and a multi-hop BGP session is established between root node and leaf node for address family EVPN. The root node advertises a composite IMET-P2MP-IR route to the leaf nodes and the leaf nodes advertise an IMET-IR route to the root node. Inter-AS Model C for P2MP mLDP shows an example topology with root node PE-1 in AS 64501 and leaf node PE-4 in AS 64502. P-2 and P-3 are ASBRs.

Figure 1. Inter-AS Model C for P2MP mLDP

The composite IMET-P2MP-IR route received by leaf node PE-4 contains the root node (192.0.2.1) and the LSP ID (0x2001) that will be used by the nodes to set up a P2MP mLDP tree toward the root.

# on PE-4:
3 2021/06/02 08:31:13.913 UTC MINOR: DEBUG #2001 Base Peer 1: 192.0.2.1
"Peer 1: 192.0.2.1: UPDATE
Peer 1: 192.0.2.1 - Received BGP UPDATE:
    Withdrawn Length = 0
    Total Path Attr Length = 92
    Flag: 0x90 Type: 14 Len: 28 Multiprotocol Reachable NLRI:
        Address Family EVPN
        NextHop len 4 NextHop 192.0.2.1
        Type: EVPN-INCL-MCAST Len: 17 RD: 192.0.2.1:1, tag: 0, orig_addr len: 32,
                              orig_addr: 192.0.2.1 
    Flag: 0x40 Type: 1 Len: 1 Origin: 0
    Flag: 0x40 Type: 2 Len: 6 AS Path:
        Type: 2 Len: 1 < 64501 >
    Flag: 0xc0 Type: 16 Len: 16 Extended Community:
        target:64501:1
        bgp-tunnel-encap:MPLS
    Flag: 0xc0 Type: 22 Len: 25 PMSI:
        Tunnel-type Composite LDP P2MP IR (130)
        Flags: (0x0)[Type: None BM: 0 U: 0 Leaf: not required]
        MPLS Label1 Ag  0
        MPLS Label2 IR 8388544
        Root-Node 192.0.2.1, LSP-ID 0x2001
"

The Provider Multicast Service Interface (PMSI) tunnel attribute for tunnel type 130 (composite tunnel) has two MPLS labels, of which MPLS label 1 always equals zero in SR OS Release 21.5.R1, because SR OS does not support aggregated P2MP tunnels. MPLS label 2 is used by the downstream nodes to set up the EVPN-MPLS destination to the root node and add it to the default multicast list. The actual MPLS label only uses the high-order 20 bits out of the 24 bits advertised in the MPLS label. Therefore, the value 8388544 needs to be divided by 16 to get the MPLS label value: 8388544/16 = 524284. This is due to the debug message being shown before the router can parse the label field and see whether it corresponds to an MPLS label (20 bits) or a VXLAN VNI (24 bits). The following command on PE-4 shows the EVPN-MPLS destination 192.0.2.1 with MPLS label 524284 using a BGP transport tunnel:

*A:PE-4# show service id 1 evpn-mpls
 
===============================================================================
BGP EVPN-MPLS Dest
===============================================================================
TEP Address     Egr Label     Num. MACs   Mcast           Last Change
                Transport:Tnl                             Sup BCast Domain
-------------------------------------------------------------------------------
192.0.2.1       524284        0           bum             06/02/2021 08:31:14
                bgp:262146                                No
-------------------------------------------------------------------------------
Number of entries : 1
-------------------------------------------------------------------------------
===============================================================================
---snip---

The use of mLDP with recursive opaque values is specified in RFC 6512.

When the leaf node PE-4 receives the composite IMET-P2MP-IR route from the root node PE-1, a P2MP mLDP tree needs to be established from the leaf node to the root node. Leaf node PE-4 resolves the IP address of PE-1 to a labeled BGP route with next-hop ASBR P-3. PE-4 then sends an mLDP FEC with root node ASBR P-3 and an opaque value containing the root PE-1 and an LSP ID that was advertised in the IMET-P2MP-IR route, as follows:

# on PE-4:
4 2021/06/02 08:31:13.915 UTC MINOR: DEBUG #2001 Base LDP
"LDP: LDP
Send Label Mapping packet (msgId 40) to 192.0.2.3:0
Protocol version = 1
Label 524283 advertised for the following FECs
P2MP: root = 192.0.2.3, T: 7, L: 17 (InnerRoot: 192.0.2.1 T: 1, L: 4, TunnelId: 8193)
"

T: 7 indicates the MLDP recursive FEC type 7. The tunnel ID 8193 corresponds to the hexadecimal value 0x2001 sent by the root node PE-1, which is the inner root 192.0.2.1 in the recursive opaque value.

When ASBR P-3 receives this mLDP FEC, it identifies itself as root node and resolves the recursive opaque value (PE-1, LSP ID) and creates a new mLDP FEC element with root node ASBR P-2 and an identical opaque value (PE-1, LSP ID). The following mLDP FEC is sent to ASBR P-2:

# on P-3:
12 2021/06/02 08:32:36.794 UTC MINOR: DEBUG #2001 Base LDP
"LDP: LDP
Send Label Mapping packet (msgId 34) to 192.168.23.1:0
Protocol version = 1
Label 524279 advertised for the following FECs
P2MP: root = 192.168.23.1, T: 7, L: 17 (InnerRoot: 192.0.2.1 T: 1, L: 4, TunnelId: 8193)
"

ASBR P-2 receives the mLDP FEC and finds that it is the root node. P-2 creates a new mLDP FEC, but no recursion is required because P-2 knows the IP address of PE-1 through the IGP. P-2 sends the following mLDP FEC with root node PE-1, LSP ID 8193, and mLDP FEC type 1.

