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6PE with iBGP - IOS-XR example

6PE Overview

The Cisco 6PE solution enables IPv6 domains to communicate with each other over an MPLS IPv4 core network. MP-BGP in the IPv4 network is used to exchange IPv6 reachability information along with a label for each IPv6 prefix announced. 6PE routers are dual-stack routers i.e. running IPv6 with the customers and IPv4 in the core.

6PE routers do the following:

  • Participate in V4 IGP to establish internal reachability inside the MPLS cloud
  • Participate in LDP for binding V4 labels
  • Run MP-BGP4 (Multi-Protocol iBGP) to advertise v6 reachability and distribute V6 labels among them

The labels can be distributed as follows:

Per-Prefix label - The 6PE node distributes labels for each IPv6 prefix learnt from interfaces connected to CE routers

  • Run IPv6 routing protocols (eBGP6, Static, ISIS v6, OSPF v3 , EIGRP v6, iBGP) with CE routers to advertise V6 reachability learnt from their peers over the MPLS cloud
  • IGP protocol between CE to PE has to be redistributed into MP-iBGP for end to end reachability


6PE with iBGP between CE and PE

6PE with iBGP between PE and CE is supported since IOS-XR 4.0. Unlike IOS an important mandatory configuration command is required in IOS-XR. It is required to configure "ibgp policy out enforce-modifications" under router bgp <AS>  to allow changing attributes on the RR for reflected routes.

The following is serving as example:


Screen Shot 2013-10-17 at 11.32.29.png

Configuration of PE-1(RR):

router bgp 1

bgp router-id 192.168.0.2

ibgp policy out enforce-modifications

address-family ipv4 unicast

!

address-family ipv6 unicast

  allocate-label all

!

neighbor 2001:12::2

  remote-as 1

  description iBGP peer to CE-A

  address-family ipv6 unicast

   route-policy pass-all in

   route-reflector-client

   route-policy pass-all out

  !

!

neighbor 192.168.0.1

  remote-as 1

  description iBGP peer to P2

  update-source Loopback0

  address-family ipv6 labeled-unicast

   route-policy pass-all in

   route-policy pass-all out

   next-hop-self

  !

!

!

Example prefix received from the RRC CE-A:

RP/0/0/CPU0:PE-1#show bgp ipv6 labeled-unicast 65:26::1:0/112

Thu Oct 17 17:00:29.950 UTC

BGP routing table entry for 65:26::1:0/112

Versions:

  Process           bRIB/RIB  SendTblVer

  Speaker                  3           3

    Local Label: 16005

Last Modified: Oct 17 15:35:29.659 for 01:25:00

Paths: (1 available, best #1)

  Advertised to peers (in unique update groups):

    192.168.0.1    

  Path #1: Received by speaker 0

  Advertised to peers (in unique update groups):

    192.168.0.1    

  Local, (Received from a RR-client)

    2001:12::2 from 2001:12::2 (192.168.0.4)

      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best, import-candidate

      Received Path ID 0, Local Path ID 1, version 3

RP/0/0/CPU0:PE-2#sh bgp ipv6 labeled-unicast 65:26::1:0/112

Thu Oct 17 16:57:18.393 UTC

BGP routing table entry for 65:26::1:0/112

Versions:

  Process           bRIB/RIB  SendTblVer

  Speaker                  3           3

Last Modified: Oct 17 16:36:20.733 for 00:20:57

Paths: (1 available, best #1)

  Advertised to peers (in unique update groups):

    2001:10::2                             

  Path #1: Received by speaker 0

  Advertised to peers (in unique update groups):

    2001:10::2                             

  Local

    192.168.0.2 (metric 1) from 192.168.0.2 (192.168.0.4)

      Received Label 16005

      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best, import-candidate

      Received Path ID 0, Local Path ID 1, version 3

      Originator: 192.168.0.4, Cluster list: 192.168.0.2

RP/0/0/CPU0:CE-B#sh bgp ipv6 unicast 65:26::1:0/112

Thu Oct 17 17:28:51.253 UTC

BGP routing table entry for 65:26::1:0/112

Versions:

  Process           bRIB/RIB  SendTblVer

  Speaker                  3           3

Last Modified: Oct 17 17:28:45.753 for 00:00:05

Paths: (1 available, best #1)

  Not advertised to any peer

  Path #1: Received by speaker 0

  Not advertised to any peer

  Local

    192.168.0.2 from 2001:10::1 (192.168.0.4)

      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best, import-candidate

      Received Path ID 0, Local Path ID 1, version 3

      Originator: 192.168.0.4, Cluster list: 192.168.0.1, 192.168.0.2

RP/0/0/CPU0:RR-client-B#show route ipv6

Thu Oct 17 17:29:15.082 UTC

Codes: C - connected, S - static, R - RIP, B - BGP, (>) - Diversion path

       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

       i - ISIS, L1 - IS-IS level-1, L2 - IS-IS level-2

       ia - IS-IS inter area, su - IS-IS summary null, * - candidate default

       U - per-user static route, o - ODR, L - local, G  - DAGR

       A - access/subscriber, a - Application route, - FRR Backup path

Gateway of last resort is not set

B    65:26::1:0/112

      [200/0] via ::ffff:192.168.0.2 (nexthop in vrf default), 00:00:28

C    2001:10::/64 is directly connected,

      00:36:38, GigabitEthernet0/0/0/0

L    2001:10::2/128 is directly connected,

      00:36:38, GigabitEthernet0/0/0/0

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