Configure Inter-AS Option B for L3VPN

Provides step-by-step instructions to configure Inter-AS Option B for L3VPN, detailing necessary tasks to establish Layer 3 VPN connectivity between autonomous systems.

Establish L3VPN connectivity between two autonomous systems using Inter-AS Option B, ensuring correct routing, label distribution, and forwarding.

In an Inter-AS Option B deployment, multiple autonomous systems (AS) are interconnected to extend Layer 3 VPN services. The procedure requires configuring routing protocols, MPLS label distribution, BGP VPNv4/VPNv6 address families, VRFs, and validation via control-plane and data-plane verification.

Note

Although L3VPN Inter-AS Option B supports per-prefix mode, use per-next-hop-label mode because of resource limitations.

Before you begin

Plan the topology, including all PE, P, and ASBR devices and their interconnections.
Determine interface addressing, IS-IS implementation, LDP sessions, MP-BGP configuration, VRF details, route-targets, and appropriate label modes.
Ensure resource limitations are addressed by using per-next-hop-label mode instead of per-prefix mode when supported (due to scaling restrictions).

Follow these steps to configure and verify Inter-AS Option B for L3VPN:

Procedure

	1.	Configure PE1 for Inter-AS Option B. Example: Router# configure Router(config)# interface Loopback0 Router(config-if)# ipv4 address 192.168.255.2/32 Router(config-if)# ipv6 address 50:50:50::50/128 Router(config-if)# exit Router(config)# interface Bundle-Ether25 Router(config-if)# description interface to R4 Router(config-if)# ipv4 address 172.16.0.1 255.240.0.0 Router(config-if)# exit Router(config)# router isis access Router(config-isis)# is-type level-1 Router(config-isis)# net 49.0001.0000.0000.0050.00 Router(config-isis)# nsr Router(config-isis)# nsf ietf Router(config-isis)# log adjacency changes Router(config-isis)# address-family ipv4 unicast Router(config-isis-af)# metric-style wide Router(config-isis-af)# exit Router(config-isis)# interface Bundle-Ether25 Router(config-isis-if)# point-to-point Router(config-isis-if)# address-family ipv4 unicast Router(config-isis-if-af)# exit Router(config-isis-if)# exit Router(config-isis)# interface Loopback0 Router(config-isis-if)# point-to-point Router(config-isis-if)# address-family ipv4 unicast Router(config-isis-if-af)# exit Router(config-isis-if)# exit Router(config-isis)# exit Router(config)# mpls ldp Router(config-ldp)# interface Bundle-Ether25 Router(config-ldp-if)# exit Router(config-ldp)# exit Router(config)# vrf vrf1 Router(config-vrf)# address-family ipv4 unicast Router(config-vrf-af)# import route-target 100:1 Router(config-vrf-af)# export route-target 100:1 Router(config-vrf-af)# exit Router(config-vrf)# address-family ipv6 unicast Router(config-vrf-af)# import route-target 100:1 Router(config-vrf-af)# export route-target 100:1 Router(config-vrf-af)# exit Router(config-vrf)# exit Router(config)# router bgp 65000 Router(config-bgp)# nsr Router(config-bgp)# bgp router-id 192.168.255.2 Router(config-bgp)# bgp graceful-restart Router(config-bgp)# address-family vpnv4 unicast Router(config-bgp-af)# exit Router(config-bgp)# address-family vpnv6 unicast Router(config-bgp-af)# exit Router(config-bgp)# neighbor 10.10.10.10 Router(config-bgp-nbr)# remote-as 65000 Router(config-bgp-nbr)# update-source Loopback0 Router(config-bgp-nbr)# address-family vpnv4 unicast Router(config-bgp-nbr-af)# maximum-prefix 4500000 90 Router(config-bgp-nbr-af)# exit Router(config-bgp-nbr)# address-family vpnv6 unicast Router(config-bgp-nbr-af)# maximum-prefix 4500000 90 Router(config-bgp-nbr-af)# exit Router(config-bgp-nbr)# exit Router(config-bgp)# vrf vrf1 Router(config-bgp-vrf)# rd 100:1 Router(config-bgp-vrf)# bgp router-id 192.168.255.2 Router(config-bgp-vrf)# address-family ipv4 unicast Router(config-bgp-vrf-af)# label mode per-vrf Router(config-bgp-vrf-af)# redistribute connected Router(config-bgp-vrf-af)# exit Router(config-bgp-vrf)# address-family ipv6 unicast Router(config-bgp-vrf-af)# label mode per-vrf Router(config-bgp-vrf-af)# redistribute connected Router(config-bgp-vrf-af)# exit Router(config-bgp-vrf)# neighbor 192.0.2.12 Router(config-bgp-vrf-nbr)# remote-as 501 Router(config-bgp-vrf-nbr)# address-family ipv4 unicast Router(config-bgp-vrf-nbr-af)# route-policy pass-all in Router(config-bgp-vrf-nbr-af)# route-policy pass-all out Router(config-bgp-vrf-nbr-af)# exit Router(config-bgp-vrf-nbr)# exit Router(config-bgp-vrf)# neighbor 150:1:1::2 Router(config-bgp-vrf-nbr)# remote-as 501 Router(config-bgp-vrf-nbr)# address-family ipv6 unicast Router(config-bgp-vrf-nbr-af)# route-policy pass-all in Router(config-bgp-vrf-nbr-af)# route-policy pass-all out Router(config-bgp-vrf-nbr-af)# commit
