6PE: Crossing Multiple AS
6PE: Crossing Multiple AS
RFC 4798 describes three approaches to provide communication between two IPv6 islands connected to two different BGP Autonomous Systems (AS).
These approaches are-
- eBGP redistribution of IPv6 routes from AS to neighboring AS
- eBGP redistribution of labeled IPv6 routes from AS to neighboring AS
- Multihop eBGP redistribution of labeled IPv6 routes between source and destination ASes, with eBGP redistribution of labeled IPv4 routes from AS to neighboring AS.
Network topology:
Approach 2:
The 6PE1 router has iBGP peering with ASBR-1 router in AS 100 and redistribute labeled IPv6 prefixes to ASBR-1 router. The ASBR-1 router then uses eBGP to redistribute non-labeled IPv6 prefixes to neighboring ASBR-2 router in AS 200, which in turn distributes them to 6PE2 router.
The inter-ASBR link is IPv6 enabled and each connected interface has an IPv6 address. There is no LSP between ASBRs.
MP-BGP Configuration on 6PE routers:
6PE1 and 6PE2 routers run eBGP session with CE1 and CE2 routers respectively. 6PE1 router also runs iBGP session with ASBR-1 router in AS 100. 6PE2 router runs iBGP session with ASBR-2 router in AS 200. ASBR-1 and ASBR-2 router also run an eBGP connection between them.
BGP Configuration on 6PE1
ipv6 unicast-routing
ipv6 cef
!
mpls label protocol ldp
mpls ldp router-id Loopback 0 force
mpls ipv6 source-interface Loopback 0
!
interface Loopback 0
ip address 1.1.1.1 255.255.255.255
ipv6 address ABCD::1/128
!
router bgp 100
neighbor 2001:1::1 remote-as 65101
neighbor 2001:1::1 description eBGP with CE1 router
neighbor 3.3.3.3 remote-as 100
neighbor 3.3.3.3 description iBGP with ASBR-1 router
neighbor 3.3.3.3 update-source Loopback 0
!
address-family ipv6
neighbor 2001:1::1 activate
neighbor 3.3.3.3 activate
neighbor 3.3.3.3 send-label
redistribute connected
exit-address-family
!
BGP Configuration on ASBRs
ASBR-1 router:
ipv6 unicast-routing
ipv6 cef
!
mpls label protocol ldp
mpls ldp router-id Loopback 0 force
mpls ipv6 source-interface Loopback 0
!
interface Loopback 0
ip address 3.3.3.3 255.255.255.255
ipv6 address ABCD::3/128
!
router bgp 100
neighbor 1.1.1.1 remote-as 100
neighbor 1.1.1.1 description iBGP with 6PE1 router
neighbor 2001:3::2 remote-as 200
neighbor 2001:3::2 description eBGP with ASBR-2 router
!
address-family ipv6
neighbor 1.1.1.1 activate
neighbor 1.1.1.1 send-label
neighbor 2001:3::2 activate
redistribute connected
exit-address-family
!
ASBR-2 router:
ipv6 unicast-routing
ipv6 cef
!
mpls label protocol ldp
mpls ldp router-id Loopback 0 force
mpls ipv6 source-interface Loopback 0
!
interface Loopback 0
ip address 4.4.4.4 255.255.255.255
ipv6 address ABCD::4/128
!
router bgp 200
neighbor 2001:3::1 remote-as 100
neighbor 2001:3::1 description eBGP with ASBR-1 router
neighbor 6.6.6.6 remote-as 200
neighbor 6.6.6.6 description iBGP with 6PE2 router
neighbor 6.6.6.6 update-source Loopback 0
!
address-family ipv6
neighbor 2001:3::1 activate
neighbor 6.6.6.6 activate
neighbor 6.6.6.6 send-label
redistribute connected
exit-address-family
!