# on P-2:
12 2021/06/02 08:32:36.814 UTC MINOR: DEBUG #2001 Base LDP
"LDP: LDP
Send Label Mapping packet (msgId 50) to 192.0.2.1:0
Protocol version = 1
Label 524279 advertised for the following FECs
P2MP: root = 192.0.2.1, T: 1, L: 4, TunnelId: 8193
"

Configuration

The example topology was already shown in Inter-AS Model C for P2MP mLDP. The initial configuration includes the following:

  • Cards, MDAs, ports

  • Router interfaces

  • OSPF as IGP within each AS (alternatively, IS-IS can be used)

  • LDP enabled within each AS

The following two scenarios are configured:

  • Inter-AS model C for mLDP

  • Optimized inter-AS model C for mLDP

Inter-AS Model C for mLDP

The initial BGP configuration on the PEs only includes a label-IPv4 peering with the ASBRs. The BGP configuration on PE-1 is as follows:

# on PE-1:
configure 
    router Base
        bgp
            group "iBGP"
                type internal
                neighbor 192.0.2.2
                    family label-ipv4
                exit

On the ASBRs, BGP is configured for address family label-IPv4, both internal to PE-1 and external to the peer ASBR. The BGP configuration on P-2 is as follows:

# on P-2:
configure
    router Base
        bgp
            group "eBGP"
                type external
                neighbor 192.168.23.2
                    family label-ipv4
                    export "PE-sys-to-labeled-BGP"
                    local-as 64501
                    peer-as 64502
                    split-horizon
                exit
            exit
            group "iBGP"
                type internal
                neighbor 192.0.2.1
                    family label-ipv4
                exit
            exit

The BGP configuration on ASBR P-3 is similar, but the IP addresses are different and the local AS and peer AS are swapped. The following export policy is identical on both ASBRs P-2 and P-3:

# on P-2, P-3:
configure
    router
        policy-options
            begin
            prefix-list "sysPE"
                prefix 192.0.2.0/24 longer
            exit
            policy-statement "PE-sys-to-labeled-BGP"
                entry 10
                    from
                        prefix-list "sysPE"
                    exit
                    to
                        protocol bgp-label
                    exit
                    action accept
                    exit
                exit
            exit
            commit

This policy exports the system prefixes as label-IPv4 routes to the eBGP peer.

When a P2MP mLDP tree must be established across ASs, LDP needs to be enabled on the interface between the ASBRs with local-lsr-id interface instead of the default value "system". The LDP configuration on P-2 is as follows:

# on P-2:
configure
    router
        ldp
            interface-parameters
                interface "int-P-2-P-3"
                    ipv4
                        local-lsr-id interface
                    exit
                exit

With this LDP configuration, a link adjacency will be established toward the interface IP address instead of the system address, as follows:

*A:P-2# show router ldp session ipv4
 
==============================================================================
LDP IPv4 Sessions
==============================================================================
Peer LDP Id         Adj Type  State         Msg Sent  Msg Recv  Up Time
------------------------------------------------------------------------------
192.0.2.1:0         Link      Established   229       229       0d 00:09:48
192.168.23.2:0      Link      Established   137       140       0d 00:05:46
------------------------------------------------------------------------------
No. of IPv4 Sessions: 2
==============================================================================

However, this LDP configuration is insufficient for the resolution of mLDP FEC as link LSR ID. LDP needs a /32 route instead of a /30 route, so the following /32 static route is configured on P-2:

# on P-2:
configure
    router
        static-route-entry 192.168.23.2/32
            next-hop 192.168.23.2
                no shutdown
            exit
        exit

The configuration on ASBR P-3 is similar for static route 192.168.23.1/32. When this static route is not configured, no mLDP label mapping message will be sent from P-3 to P-2, so the mLDP P2MP tree cannot be established.

On PE-1, VPLS 1 is configured with mLDP root-and-leaf, as follows:

# on PE-1:
configure
    service
        vpls 1 name "EVI-1" customer 1 create
            bgp
                route-target export target:64501:1 import target:64502:1
            exit
            bgp-evpn
                ingress-repl-inc-mcast-advertisement
                evi 1
                mpls bgp 1
                    ingress-replication-bum-label
                    auto-bind-tunnel
                        resolution any
                    exit
                    no shutdown
                exit
            exit
            provider-tunnel
                inclusive
                    owner bgp-evpn-mpls
                    root-and-leaf
                    mldp
                    no shutdown
                exit
            exit
            stp
                shutdown
            exit
            sap 1/2/1:1 create
                no shutdown
            exit
            no shutdown

On PE-4, VPLS 1 is configured with mLDP leaf-only (no root-and-leaf, which is default), as follows:

# on PE-4:
configure
    service
        vpls 1 name "EVI-1" customer 1 create
            bgp
                route-target export target:64502:1 import target:64501:1
            exit
            bgp-evpn
                evi 1
                mpls bgp 1
                    ingress-replication-bum-label
                    auto-bind-tunnel
                        resolution any
                    exit
                    no shutdown
                exit
            exit
            provider-tunnel
                inclusive
                    owner bgp-evpn-mpls
                    mldp
                    no shutdown
                exit
            exit
            stp
                shutdown
            exit
            sap 1/2/1:1 create
                no shutdown
            exit
            no shutdown

The Route Distinguisher (RD) is auto-derived from EVI 1, but the route target (RT) should not be auto-derived, because the export RT on PE-1 must match the import RT on PE-4, and vice versa. It is an option to configure an identical RT on all PEs, such as 1:1, but in this example, the export RT on PE-1 is 64501:1, which equals the import RT on PE-4. When the RTs do not match, the BGP routes will be received at the PE in the peer AS, but they will not become active and no mLDP P2MP tree can be established.