	2.	Configure P1 for Inter-AS Option B. Example: Router# configure Router(config)# interface Loopback0 Router(config-if)# ipv4 address 172.16.0.1 255.255.255.255 Router(config-if)# exit Router(config)# interface Bundle-Ether12 Router(config-if)# description interface to ASBR1 Router(config-if)# ipv4 address 10.20.1.2 255.240.0.0 Router(config-if)# exit Router(config)# interface Bundle-Ether25 Router(config-if)# description interface to R50 Router(config-if)# ipv4 address 192.0.2.13 255.240.0.0 Router(config-if)# exit Router(config)# router isis core Router(config-isis)# is-type level-1 Router(config-isis)# net 49.0001.0000.0000.0020.00 Router(config-isis)# nsr Router(config-isis)# nsf ietf Router(config-isis)# log adjacency changes Router(config-isis)# address-family ipv4 unicast Router(config-isis-af)# metric-style wide Router(config-isis-af)# exit Router(config-isis)# interface Bundle-Ether12 Router(config-isis-if)# point-to-point Router(config-isis-if)# address-family ipv4 unicast Router(config-isis-if-af)# exit Router(config-isis-if)# exit Router(config-isis)# interface Bundle-Ether25 Router(config-isis-if)# point-to-point Router(config-isis-if)# address-family ipv4 unicast Router(config-isis-if-af)# exit Router(config-isis-if)# exit Router(config-isis)# interface Loopback0 Router(config-isis-if)# point-to-point Router(config-isis-if)# address-family ipv4 unicast Router(config-isis-if-af)# exit Router(config-isis-if)# exit Router(config-isis-if)# exit Router(config-isis)# exit Router(config)# mpls ldp Router(config-ldp)# nsr Router(config-ldp)# interface Bundle-Ether12 Router(config-ldp-if)# exit Router(config-ldp)# interface Bundle-Ether25 Router(config-ldp-if)# commit
	3.	Configure ASBR1 for Inter-AS Option B. Example: Router# configure Router(config)# interface Loopback0 Router(config-if)# ipv4 address 10.10.10.10 255.255.255.255 Router(config-if)# ipv6 address 10:10:10::10/128 Router(config-if)# exit Router(config)# interface Bundle-Ether12 Router(config-if)# description interface to 172.16.0.1 Router(config-if)# ipv4 address 10.20.1.1 255.240.0.0 Router(config-if)# monitor-session Test ethernet port-level Router(config-if-mon)# exit Router(config-if)# exit Router(config)# interface Bundle-Ether11 Router(config-if)# description interface to ASBR2 Router(config-if)# ipv4 address 10.1.0.1 255.255.255.0 Router(config-if)# exit Router(config)# router isis core Router(config-isis)# is-type level-1 Router(config-isis)# net 49.0001.0000.0000.0010.00 Router(config-isis)# nsr Router(config-isis)# nsf ietf Router(config-isis)# log adjacency changes Router(config-isis)# address-family ipv4 unicast Router(config-isis-af)# metric-style wide Router(config-isis-af)# exit Router(config-isis)# interface Bundle-Ether12 Router(config-isis-if)# point-to-point Router(config-isis-if)# address-family ipv4 unicast Router(config-isis-if-af)# exit Router(config-isis-if)# exit Router(config-isis)# interface Loopback0 Router(config-isis-if)# point-to-point Router(config-isis-if)# address-family ipv4 unicast Router(config-isis-if-af)# exit Router(config-isis-if)# exit Router(config-isis)# exit Router(config)# mpls ldp Router(config-ldp)# nsr Router(config-ldp)# interface Bundle-Ether12 Router(config-ldp-if)# exit Router(config-ldp)# exit Router(config)# router bgp 65000 Router(config-bgp)# nsr Router(config-bgp)# bgp router-id 10.10.10.10 Router(config-bgp)# bgp graceful-restart Router(config-bgp)# address-family vpnv4 unicast Router(config-bgp-af)# retain route-target all Router(config-bgp-af)# label mode per-nexthop-received-label Router(config-bgp-af)# exit Router(config-bgp)# address-family vpnv6 unicast Router(config-bgp-af)# label mode per-nexthop-received-label Router(config-bgp-af)# retain route-target all Router(config-bgp-af)# exit Router(config-bgp)# neighbor 10.0.0.1 Router(config-bgp-nbr)# remote-as 65001 Router(config-bgp-nbr)# ebgp-multihop 2 Router(config-bgp-nbr)# update-source Loopback0 Router(config-bgp-nbr)# address-family vpnv4 unicast Router(config-bgp-nbr-af)# route-policy pass-all in Router(config-bgp-nbr-af)# maximum-prefix 4500000 90 Router(config-bgp-nbr-af)# route-policy pass-all out Router(config-bgp-nbr-af)# exit Router(config-bgp-nbr)# address-family vpnv6 unicast Router(config-bgp-nbr-af)# route-policy pass-all in