BGP Configuration on 6PE2
ipv6 unicast-routing
ipv6 cef
!
mpls label protocol ldp
mpls ldp router-id Loopback 0 force
mpls ipv6 source-interface Loopback 0
!
interface Loopback 0
ip address 6.6.6.6 255.255.255.255
ipv6 address ABCD::6/128
!
router bgp 200
neighbor 4.4.4.4 remote-as 200
neighbor 4.4.4.4 description iBGP with ASBR-2 router
neighbor 4.4.4.4 update-source Loopback 0
neighbor 2001:2::1 remote-as 65102
neighbor 2001:2::1 description eBGP with CE2 router
!
address-family ipv6
neighbor 4.4.4.4 activate
neighbor 4.4.4.4 send-label
neighbor 2001:2::1 activate
redistribute connected
exit-address-family
!
6PE1 router advertises a label for its connected IPv6 networks to ASBR-1 router via BGP. The following output shows IPv6 prefixes with their labels. IPv6 prefixes 2001:1::/124 and ABCD::1/128 are advertised by 6PE1 router. The next-hop for these IPv6 prefixes is the IPv4-mapped IPv6 address ::FFFF:1.1.1.1 of 6PE1 router. The In Label/Out Label for IPv6 prefix 2001:1::/124 is No Label/20. This indicates that there is no LSP between ASBR-1 and ASBR-2 router, because ASBR-1 router imposes label 20 if packets are destined for 2001:1::/124 network with next-hop as 6PE1 router.
IPv6 Prefixes and labels on ASBR-1
ASBR-1# show bgp ipv6 unicast labels
Network Next Hop In label/Out label
2001:1::/124 ::FFFF:1.1.1.1 nolabel/20
2001:3::/124 2001:3::2 21/nolabel
:: 21/nolabel
ABCD::1/128 ::FFFF:1.1.1.1 nolabel/19
ABCD::3/128 :: 19/nolabel
ABCD::4/128 2001:3::2 20/nolabel
ABCD::6/128 2001:3::2 22/nolabel
Similarly, on ASBR-2 router, the In Label/Out Label for IPv6 prefix 2001:1::/124 is 23/No Label. This also indicates that there is no LSP between ASBR-2 and ASBR-1 router as the Out Label is No Label. However, the In Label is Label 23 which it will advertise to 6PE2 router via BGP.
IPv6 Prefixes and labels on ASBR-2
ASBR-2# show bgp ipv6 unicast labels
Network Next Hop In label/Out label
2001:1::/124 2001:3::1 23/nolabel
2001:3::/124 :: 20/nolabel
2001:3::1 20/nolabel
ABCD::1/128 2001:3::1 22/nolabel
ABCD::3/128 2001:3::1 21/nolabel
ABCD::4/128 :: 19/nolabel
ABCD::6/128 ::FFFF:6.6.6.6 nolabel/19
The following output shows the labels that will be imposed by 6PE2 router to reach IPv6 prefix 2001:1::/124 connected to 6PE1 and CE1 routers. The top label Label 16 is the IGP label while the bottom Label 23 is the BGP VPNv4 label advertised by ASBR-2 router.
Labels imposed by 6PE2
6PE2# show bgp ipv6 unicast labels
Network Next Hop In label/Out label
2001:1::/124 ::FFFF:4.4.4.4 nolabel/23
2001:3::/124 ::FFFF:4.4.4.4 nolabel/20
ABCD::1/128 ::FFFF:4.4.4.4 nolabel/22
ABCD::3/128 ::FFFF:4.4.4.4 nolabel/21
ABCD::4/128 ::FFFF:4.4.4.4 nolabel/19
ABCD::6/128 :: 19/nolabel
6PE2# show ip cef 4.4.4.4
4.4.4.4/32, version 12, epoch 0, cached adjacency 10.2.2.5
0 packets, 0 bytes
tag information set
local tag: 17
fast tag rewrite with Fa0/0, 10.2.2.5, tags imposed: {16}
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: {16}
6PE2# show ipv6 cef 2001:1::
2001:1::/124
nexthop ::FFFF:4.4.4.4
fast tag rewrite with Fa0/0, 10.2.2.5, tags imposed: {16 23}