Multi-hop BGP peering is configured between PE-1 and PE-4 for address family EVPN. The external BGP configuration on PE-1 is as follows:

# on PE-1:
configure 
    router
        bgp
            split-horizon
            group eBGP
                family evpn
                multihop 10
                local-as 64501
                peer-as 64502
                neighbor 192.0.2.4
                exit
            exit

The external BGP configuration on PE-4 is similar, but the local AS and peer AS are swapped, and the neighbor IP address is different.

Inter-AS Model C for mLDP - Verification

The following BGP summary shows that P-2 has sent and received two prefixes with its eBGP peer P-3 and has advertised two prefixes to its iBGP peer PE-1:

*A:P-2# show router bgp summary all 
 
===============================================================================
BGP Summary
===============================================================================
Legend : D - Dynamic Neighbor
===============================================================================
Neighbor
Description
ServiceId          AS PktRcvd InQ  Up/Down   State|Rcv/Act/Sent (Addr Family)
                      PktSent OutQ
-------------------------------------------------------------------------------
192.0.2.1
Def. Instance  64501       11    0 00h04m03s 0/0/2 (Lbl-IPv4)
                           13    0           
192.168.23.2
Def. Instance  64502       12    0 00h03m54s 2/2/2 (Lbl-IPv4)
                           12    0           
 
-------------------------------------------------------------------------------

ASBR P-2 advertised the following prefixes from AS 64501 to its neighbor P-3:

*A:P-2# show router bgp neighbor 192.168.23.2 advertised-routes label-ipv4 
===============================================================================
 BGP Router ID:192.0.2.2        AS:64501       Local AS:64501      
===============================================================================
 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 Routes
===============================================================================
Flag  Network                                            LocalPref   MED
      Nexthop (Router)                                   Path-Id     IGP Cost
      As-Path                                                        Label
-------------------------------------------------------------------------------
i     192.0.2.1/32                                       n/a         10
      192.168.23.1                                       None        n/a
      64501                                                          524284
i     192.0.2.2/32                                       n/a         None
      192.168.23.1                                       None        n/a
      64501                                                          524285
-------------------------------------------------------------------------------
Routes : 2
===============================================================================

ASBR P-2 received the following prefixes from AS 64502 from its neighbor P-3. Both routes are used.

*A:P-2# show router bgp neighbor 192.168.23.2 received-routes label-ipv4 
===============================================================================
 BGP Router ID:192.0.2.2        AS:64501       Local AS:64501      
===============================================================================
 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 Routes
===============================================================================
Flag  Network                                            LocalPref   MED
      Nexthop (Router)                                   Path-Id     IGP Cost
      As-Path                                                        Label
-------------------------------------------------------------------------------
u*>i  192.0.2.3/32                                       n/a         None
      192.168.23.2                                       None        0
      64502                                                          524285
u*>i  192.0.2.4/32                                       n/a         10
      192.168.23.2                                       None        0
      64502                                                          524284
-------------------------------------------------------------------------------
Routes : 2
===============================================================================

These routes are advertised by P-2 to its iBGP neighbor PE-1, so PE-1 will have the same label-IPv4 routes. The following command shows the route table on PE-1 that includes tunneled routes to P-3 and PE-4 in AS 64502.

*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     00h06m21s  0
       system                                                       0
192.0.2.2/32                                  Remote  OSPF      00h06m13s  10
       192.168.12.2                                                 10
192.0.2.3/32                                  Remote  BGP_LABEL 00h03m20s  170
       192.0.2.2 (tunneled)                                         10
192.0.2.4/32                                  Remote  BGP_LABEL 00h03m20s  170
       192.0.2.2 (tunneled)                                         10
192.168.12.0/30                               Local   Local     00h06m21s  0
       int-PE-1-P-2                                                 0
-------------------------------------------------------------------------------
No. of Routes: 5
Flags: n = Number of times nexthop is repeated
       B = BGP backup route available
       L = LFA nexthop available
       S = Sticky ECMP requested
===============================================================================

The following command shows the tunnel table on PE-1:

*A:PE-1# show router tunnel-table 
 
===============================================================================
IPv4 Tunnel Table (Router: Base)
===============================================================================
Destination           Owner     Encap TunnelId  Pref   Nexthop        Metric
   Color                                                              
-------------------------------------------------------------------------------
127.0.128.0/32        sdp       MPLS  32767     5      127.0.128.0    0
192.0.2.2/32          ldp       MPLS  65537     9      192.168.12.2   10
192.0.2.3/32          bgp       MPLS  262145    12     192.0.2.2      1000
192.0.2.4/32          bgp       MPLS  262146    12     192.0.2.2      1000
-------------------------------------------------------------------------------
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
===============================================================================

The tunnels toward P-3 and PE-4 are BGP tunnels. The SDP in the list is auto-created on the root node by mLDP. The output of these show commands on PE-4 is similar, but no SDP will be created on a leaf-only node.