Router(config-bgp-nbr-af)# maximum-prefix 4500000 90 Router(config-bgp-nbr-af)# route-policy pass-all out Router(config-bgp-nbr-af)# exit Router(config-bgp-nbr)# exit Router(config-bgp)# neighbor 192.168.255.2 Router(config-bgp-nbr)# remote-as 65000 Router(config-bgp-nbr)# update-source Loopback0 Router(config-bgp-nbr)# address-family vpnv4 unicast Router(config-bgp-nbr-af)# maximum-prefix 4500000 90 Router(config-bgp-nbr-af)# next-hop-self Router(config-bgp-nbr-af)# exit Router(config-bgp-nbr)# address-family vpnv6 unicast Router(config-bgp-nbr-af)# maximum-prefix 4500000 90 Router(config-bgp-nbr-af)# next-hop-self Router(config-bgp-nbr-af)# exit Router(config-bgp-nbr)# exit Router(config-bgp)# exit Router(config)# router static Router(config-static)# address-family ipv4 unicast Router(config-static-afi)# 10.0.0.1/32 Bundle-Ether11 10.1.0.2 Router(config-static-afi)# commit
	4.	Configure ASBR2 for Inter-AS Option B. Example: Router# configure Router(config)# interface Loopback0 Router(config-if)# ipv4 address 10.0.0.1 255.255.255.255 Router(config-if)# ipv6 address 1:1:1::1/128 Router(config-if)# exit Router(config)# interface Bundle-Ether12 Router(config-if)# description interface to P2 Router(config-if)# ipv4 address 192.0.2.14 255.240.0.0 Router(config-if)# monitor-session Test ethernet port-level Router(config-if-mon)# exit Router(config-if)# exit Router(config)# interface Bundle-Ether11 Router(config-if)# description interface to ASBR1 Router(config-if)# ipv4 address 10.1.0.2 255.255.255.0 Router(config-if)# exit Router(config)# router isis core Router(config-isis)# is-type level-1 Router(config-isis)# net 49.0001.0000.0000.0010.00 Router(config-isis)# nsr Router(config-isis)# nsf ietf Router(config-isis)# log adjacency changes Router(config-isis)# address-family ipv4 unicast Router(config-isis-af)# metric-style wide Router(config-isis-af)# exit Router(config-isis)# interface Bundle-Ether12 Router(config-isis-if)# point-to-point Router(config-isis-if)# address-family ipv4 unicast Router(config-isis-if-af)# exit Router(config-isis-if)# exit Router(config-isis)# interface Loopback0 Router(config-isis-if)# point-to-point Router(config-isis-if)# address-family ipv4 unicast Router(config-isis-if-af)# exit Router(config-isis-if)# exit Router(config-isis)# exit Router(config)# mpls ldp Router(config-ldp)# nsr Router(config-ldp)# interface Bundle-Ether12 Router(config-ldp-if)# exit Router(config-ldp)# exit Router(config)# router bgp 65001 Router(config-bgp)# nsr Router(config-bgp)# bgp router-id 10.0.0.1 Router(config-bgp)# bgp graceful-restart Router(config-bgp)# address-family vpnv4 unicast Router(config-bgp-af)# label mode per-nexthop-received-label Router(config-bgp-af)# retain route-target all Router(config-bgp-af)# exit Router(config-bgp)# address-family vpnv6 unicast Router(config-bgp-af)# label mode per-nexthop-received-label Router(config-bgp-af)# retain route-target all Router(config-bgp-af)# exit Router(config-bgp)# neighbor 192.0.2.15 Router(config-bgp-nbr)# remote-as 65001 Router(config-bgp-nbr)# update-source Loopback0 Router(config-bgp-nbr)# address-family vpnv4 unicast Router(config-bgp-nbr-af)# next-hop-self Router(config-bgp-nbr-af)# exit Router(config-bgp-nbr)# address-family vpnv6 unicast Router(config-bgp-nbr-af)# next-hop-self Router(config-bgp-nbr-af)# exit Router(config-bgp-nbr)# exit Router(config-bgp)# neighbor 10.10.10.10 Router(config-bgp-nbr)# remote-as 65000 Router(config-bgp-nbr)# ebgp-multihop 2 Router(config-bgp-nbr)# update-source Loopback0 Router(config-bgp-nbr)# address-family vpnv4 unicast Router(config-bgp-nbr-af)# route-policy pass-all in Router(config-bgp-nbr-af)# maximum-prefix 4500000 90 Router(config-bgp-nbr-af)# route-policy pass-all out Router(config-bgp-nbr-af)# exit Router(config-bgp-nbr)# address-family vpnv6 unicast Router(config-bgp-nbr-af)# route-policy pass-all in Router(config-bgp-nbr-af)# maximum-prefix 4500000 90 Router(config-bgp-nbr-af)# route-policy pass-all out Router(config-bgp-nbr-af)# exit Router(config-bgp-nbr)# exit Router(config-bgp)# exit Router(config)# router static Router(config-static)# address-family ipv4 unicast Router(config-static-afi)# 10.10.10.10/32 Bundle-Ether11 10.1.0.1 Router(config-static-afi)# commit
