6PE: Crossing Multiple AS - Part 2
6PE: Crossing Multiple AS - Part 2
Approach 3:
In the approach, IPv6 prefixes are not maintained or distributed by ASBR routers. The ASBR routers are not dual-stack capable. The inter-ASBR link is IPv4 and MPLS enabled. An ASBR needs to maintain labeled IPv4 /32 routes to the 6PE routers within the AS. It uses eBGP to distribute these routes to other ASes. ASBRs also uses eBGP to pass along the labeled IPv4 /32 routes. This results in creation of LSP from 6PE1 router to 6PE2 router. Now, a multihop eBGP connection can be established between these 6PE routers and exchange IPv6 prefixes with IPv4-mapped IPv6 next-hop address.
Network topology:
Multihop eBGP connection between 6PE routers:
Multihop eBGP
6PE1 router:
router bgp 100
neighbor 6.6.6.6 remote-as 200
neighbor 6.6.6.6 update-source Loopback 0
neighbor 6.6.6.6 ebgp-multihop 10
!
address-family ipv6
neighbor 6.6.6.6 activate
neighbor 6.6.6.6 send-label
redistribute connected
exit-address-family
!
6PE2 router:
router bgp 200
neighbor 1.1.1.1 remote-as 100
neighbor 1.1.1.1 update-source Loopback 0
neighbor 1.1.1.1 ebgp-multihop 10
!
address-family ipv6
neighbor 1.1.1.1 activate
neighbor 1.1.1.1 send-label
redistribute connected
exit-address-family
!
After eBGP connection is established between 6PE routers, they exchange IPv6 prefixes with IPv4-mapped IPv6 address as the next-hop address ::FFFF:1.1.1.1 when 6PE1 router advertises IPv6 prefixes to 6PE2 router over multihop eBGP connection.
6PE1 router advertises Label 20 to 6PE2 router over eBGP for IPv6 prefix 2001:1::/124.
6PE1 router labels
6PE1# show mpls forwarding-table 2001:1::/124
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
20 Aggregate 2001:1::/124 2080
IPv6 prefix and labels on 6PE2
6PE2# show bgp ipv6 unicast labels
Network Next Hop In label/Out label
2001:1::/124 ::FFFF:1.1.1.1 nolabel/20
ABCD::1/128 ::FFFF:1.1.1.1 nolabel/19
ABCD::6/128 :: 25/nolabel
6PE2# show ip cef 1.1.1.1
1.1.1.1/32, version 15, epoch 0, cached adjacency 10.2.2.5
0 packets, 0 bytes
tag information set
local tag: 20
fast tag rewrite with Fa0/0, 10.2.2.5, tags imposed: {19}
via 10.2.2.5, FastEthernet0/0, 0 dependencies
next hop 10.2.2.5, FastEthernet0/0
valid cached adjacency
tag rewrite with Fa0/0, 10.2.2.5, tags imposed: {19}
6PE2# show ipv6 cef 2001:1::/124
2001:1::/124
nexthop ::FFFF:1.1.1.1
fast tag rewrite with Fa0/0, 10.2.2.5, tags imposed: {19 20}