The route-table on ASBR P-2 includes tunneled routes toward P-3 and PE-4 and a static route to 192.168.23.2/32, as follows:

*A:P-2# 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                                  Remote  OSPF      00h06m24s  10
       192.168.12.1                                                 10
192.0.2.2/32                                  Local   Local     00h06m25s  0
       system                                                       0
192.0.2.3/32                                  Remote  BGP_LABEL 00h03m50s  170
       192.168.23.2                                                 0
192.0.2.4/32                                  Remote  BGP_LABEL 00h03m50s  170
       192.168.23.2                                                 0
192.168.12.0/30                               Local   Local     00h06m25s  0
       int-P-2-PE-1                                                 0
192.168.23.0/30                               Local   Local     00h06m25s  0
       int-P-2-P-3                                                  0
192.168.23.2/32                               Remote  Static    00h00m28s  5
       192.168.23.2                                                 1
-------------------------------------------------------------------------------
No. of Routes: 7
Flags: n = Number of times nexthop is repeated
       B = BGP backup route available
       L = LFA nexthop available
       S = Sticky ECMP requested
===============================================================================

The tunnel table on P-2 has an LDP tunnel toward PE-1 and a BGP tunnel toward P-3 and PE-4, as follows:

*A:P-2# show router tunnel-table 
 
===============================================================================
IPv4 Tunnel Table (Router: Base)
===============================================================================
Destination           Owner     Encap TunnelId  Pref   Nexthop        Metric
   Color                                                              
-------------------------------------------------------------------------------
192.0.2.1/32          ldp       MPLS  65537     9      192.168.12.1   10
192.0.2.3/32          bgp       MPLS  262146    12     192.168.23.2   1000
192.0.2.4/32          bgp       MPLS  262145    12     192.168.23.2   1000
-------------------------------------------------------------------------------
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
===============================================================================

One BGP-EVPN IMET route is received and used on PE-1:

*A:PE-1# show router bgp routes evpn incl-mcast 
===============================================================================
 BGP Router ID:192.0.2.1        AS:64501       Local AS:64501      
===============================================================================
 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 EVPN Inclusive-Mcast Routes
===============================================================================
Flag  Route Dist.         OrigAddr
      Tag                 NextHop
-------------------------------------------------------------------------------
u*>i  192.0.2.4:1         192.0.2.4
      0                   192.0.2.4
 
-------------------------------------------------------------------------------
Routes : 1
===============================================================================

The preceding route is an IMET-IR route received from node PE-4, as follows:

*A:PE-1# show router bgp routes evpn incl-mcast detail 
===============================================================================
 BGP Router ID:192.0.2.1        AS:64501       Local AS:64501      
===============================================================================
 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 EVPN Inclusive-Mcast Routes
===============================================================================
Original Attributes
  
Network        : n/a
Nexthop        : 192.0.2.4
From           : 192.0.2.4
Res. Nexthop   : n/a
Local Pref.    : n/a                    Interface Name : NotAvailable
Aggregator AS  : None                   Aggregator     : None
Atomic Aggr.   : Not Atomic             MED            : None
AIGP Metric    : None                   IGP Cost       : 0
Connector      : None
Community      : target:64502:1 bgp-tunnel-encap:MPLS
Cluster        : No Cluster Members
Originator Id  : None                   Peer Router Id : 192.0.2.4
Flags          : Used Valid Best IGP 
Route Source   : External
AS-Path        : 64502 
EVPN type      : INCL-MCAST             
Tag            : 0                      
Originator IP  : 192.0.2.4
Route Dist.    : 192.0.2.4:1
Route Tag      : 0                      
Neighbor-AS    : 64502
Orig Validation: N/A                    
Source Class   : 0                      Dest Class     : 0
Add Paths Send : Default                
Last Modified  : 00h01m57s              
-------------------------------------------------------------------------------
PMSI Tunnel Attributes : 
Tunnel-type    : Ingress Replication    
Flags          : Type: RNVE(0) BM: 0 U: 0 Leaf: not required
MPLS Label     : LABEL 524284           
Tunnel-Endpoint: 192.0.2.4
-------------------------------------------------------------------------------
---snip---

PE-4 has received an IMET-P2MP-IR route sent by root node PE-1, as follows:

*A:PE-4# show router bgp routes evpn incl-mcast detail 
===============================================================================
 BGP Router ID:192.0.2.4        AS:64502       Local AS:64502      
===============================================================================
 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 EVPN Inclusive-Mcast Routes
===============================================================================
Original Attributes
  
Network        : n/a
Nexthop        : 192.0.2.1
From           : 192.0.2.1
Res. Nexthop   : n/a
Local Pref.    : n/a                    Interface Name : NotAvailable
Aggregator AS  : None                   Aggregator     : None
Atomic Aggr.   : Not Atomic             MED            : None
AIGP Metric    : None                   IGP Cost       : 0
Connector      : None
Community      : target:64501:1 bgp-tunnel-encap:MPLS
Cluster        : No Cluster Members
Originator Id  : None                   Peer Router Id : 192.0.2.1
Flags          : Used Valid Best IGP 
Route Source   : External
AS-Path        : 64501 
EVPN type      : INCL-MCAST             
Tag            : 0                      
Originator IP  : 192.0.2.1
Route Dist.    : 192.0.2.1:1
Route Tag      : 0                      
Neighbor-AS    : 64501
Orig Validation: N/A                    
Source Class   : 0                      Dest Class     : 0
Add Paths Send : Default                
Last Modified  : 00h01m59s              
-------------------------------------------------------------------------------
PMSI Tunnel Attributes : 
Tunnel-type    : Composite LDP P2MP IR  
Flags          : Type: RNVE(0) BM: 0 U: 0 Leaf: not required
MPLS Label1 Ag : LABEL 0                
MPLS Label2 IR : LABEL 524284           
Root-Node      : 192.0.2.1              LSP-ID         : 8193
-------------------------------------------------------------------------------
---snip---

When leaf node PE-4 receives this IMET-P2MP-IR route, a provider tunnel is established toward the root. One P2MP LDP binding of opaque type GRT recursive is active on PE-4:

*A:PE-4# show router ldp bindings active p2mp summary ipv4 
 No. of Generic IPv4 P2MP Active Bindings: 0
 No. of In-Band-SSM IPv4 P2MP Active Bindings: 0
 No. of In-Band-VPN-SSM IPv4 P2MP Active Bindings: 0
 No. of In-Band-SSM IPv4 P2MP Active Bindings: 0
 No. of VPN Recursive with Generic IPv4 P2MP Active Bindings: 0
 No. of GRT Recursive with Generic IPv4 P2MP Active Bindings: 1

The following GRT recursive P2MP LDP binding with root P-3 and inner root PE-1 is active on PE-4:

*A:PE-4# show router ldp bindings active p2mp opaque-type grt-recursive ipv4 
 
===============================================================================
LDP Bindings (IPv4 LSR ID 192.0.2.4)
             (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
===============================================================================
LDP GRT Recursive with Generic IPv4 P2MP Bindings (Active)
===============================================================================
P2MP-Id                                      
InnerRootAddr                               Interface
RootAddr                                    Op
IngLbl                                      EgrLbl
EgrNH                                       EgrIf/LspId
-------------------------------------------------------------------------------
8193
192.0.2.1                                   73728
192.0.2.3                                   Pop
524283                                        --
  --                                          --
                                              
-------------------------------------------------------------------------------
No. of GRT Recursive with Generic IPv4 P2MP Active Bindings: 1
===============================================================================

The following detailed output shows that the P2MP type is 7:

*A:PE-4# show router ldp bindings active p2mp opaque-type grt-recursive ipv4 detail 
 
===============================================================================
LDP Bindings (IPv4 LSR ID 192.0.2.4)
             (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
==============================================================================
LDP GRT Recursive with Generic IPv4 P2MP Bindings (Active)
==============================================================================
-------------------------------------------------------------------------------
P2MP Type      : 7                  P2MP-Id    : 8193
Root-Addr      : 192.0.2.3
InnerRoot-Addr : 192.0.2.1
-------------------------------------------------------------------------------
Op             : Pop                
Ing Lbl        : 524283             
Egr Lbl        :   --               
Egr Int/LspId  :   --
EgrNextHop     :   --
Egr. Flags     : None               Ing. Flags : None
===============================================================================
No. of GRT Recursive with Generic IPv4 P2MP Active Bindings: 1
==============================================================================

P-3 has two P2MP LDP bindings active: one toward the—downstream—lower FEC (LF) PE-4 and another to the—upstream—upper FEC (UF) P-2, as follows. Both P2MP LDP bindings have inner root 192.0.2.1 and they are stitched to each other.

*A:P-3# show router ldp bindings active p2mp opaque-type grt-recursive ipv4 
 
===============================================================================
LDP Bindings (IPv4 LSR ID 192.0.2.3)
             (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
===============================================================================
LDP GRT Recursive with Generic IPv4 P2MP Bindings (Active)
===============================================================================
P2MP-Id                                      
InnerRootAddr                               Interface
RootAddr                                    Op
IngLbl                                      EgrLbl
EgrNH                                       EgrIf/LspId
-------------------------------------------------------------------------------
8193
192.0.2.1                                   Unknw
192.0.2.3 (LF)                              Push
  --                                        524283
192.168.34.2                                1/1/1
                                             
8193
192.0.2.1                                   Unknw
192.168.23.1 (UF)                           Swap
524279                                      Stitched
  --                                          --
                                             
-------------------------------------------------------------------------------
No. of GRT Recursive with Generic IPv4 P2MP Active Bindings: 2
===============================================================================

P-2 has two P2MP LDP bindings active: one GRT recursive (type 7) and one generic (type 1), as follows:

*A:P-2# show router ldp bindings active p2mp summary ipv4 
 No. of Generic IPv4 P2MP Active Bindings: 1
 No. of In-Band-SSM IPv4 P2MP Active Bindings: 0
 No. of In-Band-VPN-SSM IPv4 P2MP Active Bindings: 0
 No. of In-Band-SSM IPv4 P2MP Active Bindings: 0
 No. of VPN Recursive with Generic IPv4 P2MP Active Bindings: 0
 No. of GRT Recursive with Generic IPv4 P2MP Active Bindings: 1

On P-2, the GRT recursive P2MP LDP binding with inner root 192.0.2.1 is toward LF P-3, as follows:

*A:P-2# show router ldp bindings active p2mp opaque-type grt-recursive ipv4 
 
===============================================================================
LDP Bindings (IPv4 LSR ID 192.0.2.2)
             (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
===============================================================================
LDP GRT Recursive with Generic IPv4 P2MP Bindings (Active)
===============================================================================
P2MP-Id                                      
InnerRootAddr                               Interface
RootAddr                                    Op
IngLbl                                      EgrLbl
EgrNH                                       EgrIf/LspId
-------------------------------------------------------------------------------
8193
192.0.2.1                                   Unknw
192.168.23.1 (LF)                           Push
  --                                        524279
192.168.23.2                                1/1/1
                                             
-------------------------------------------------------------------------------
No. of GRT Recursive with Generic IPv4 P2MP Active Bindings: 1
===============================================================================

On P-2, the generic P2MP LDP binding is toward UF PE-1, as follows. The UF has root address 192.0.2.1 and is stitched to the LF with inner root address 192.0.2.1.