	5.	Configure P2 for Inter-AS Option B. Example: Router# configure Router(config)# interface Loopback0 Router(config-if)# ipv4 address 192.0.2.2 255.255.255.255 Router(config-if)# exit Router(config)# interface Bundle-Ether12 Router(config-if)# description interface towards ASBR2 Router(config-if)# ipv4 address 192.0.2.16 255.240.0.0 Router(config-if)# exit Router(config)# interface Bundle-Ether25 Router(config-if)# description interface towards PE2 Router(config-if)# ipv4 address ipv4 address 192.0.2.17 255.240.0.0 Router(config-if)# exit Router(config)# router isis core Router(config-isis)# is-type level-1 Router(config-isis)# net 49.0001.0000.0000.0020.00 Router(config-isis)# nsr Router(config-isis)# nsf ietf Router(config-isis)# log adjacency changes Router(config-isis)# address-family ipv4 unicast Router(config-isis-af)# metric-style wide Router(config-isis-af)# exit Router(config-isis)# interface Bundle-Ether12 Router(config-isis-if)# point-to-point Router(config-isis-if)# address-family ipv4 unicast Router(config-isis-if-af)# exit Router(config-isis-if)# exit Router(config-isis)# interface Bundle-Ether25 Router(config-isis-if)# point-to-point Router(config-isis-if)# address-family ipv4 unicast Router(config-isis-if-af)# exit Router(config-isis-if)# exit Router(config-isis)# interface Loopback0 Router(config-isis-if)# point-to-point Router(config-isis-if)# address-family ipv4 unicast Router(config-isis-if-af)# exit Router(config-isis-if)# exit Router(config-isis-if)# exit Router(config-isis)# exit Router(config)# mpls ldp Router(config-ldp)# interface Bundle-Ether12 Router(config-ldp-if)# exit Router(config-ldp)# interface Bundle-Ether25 Router(config-ldp-if)# commit
	6.	Configure PE2 for Inter-AS Option B. Example: Router(config)# router bgp 65001 Router(config-bgp)# nsr Router(config-bgp)# bgp router-id 192.168.255.12 Router(config-bgp)# bgp graceful-restart Router(config-bgp)# address-family vpnv4 unicast Router(config-bgp-af)# exit Router(config-bgp)# address-family vpnv6 unicast Router(config-bgp-af)# exit Router(config-bgp)# neighbor 10.0.0.1 Router(config-bgp-nbr)# remote-as 65001 Router(config-bgp-nbr)# update-source Loopback0 Router(config-bgp-nbr)# address-family vpnv4 unicast Router(config-bgp-nbr-af)# maximum-prefix 4500000 90 Router(config-bgp-nbr-af)# exit Router(config-bgp-nbr)# address-family vpnv6 unicast Router(config-bgp-nbr-af)# maximum-prefix 4500000 90 Router(config-bgp-nbr-af)# exit Router(config-bgp-nbr)# exit Router(config-bgp)# vrf vrf1 Router(config-bgp-vrf)# rd 100:1 Router(config-bgp-vrf)# bgp router-id 192.168.255.12 Router(config-bgp-vrf)# address-family ipv4 unicast Router(config-bgp-vrf-af)# label mode per-vrf Router(config-bgp-vrf-af)# redistribute connected Router(config-bgp-vrf-af)# exit Router(config-bgp-vrf)# address-family ipv6 unicast Router(config-bgp-vrf-af)# label mode per-vrf Router(config-bgp-vrf-af)# redistribute connected Router(config-bgp-vrf-af)# exit Router(config-bgp-vrf)# neighbor 192.0.2.12 Router(config-bgp-vrf-nbr)# remote-as 501 Router(config-bgp-vrf-nbr)# address-family ipv4 unicast Router(config-bgp-vrf-nbr-af)# route-policy pass-all in Router(config-bgp-vrf-nbr-af)# route-policy pass-all out Router(config-bgp-vrf-nbr-af)# exit Router(config-bgp-vrf-nbr)# exit Router(config-bgp-vrf)# neighbor 150:1:1::2 Router(config-bgp-vrf-nbr)# remote-as 501 Router(config-bgp-vrf-nbr)# address-family ipv6 unicast Router(config-bgp-vrf-nbr-af)# route-policy pass-all in Router(config-bgp-vrf-nbr-af)# route-policy pass-all out Router(config-bgp-vrf-nbr-af)# exit Router(config-bgp-vrf-nbr)# exit Router(config-bgp-vrf)# exit Router(config-bgp)# exit Router(config-bgp)# exit Router(config)# interface TenGigE0/0/0/30.1 Router(config-subif)# vrf vrf1 Router(config-subif)# ipv4 address 172.16.0.1 255.240.0.0 Router(config-subif)# ipv6 address 105:1:1::1/96 Router(config-subif)# encapsulation dot1q 1 Router(config-subif)# exit Router(config)# interface Loopback0 Router(config-if)# ipv4 address 192.168.255.12 255.255.255.224 Router(config-if)# ipv6 address 50:50:50::50/128 Router(config-if)# exit Router(config)# router isis access Router(config-isis)# is-type level-1 Router(config-isis)# net 49.0001.0000.0000.0050.00 Router(config-isis)# nsr Router(config-isis)# nsf ietf Router(config-isis)# log adjacency changes Router(config-isis)# address-family ipv4 unicast Router(config-isis-af)# metric-style wide Router(config-isis-af)# exit Router(config-isis)# interface Bundle-Ether25 Router(config-isis-if)# point-to-point Router(config-isis-if)# address-family ipv4 unicast Router(config-isis-if-af)# exit Router(config-isis-if)# exit Router(config-isis)# interface Loopback0 Router(config-isis-if)# point-to-point Router(config-isis-if)# address-family ipv4 unicast Router(config-isis-if-af)# exit Router(config-isis-if)# exit Router(config-isis)# exit Router(config)# mpls ldp Router(config-ldp)# interface Bundle-Ether25 Router(config-ldp-if)# exit Router(config-ldp)# exit Router(config)# vrf vrf1 Router(config-vrf)# address-family ipv4 unicast Router(config-vrf-af)# import route-target 100:1 Router(config-vrf-af)# export route-target 100:1 Router(config-vrf-af)# exit Router(config-vrf)# address-family ipv6 unicast Router(config-vrf-af)# import route-target 100:1 Router(config-vrf-af)# export route-target 100:1 Router(config-vrf-af)# commit
