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 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:
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