*A:P-2# show router ldp bindings active p2mp opaque-type generic ipv4 
 
===============================================================================
LDP Bindings (IPv4 LSR ID 192.0.2.2)
             (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
===============================================================================
LDP Generic IPv4 P2MP Bindings (Active)
===============================================================================
P2MP-Id                                     Interface
RootAddr                                    Op
IngLbl                                      EgrLbl
EgrNH                                       EgrIf/LspId
-------------------------------------------------------------------------------
8193                                        Unknw
192.0.2.1 (UF)                              Swap
524279                                      Stitched
  --                                          --
                                              
-------------------------------------------------------------------------------
No. of Generic IPv4 P2MP Active Bindings: 1
===============================================================================

PE-1 has one P2MP LDP active binding toward LF P-2 (type 1- generic):

*A:PE-1# show router ldp bindings active p2mp opaque-type generic ipv4 
 
===============================================================================
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
===============================================================================
LDP Generic IPv4 P2MP Bindings (Active)
===============================================================================
P2MP-Id                                     Interface
RootAddr                                    Op
IngLbl                                      EgrLbl
EgrNH                                       EgrIf/LspId
-------------------------------------------------------------------------------
8193                                        73728
192.0.2.1                                   Push
  --                                        524279
192.168.12.2                                1/1/1
                                             
-------------------------------------------------------------------------------
No. of Generic IPv4 P2MP Active Bindings: 1
===============================================================================

The EVPN BUM traffic is forwarded from the root node PE-1 to the leaf node PE-4 over the P2MP tree. The following command on root node PE-1 shows that an EVPN destination (that uses a BGP tunnel) toward leaf node PE-4 is established, and can carry multicast traffic (BUM):

*A:PE-1# show service id 1 evpn-mpls 
 
===============================================================================
BGP EVPN-MPLS Dest
===============================================================================
TEP Address     Egr Label     Num. MACs   Mcast           Last Change
                Transport:Tnl                             Sup BCast Domain
-------------------------------------------------------------------------------
192.0.2.4       524284        0           bum             06/02/2021 08:31:14
                bgp:262146                                No
-------------------------------------------------------------------------------
Number of entries : 1
-------------------------------------------------------------------------------
===============================================================================
---snip---

The provider tunnel in VPLS 1 is established using LDP and the operational state is up, as follows. The router will always use the provider tunnel and not the EVPN-MPLS destination, as long as the provider tunnel Oper State is up:

*A:PE-1# show service id 1 provider-tunnel 
 
===============================================================================
Service Provider Tunnel Information
===============================================================================
Type               : inclusive          Root and Leaf      : enabled
Admin State        : enabled            Data Delay Intvl   : 15 secs
PMSI Type          : ldp                LSP Template       : 
Remain Delay Intvl : 0 secs             LSP Name used      : 8193
PMSI Owner         : bgpEvpnMpls        
Oper State         : up                 Root Bind Id       : 32767
===============================================================================

The following SDP of type VplsPmsi is auto-created in VPLS 1 on root node PE-1:

*A:PE-1# show service id 1 sdp 
 
===============================================================================
Services: Service Destination Points
===============================================================================
SdpId            Type     Far End addr    Adm     Opr       I.Lbl     E.Lbl
-------------------------------------------------------------------------------
32767:4294967294 VplsPmsi not applicable  Up      Up        None      3
-------------------------------------------------------------------------------
Number of SDPs : 1
-------------------------------------------------------------------------------
===============================================================================

The following tools dump command shows the originating provider tunnels for VPLS 1 on root node PE-1:

*A:PE-1# tools dump service id 1 provider-tunnels type originating 
 
===============================================================================
VPLS 1 Inclusive Provider Tunnels Originating             
===============================================================================
ipmsi (LDP)                                     P2MP-ID  Root-Addr
-------------------------------------------------------------------------------
8193                                            8193    192.0.2.1       
 
-------------------------------------------------------------------------------

The following command shows the terminating provider tunnels for VPLS 1 on leaf node PE-4:

*A:PE-4# tools dump service id 1 provider-tunnels type terminating 
 
===============================================================================
VPLS 1 Inclusive Provider Tunnels Terminating             
===============================================================================
ipmsi (LDP)                                     P2MP-ID  Root-Addr
-------------------------------------------------------------------------------
                                                8193    192.0.2.1       
 
-------------------------------------------------------------------------------

Optimized Inter-AS Model C for mLDP

When some leaf nodes do not support labeled BGP routes or recursive opaque mLDP label mapping, the ASBR in the AS where the leaf nodes are situated needs to leak the root IP address into the leaf PE IGP, which allows the leaf node PE-4 to send a generic FEC type 1 to join the root. The recursive opaque functionality is pushed to the local ASBR P-3.

Example topology for optimized Inter-AS Model C for mLDP shows the example topology for the optimized inter-AS model C for mLDP.

Figure 2. Example topology for optimized Inter-AS Model C for mLDP

The configuration starts with the configuration in the preceding section Inter-AS Model C for mLDP. The policy to export system prefixes from the ASs to labeled BGP is already configured and applied on both ASBRs. The following additional policies are defined on ASBR P-3 in the AS of the leaf node to export labeled BGP routes to OSPF and to LDP.

# on ASBR P-3:
configure
    router
        policy-options
            begin
            policy-statement "bgpToOspf"
                entry 10
                    from
                        protocol bgp-label
                    exit
                    to
                        protocol ospf
                    exit
                    action accept
                    exit
                exit
            exit
            policy-statement "bgpToLdp"
                entry 10
                    from
                        protocol bgp-label
                    exit
                    to
                        protocol ldp
                    exit
                    action accept
                    exit
                exit
            exit
            commit

Policy "bgpToOspf" is configured in the OSPF context and policy "bgpToLdp" in the ldp context, as follows:

# on ASBR P-3:
configure
    router Base
        ospf 
            export "bgpToOspf"
        exit
        ldp 
            export-tunnel-table "bgpToLdp"
        exit

Optimized Inter-AS Model C for mLDP - Verification

The prefixes from AS 64501 are now exported to OSPF and LDP in AS 64502; therefore, leaf node PE-4 will no longer use the labeled BGP routes to a node in AS 64501.