	7.	Review the running configuration on all devices. Example: PE1 running configuration interface Loopback0 ipv4 address 192.168.255.2/32 ipv6 address 50:50:50::50/128 ! interface Bundle-Ether25 description interface to R4 ipv4 address 172.16.0.1 255.240.0.0 ! ! router isis access is-type level-1 net 49.0001.0000.0000.0050.00 nsr nsf ietf log adjacency changes address-family ipv4 unicast metric-style wide ! interface Bundle-Ether25 point-to-point address-family ipv4 unicast ! ! interface Loopback0 point-to-point address-family ipv4 unicast ! ! ! mpls ldp interface Bundle-Ether25 ! ! vrf vrf1 address-family ipv4 unicast import route-target 100:1 ! export route-target 100:1 ! ! address-family ipv6 unicast import route-target 100:1 ! export route-target 100:1 ! ! ! router bgp 65000 nsr bgp router-id 192.168.255.2 bgp graceful-restart address-family vpnv4 unicast ! address-family vpnv6 unicast ! neighbor 10.10.10.10 remote-as 65000 update-source Loopback0 address-family vpnv4 unicast maximum-prefix 4500000 90 ! address-family vpnv6 unicast maximum-prefix 4500000 90 ! ! vrf vrf1 rd 100:1 bgp router-id 192.168.255.2 address-family ipv4 unicast label mode per-vrf redistribute connected ! address-family ipv6 unicast label mode per-vrf redistribute connected ! neighbor 192.0.2.12 remote-as 501 address-family ipv4 unicast route-policy pass-all in route-policy pass-all out ! ! neighbor 150:1:1::2 remote-as 501 address-family ipv6 unicast route-policy pass-all in route-policy pass-all out ! ! ! P1 running configuration interface Loopback0 ipv4 address 172.16.0.1 255.255.255.255 ! interface Bundle-Ether12 description interface to ASBR1 ipv4 address 10.20.1.2 255.240.0.0 ! interface Bundle-Ether25 description interface to R50 ipv4 address 192.0.2.13 255.240.0.0 ! router isis core is-type level-1 net 49.0001.0000.0000.0020.00 nsr nsf ietf log adjacency changes address-family ipv4 unicast metric-style wide ! interface Bundle-Ether12 point-to-point address-family ipv4 unicast ! ! interface Bundle-Ether25 point-to-point address-family ipv4 unicast ! ! interface Loopback0 point-to-point address-family ipv4 unicast ! ! ! mpls ldp nsr interface Bundle-Ether12 ! interface Bundle-Ether25 ! ! ASBR1 running configuration interface Loopback0 ipv4 address 10.10.10.10 255.255.255.255 ipv6 address 10:10:10::10/128 ! interface Bundle-Ether12 description interface to 172.16.0.1 ipv4 address 10.20.1.1 255.240.0.0 monitor-session Test ethernet port-level ! ! interface Bundle-Ether11 description interface to ASBR2 ipv4 address 10.1.0.1 255.255.255.0 ! router isis core is-type level-1 net 49.0001.0000.0000.0010.00 nsr nsf ietf log adjacency changes address-family ipv4 unicast metric-style wide ! interface Bundle-Ether12 point-to-point address-family ipv4 unicast ! ! interface Loopback0 point-to-point address-family ipv4 unicast ! ! ! mpls ldp nsr interface Bundle-Ether12 ! ! router bgp 65000 nsr bgp router-id 10.10.10.10 bgp graceful-restart address-family vpnv4 unicast label mode per-nexthop-received-label retain route-target all ! address-family vpnv6 unicast label mode per-nexthop-received-label retain route-target all ! neighbor 10.0.0.1 remote-as 65001 ebgp-multihop 2 update-source Loopback0 address-family vpnv4 unicast route-policy pass-all in maximum-prefix 4500000 90 route-policy pass-all out ! address-family vpnv6 unicast route-policy pass-all in maximum-prefix 4500000 90 route-policy pass-all out ! ! neighbor 192.168.255.2 remote-as 65000 update-source Loopback0 address-family vpnv4 unicast maximum-prefix 4500000 90 next-hop-self ! address-family vpnv6 unicast maximum-prefix 4500000 90 next-hop-self ! ! ! router static address-family ipv4 unicast 10.0.0.1/32 Bundle-Ether11 10.1.0.2 ! ! ASBR2 running configuration interface Loopback0 ipv4 address 10.0.0.1 255.255.255.255 ipv6 address 1:1:1::1/128 ! interface Bundle-Ether12 description interface to P2 ipv4 address 192.0.2.14 255.240.0.0 ! interface Bundle-Ether11 description interface to ASBR1 ipv4 address 10.1.0.2 255.255.255.0 ! router isis core is-type level-1 net 49.0001.0000.0000.0001.00 nsr distribute link-state nsf ietf log adjacency changes address-family ipv4 unicast metric-style wide ! interface Bundle-Ether12 point-to-point address-family ipv4 unicast ! ! interface Loopback0 point-to-point address-family ipv4 unicast ! ! ! mpls ldp interface Bundle-Ether12 ! ! router bgp 65001 nsr bgp router-id 10.0.0.1 bgp graceful-restart address-family ipv4 unicast ! address-family vpnv4 unicast label mode per-nexthop-received-label retain route-target all ! address-family vpnv6 unicast label mode per-nexthop-received-label retain route-target all ! neighbor 192.0.2.15 remote-as 65001 update-source Loopback0 address-family vpnv4 unicast next-hop-self ! address-family vpnv6 unicast next-hop-self ! ! neighbor 10.10.10.10 remote-as 65000 ebgp-multihop 2 update-source Loopback0 address-family vpnv4 unicast route-policy pass-all in maximum-prefix 4500000 90 route-policy pass-all out ! address-family vpnv6 unicast route-policy pass-all in maximum-prefix 4500000 90 route-policy pass-all out ! ! router static address-family ipv4 unicast 10.10.10.10/32 Bundle-Ether11 10.1.0.1 ! P2 running configuration interface Loopback0 ipv4 address 192.0.2.2 255.255.255.255 ! interface Bundle-Ether12 description interface towards ASBR2 ipv4 address 192.0.2.16 255.240.0.0 ! interface Bundle-Ether25 description interface towards PE2 ipv4 address 192.0.2.17 255.240.0.0 ! router isis core is-type level-1 net 49.0001.0000.0000.0002.00 nsr nsf ietf log adjacency changes address-family ipv4 unicast metric-style wide ! interface Bundle-Ether12 point-to-point address-family ipv4 unicast ! ! interface Bundle-Ether25 point-to-point address-family ipv4 unicast ! ! interface Loopback0 point-to-point address-family ipv4 unicast ! ! ! mpls ldp interface Bundle-Ether12 ! interface Bundle-Ether25 ! ! PE2 running configuration router bgp 65001 nsr bgp router-id 192.168.255.12 bgp graceful-restart address-family vpnv4 unicast ! address-family vpnv6 unicast ! neighbor 10.0.0.1 remote-as 65001 update-source Loopback0 address-family vpnv4 unicast maximum-prefix 4500000 90 ! address-family vpnv6 unicast maximum-prefix 4500000 90 ! ! vrf vrf1 rd 100:1 bgp router-id 192.168.255.12 address-family ipv4 unicast label mode per-vrf redistribute connected ! address-family ipv6 unicast label mode per-vrf redistribute connected ! neighbor 192.0.2.11 remote-as 501 address-family ipv4 unicast route-policy pass-all in route-policy pass-all out ! ! neighbor 105:1:1::2 remote-as 501 address-family ipv6 unicast route-policy pass-all in route-policy pass-all out ! ! ! interface TenGigE0/0/0/30.1 vrf vrf1 ipv4 address 192.0.2.18 255.240.0.0 ipv6 address 105:1:1::1/96 encapsulation dot1q 1 ! interface Loopback0 ipv4 address 192.0.2.15 255.255.255.255 ipv6 address 5:5:5::5/128 ! router isis access is-type level-1 net 49.0001.0000.0000.0005.00 nsr nsf ietf log adjacency changes address-family ipv4 unicast metric-style wide ! interface Bundle-Ether25 point-to-point address-family ipv4 unicast ! ! interface Loopback0 point-to-point address-family ipv4 unicast ! ! ! mpls ldp interface Bundle-Ether25 ! ! vrf vrf1 address-family ipv4 unicast import route-target 100:1 ! export route-target 100:1 ! ! address-family ipv6 unicast import route-target 100:1 ! export route-target 100:1
	8.	Verify route, label, and forwarding state across the topology. Example: Verification on PE1. L3VPN route 192.0.2.10/24 is learned through iBGP from ASBR1 on PE1 over address family VPNv4 unicast. Router-PE1# show route vrf vrf1 Sun Jun 6 23:08:38.433 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 - IS-IS, 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, l - LISP A - access/subscriber, a - Application route M - mobile route, r - RPL, t - Traffic Engineering, (!) - FRR Backup path Gateway of last resort is not set B 192.0.2.19/24 [200/0] via 10.10.10.10 (nexthop in vrf default), 00:04:43 C 192.0.2.20/24 is directly connected, 01:14:27, TenGigE0/0/0/22/0.1 L 192.0.2.21/32 is directly connected, 01:14:27, TenGigE0/0/0/22/0.1 B 192.0.2.10/24 [200/0] via 10.10.10.10 (nexthop in vrf default), 00:00:08 B 192.0.2.22/24 [200/0] via 10.10.10.10 (nexthop in vrf default), 00:00:08 The following output shows that you can reach 192.0.2.10/24 using a VPN label of 24521. The next hop for the VPNv4 prefix decides the transport label as well as the label switched path. Router-PE1# show bgp vpnv4 unicast rd 100:1 192.0.2.10/24 Sun Jun 6 23:12:12.140 