*A:PE-4# show router bgp routes label-ipv4 
===============================================================================
 BGP Router ID:192.0.2.4        AS:64502       Local AS:64502      
===============================================================================
 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 Routes
===============================================================================
Flag  Network                                            LocalPref   MED
      Nexthop (Router)                                   Path-Id     IGP Cost
      As-Path                                                        Label
-------------------------------------------------------------------------------
*i    192.0.2.1/32                                       100         10
      192.0.2.3                                          None        10
      64501                                                          524283
*i    192.0.2.2/32                                       100         None
      192.0.2.3                                          None        10
      64501                                                          524282
-------------------------------------------------------------------------------
Routes : 2
===============================================================================

The following route table in PE-4 shows that an OSPF route exists toward prefix 192.0.2.1:

*A:PE-4# show router route-table 192.0.2.1 
 
===============================================================================
Route Table (Router: Base)
===============================================================================
Dest Prefix[Flags]                            Type    Proto     Age        Pref
      Next Hop[Interface Name]                                    Metric   
-------------------------------------------------------------------------------
192.0.2.1/32                                  Remote  OSPF      00h00m21s  150
       192.168.34.1                                                 10
-------------------------------------------------------------------------------
No. of Routes: 1
Flags: n = Number of times nexthop is repeated
       B = BGP backup route available
       L = LFA nexthop available
       S = Sticky ECMP requested
===============================================================================

On PE-4, all tunnels are LDP tunnels; no BGP tunnels are established from PE-4 to PE-1 and P-2, as follows:

*A:PE-4# show router tunnel-table 
 
===============================================================================
IPv4 Tunnel Table (Router: Base)
===============================================================================
Destination           Owner     Encap TunnelId  Pref   Nexthop        Metric
   Color                                                              
-------------------------------------------------------------------------------
192.0.2.1/32          ldp       MPLS  65538     9      192.168.34.1   10
192.0.2.2/32          ldp       MPLS  65539     9      192.168.34.1   1
192.0.2.3/32          ldp       MPLS  65537     9      192.168.34.1   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 all other nodes, the route table and tunnel table are the same as in the non-optimized scenario. The route table and the tunnel table for ASBR P-3 are as follows:

*A:P-3# show router route-table protocol bgp-label 
 
===============================================================================
Route Table (Router: Base)
===============================================================================
Dest Prefix[Flags]                            Type    Proto     Age        Pref
      Next Hop[Interface Name]                                    Metric   
-------------------------------------------------------------------------------
192.0.2.1/32                                  Remote  BGP_LABEL 00h10m48s  170
       192.168.23.1                                                 0
192.0.2.2/32                                  Remote  BGP_LABEL 00h10m48s  170
       192.168.23.1                                                 0
-------------------------------------------------------------------------------
No. of Routes: 2
Flags: n = Number of times nexthop is repeated
       B = BGP backup route available
       L = LFA nexthop available
       S = Sticky ECMP requested
===============================================================================
*A:P-3# show router tunnel-table 
 
===============================================================================
IPv4 Tunnel Table (Router: Base)
===============================================================================
Destination           Owner     Encap TunnelId  Pref   Nexthop        Metric
   Color                                                              
-------------------------------------------------------------------------------
192.0.2.1/32          bgp       MPLS  262145    12     192.168.23.1   1000
192.0.2.2/32          bgp       MPLS  262146    12     192.168.23.1   1000
192.0.2.4/32          ldp       MPLS  65537     9      192.168.34.2   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
===============================================================================

Root node PE-1 will send an IMET-P2MP-IR route to leaf node PE-4. PE-4 will send an mLDP label mapping message type 1 instead of type 7, because there is an LDP tunnel toward PE-1 instead of a BGP tunnel. The only P2MP mLDP binding on leaf node PE-4 is a generic P2MP binding, as follows:

*A:PE-4# show router ldp bindings p2mp summary ipv4 
 No. of Generic IPv4 P2MP Bindings: 1
 No. of In-Band-SSM IPv4 P2MP Bindings: 0
 No. of In-Band-VPN-SSM IPv4 P2MP Bindings: 0
 No. of Recursive with In-Band-SSM IPv4 P2MP Bindings: 0
 No. of VPN Recursive with Generic IPv4 P2MP Bindings: 0
 No. of GRT Recursive with Generic IPv4 P2MP Bindings: 0

PE-4 sends the following mLDP label mapping message type 1 with root address 192.0.2.1 (PE-1) to its peer P-3.