UTC BGP routing table entry for 192.0.2.10/24, Route Distinguisher: 100:1 Versions: Process bRIB/RIB SendTblVer Speaker 2844 2844 Last Modified: Jun 6 23:08:30.194 for 00:03:42 Paths: (1 available, best #1) Not advertised to any peer Path #1: Received by speaker 0 Not advertised to any peer 200 501 10.10.10.10 (metric 30) from 10.10.10.10 (10.10.10.10) Received Label 24521 Origin IGP, localpref 100, valid, internal, best, group-best, import-candidate, imported Received Path ID 0, Local Path ID 1, version 2844 Extended community: RT:100:1 Source AFI: VPNv4 Unicast, Source VRF: vrf1, Source Route Distinguisher: 100:1 Router-PE1# show cef vrf vrf1 192.0.2.10 Mon Jun 7 02:07:39.841 UTC 192.0.2.10/24, version 513583, internal 0x5000001 0x30 (ptr 0xa3f8bac8) [1], 0x0 (0x0), 0x208 (0x8f505928) Updated Jun 7 01:50:33.710 Prefix Len 24, traffic index 0, precedence n/a, priority 3 gateway array (0x8f2d20e8) reference count 252, flags 0x2038, source rib (7), 0 backups [1 type 1 flags 0x48441 (0x8ad86708) ext 0x0 (0x0)] LW-LDI[type=0, refc=0, ptr=0x0, sh-ldi=0x0] gateway array update type-time 1 Jun 6 23:20:45.951 LDI Update time Jun 6 23:20:45.951 via 10.10.10.10/32, 5 dependencies, recursive [flags 0x6000] path-idx 0 NHID 0x0 [0xa25ff9d8 0x0] recursion-via-/32 next hop VRF - 'default', table - 0xe0000000 next hop 10.10.10.10/32 via 24003/0/21 next hop 192.0.2.13/32 BE25 labels imposed {24004 24521} Load distribution: 0 (refcount 1) Hash OK Interface Address 0 Y recursive 24003/0 The following output shows the transport label information to reach 192.0.2.10/24. Router-PE1# show mpls forwarding prefix 10.10.10.10/32 Mon Jun 7 02:06:40.845 UTC Local Outgoing Prefix Outgoing Next Hop Bytes Label Label or ID Interface Switched ------ ----------- ------------------ ------------ --------------- ------------ 24003 24004 10.10.10.10/32 BE25 192.0.2.13 141107 ------------------------------------------------------------------------------- Router:PE1# show cef vrf vrf1 192.0.2.10 Mon Jun 7 02:07:39.841 UTC 192.0.2.10/24, version 513583, internal 0x5000001 0x30 (ptr 0xa3f8bac8) [1], 0x0 (0x0), 0x208 (0x8f505928) Updated Jun 7 01:50:33.710 Prefix Len 24, traffic index 0, precedence n/a, priority 3 gateway array (0x8f2d20e8) reference count 252, flags 0x2038, source rib (7), 0 backups [1 type 1 flags 0x48441 (0x8ad86708) ext 0x0 (0x0)] LW-LDI[type=0, refc=0, ptr=0x0, sh-ldi=0x0] gateway array update type-time 1 Jun 6 23:20:45.951 LDI Update time Jun 6 23:20:45.951 via 10.10.10.10/32, 5 dependencies, recursive [flags 0x6000] path-idx 0 NHID 0x0 [0xa25ff9d8 0x0] recursion-via-/32 next hop VRF - 'default', table - 0xe0000000 next hop 10.10.10.10/32 via 24003/0/21 next hop 192.0.2.13/32 BE25 labels imposed {24004 24521} Load distribution: 0 (refcount 1) Hash OK Interface Address 0 Y recursive 24003/0 Verification on P1. P1 performs a PHP operation for transport label and exposes the VPN label before forwarding the traffic to next-hop 10.10.10.10. `Router-P1# show mpls forwarding prefix 10.10.10.10/32 Mon Jun 7 02:34:55.293 UTC Local Outgoing Prefix Outgoing Next Hop Bytes Label Label or ID Interface Switched ------ ----------- ------------------ ------------ --------------- ------------ 24004 Pop 10.10.10.10/32 BE12 10.20.1.1 28804 -------------------------------------------------------------------------------` Verification on ASBR1. ASBR1 learns the remote route 192.0.2.10/24 from ASBR2 through address-family VPNv4 unicast. The next hop is the ASBR2 loopback0. After receiving this update, it is advertised to the local PE1 through iBGP address-family VPNv4 unicast. The next-hop-self configuration is used on ASBR1 since it is reachable through IGP from PE1, so the next hop is changed to itself. The traffic arrives from PE1 with a label 24521 and is swapped with label 25516 before forwarding it to ASBR2. Router-ASBR1# show bgp vpnv4 unicast rd 100:1 192.0.2.10 Sun Jun 6 19:28:09.018 EDT BGP routing table entry for 192.0.2.10/24, Route Distinguisher: 100:1 Versions: Process bRIB/RIB SendTblVer Speaker 1002022 1002022 Local Label: 24521 Paths: (1 available, best #1) Advertised to update-groups (with more than one peer): 0.3 Path #1: Received by speaker 0 Advertised to update-groups (with more than one peer): 0.3 200 501 10.0.0.1 from 10.0.0.1 (10.0.0.1) Received Label 25516 Origin IGP, localpref 100, valid, external, best, group-best, import-candidate, not-in-vrf Received Path ID 0, Local Path ID 1, version 1002022 Extended community: RT:100:1 Router-ASBR1# show bgp vpnv4 unicast rd 100:1 advertised neighbor 192.168.255.2 summary Network Next Hop From AS Path Route Distinguisher: 100:1 192.0.2.19/24 10.10.10.10 10.0.0.1 200? 