15 2021/06/02 08:39:21.702 UTC MINOR: DEBUG #2001 Base LDP
"LDP: LDP
Send Label Mapping packet (msgId 100) to 192.0.2.3:0
Protocol version = 1
Label 524279 advertised for the following FECs
P2MP: root = 192.0.2.1, T: 1, L: 4, TunnelId: 8193
"

The following generic P2MP mLDP binding for root address 192.0.2.1 is seen on PE-4:

*A:PE-4# show router ldp bindings p2mp opaque-type generic detail ipv4 
 
===============================================================================
LDP Bindings (IPv4 LSR ID 192.0.2.4)
             (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
==============================================================================
LDP Generic IPv4 P2MP Bindings
==============================================================================
-------------------------------------------------------------------------------
P2MP Type      : 1                  P2MP-Id    : 8193
Root-Addr      : 192.0.2.1
-------------------------------------------------------------------------------
Peer           : 192.0.2.3:0
Ing Lbl        : 524279U            
Egr Lbl        :   --               
Egr Int/LspId  :   --
EgrNextHop     :   --
Egr. Flags     : None               Ing. Flags : None
===============================================================================
No. of Generic IPv4 P2MP Bindings: 1
==============================================================================

ASBR P-3 receives the generic P2MP mLDP label mapping message from PE-4 (T: 1) and resolves the root node 192.0.2.1 to next-hop P-2. P-3 sends a GRT recursive P2MP mLDP label mapping message (T: 7) with inner root 192.0.2.1 to its peer P-2 (root 192.168.23.1) in AS 64501:

25 2021/06/02 08:39:21.696 UTC MINOR: DEBUG #2001 Base LDP
"LDP: LDP
Recv Label Mapping packet (msgId 100) from 192.0.2.4:0
Protocol version = 1
Label 524279 advertised for the following FECs
P2MP: root = 192.0.2.1, T: 1, L: 4, TunnelId: 8193
"
26 2021/06/02 08:39:21.696 UTC MINOR: DEBUG #2001 Base LDP
"LDP: LDP
Send Label Mapping packet (msgId 81) to 192.168.23.1:0
Protocol version = 1
Label 524278 advertised for the following FECs
P2MP: root = 192.168.23.1, T: 7, L: 17 (InnerRoot: 192.0.2.1 T: 1, L: 4, TunnelId: 8193)
"
*A:P-3# show router ldp bindings p2mp opaque-type generic detail ipv4 
 
===============================================================================
LDP Bindings (IPv4 LSR ID 192.0.2.3)
             (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
==============================================================================
LDP Generic IPv4 P2MP Bindings
==============================================================================
-------------------------------------------------------------------------------
P2MP Type      : 1                  P2MP-Id    : 8193
Root-Addr      : 192.0.2.1 (LF)
-------------------------------------------------------------------------------
Peer           : 192.0.2.4:0
Ing Lbl        :   --               
Egr Lbl        : 524279             
Egr Int/LspId  : 1/1/1
EgrNextHop     : 192.168.34.2
Egr. Flags     : None               Ing. Flags : None
Egr If Name    : int-P-3-PE-4
Metric         : 1                  Mtu        : 1564
===============================================================================
No. of Generic IPv4 P2MP Bindings: 1
==============================================================================
*A:P-3# show router ldp bindings p2mp opaque-type grt-recursive detail ipv4 
 
===============================================================================
LDP Bindings (IPv4 LSR ID 192.0.2.3)
             (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
==============================================================================
LDP GRT Recursive with Generic IPv4 P2MP Bindings
==============================================================================
-------------------------------------------------------------------------------
P2MP Type      : 7                  P2MP-Id    : 8193
Root-Addr      : 192.168.23.1 (UF)
InnerRoot-Addr : 192.0.2.1
-------------------------------------------------------------------------------
Peer           : 192.168.23.1:0
Ing Lbl        : 524278U            
Egr Lbl        :   --               
Egr Int/LspId  :   --
EgrNextHop     :   --
Egr. Flags     : None               Ing. Flags : None
===============================================================================
No. of GRT Recursive with Generic IPv4 P2MP Bindings: 1
==============================================================================

The P2MP mLDP bindings on P-2 and PE-1 are the same as in the previous non-optimized inter-AS model C for mLDP scenario. P-2 has one GRT recursive mLDP binding to P-3 and one generic mLDP binding to root node PE-1, whereas PE-1 only has a generic mLDP binding to P-2.

The following command on root node PE-1 shows that an EVPN-MPLS destination is created to the leaf node PE-4. This EVPN destination runs over a BGP tunnel and can transport multicast (BUM) traffic. However, as discussed in the preceding section, the EVPN destination is used for BUM traffic only in the case where the provider tunnel goes operationally down.

*A:PE-1# show service id 1 evpn-mpls 
 
===============================================================================
BGP EVPN-MPLS Dest
===============================================================================
TEP Address     Egr Label     Num. MACs   Mcast           Last Change
                Transport:Tnl                             Sup BCast Domain
-------------------------------------------------------------------------------
192.0.2.4       524284        0           bum             06/02/2021 08:31:14
                bgp:262146                                No
-------------------------------------------------------------------------------
Number of entries : 1
-------------------------------------------------------------------------------
===============================================================================
---snip---

The same command on the leaf node PE-4 shows an EVPN destination running on an LDP tunnel instead of a BGP tunnel. This destination is used whenever PE-4 needs to send BUM traffic to PE-1:

*A:PE-4# show service id 1 evpn-mpls 
 
===============================================================================
BGP EVPN-MPLS Dest
===============================================================================
TEP Address     Egr Label     Num. MACs   Mcast           Last Change
                Transport:Tnl                             Sup BCast Domain
-------------------------------------------------------------------------------
192.0.2.1       524284        0           bum             06/02/2021 08:31:14
                ldp:65538                                 No
-------------------------------------------------------------------------------
Number of entries : 1
-------------------------------------------------------------------------------
===============================================================================
---snip--- 

The other show commands in the Inter-AS Model C for mLDP section have an identical output for both scenarios.

Conclusion

P2MP mLDP is supported in inter-AS model C for EVPN-MPLS services with or without optimization. Optimization in this chapter refers to the ability to set up an end-to-end mLDP tunnel without the need for recursive opaque mLDP FECs on the leaf nodes. A similar configuration is applied in the case of seamless MPLS across different areas.