192.0.2.10/24 10.10.10.10 10.0.0.1 200 501i 192.0.2.22/24 10.10.10.10 10.0.0.1 200 501i Processed 3 prefixes, 3 paths Router-ASBR1# show mpls forwarding labels 24521 Sun Jun 6 23:05:49.323 EDT Local Outgoing Prefix Outgoing Next Hop Bytes Label Label or ID Interface Switched ------ ----------- ------------------ ------------ --------------- ------------ 24521 25516 100:1:192.0.2.10/24 10.1.0.1 0 ------------------------------------------------------------------------------- Verification on ASBR2. The prefix 192.0.2.10/24 is received through iBGP address-family VPNv4 unicast from PE2 with a label of 24002. ASBR2 assigns it a local label of 25516 and advertises it to ASBR1 through eBGP vpnv4 address-family changing the next hop to itself. This local label of 25516 is used by the ASBR1 to forward traffic to ASBR2, which in turn swaps it with a VPN label of 24002 before forwarding it to the next hop. Router-ASBR2# show bgp vpnv4 unicast rd 100:1 192.0.2.10 Sun Jun 6 23:06:32.812 EDT BGP routing table entry for 192.0.2.10/24, Route Distinguisher: 100:1 Versions: Process bRIB/RIB SendTblVer Speaker 16194881 16194881 Local Label: 25516 Gateway Array ID: 21940, Resilient per-PE nexthop set ID: 19598 Paths: (1 available, best #1) Advertised to update-groups (with more than one peer): 0.3 Path #1: Received by speaker 0 Advertised to update-groups (with more than one peer): 0.3 501 192.0.2.15 (metric 30) from 192.0.2.15 (192.0.2.15) Received Label 24002 Origin IGP, localpref 100, valid, internal, best, group-best, import-candidate, not-in-vrf Received Path ID 0, Local Path ID 1, version 16194881 Extended community: RT:100:1 Router-ASBR2# show bgp vpnv4 unicast rd 100:1 advertised neighbor 10.10.10.10 summary Sun Jun 6 23:07:05.617 EDT Network Next Hop From AS Path Route Distinguisher: 100:1 192.0.2.19/24 10.0.0.1 192.0.2.15 200? 192.0.2.20/24 10.0.0.1 10.10.10.10 200 100? 192.0.2.10/24 10.0.0.1 192.0.2.15 200 501i 192.0.2.22/24 10.0.0.1 192.0.2.15 200 501i Processed 4 prefixes, 4 paths Router-ASBR2# show mpls forwarding labels 25516 Sun Jun 6 23:07:32.394 EDT Local Outgoing Prefix Outgoing Next Hop Bytes Label Label or ID Interface Switched ------ ----------- ------------------ ------------ --------------- ------------ 25516 24002 No ID 192.0.2.15 654 ------------------------------------------------------------------------------- Verification on P2. P2 is along the transit path of the traffic. It label switches or pops the transport label. In this example, PHP operation is performed and exposes the VPN label before forwarding the traffic. Router-P2# show mpls forwarding prefix 192.0.2.15/32 Mon Jun 7 03:09:11.532 UTC Local Outgoing Prefix Outgoing Next Hop Bytes Label Label or ID Interface Switched ------ ----------- ------------------ ------------ --------------- ------------ 24005 Pop 192.0.2.15/32 BE25 192.0.2.23 11921958 ------------------------------------------------------------------------------- Verification on PE2. L3VPN route 192.0.2.10/24 is learned from eBGP neighbor 192.0.2.11 (CE2 interface towards PE2) in vrf1. Router-PE2# show route vrf vrf1 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 - IS-IS, 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, l - LISP A - access/subscriber, a - Application route M - mobile route, r - RPL, t - Traffic Engineering, (!) - FRR Backup path Gateway of last resort is not set C 192.0.2.19/24 is directly connected, 6w4d, TenGigE0/0/0/30.1 L 192.0.2.18/32 is directly connected, 6w4d, TenGigE0/0/0/30.1 B 192.0.2.20/24 [200/0] via 10.0.0.1 (nexthop in vrf default), 03:58:16 B 192.0.2.24/24 [200/0] via 10.0.0.1 (nexthop in vrf default), 04:30:07 B 192.0.2.10/24 [20/0] via 192.0.2.11, 01:30:05 B 192.0.2.22/24 [20/0] via 192.0.2.11, 01:30:05 The route 192.0.2.10/24 gets installed in VRF1 with a local label of 24002 and then advertised through iBGP address-family VPNv4 unicast to ASBR2 changing the next hop to itself. ASBR2 adds this VPN label before forwarding it to PE2. Router-PE2# show bgp vpnv4 unicast rd 100:1 192.0.2.10 BGP routing table entry for 192.0.2.10/24, Route Distinguisher: 100:1 Versions: Process bRIB/RIB SendTblVer Speaker 1070062 1070062 Local Label: 24002 Last Modified: Jun 7 01:30:56.657 for 01:31:29 Paths: (1 available, best #1) Advertised to peers (in unique update groups): 10.0.0.1 Path #1: Received by speaker 0 Advertised to peers (in unique update groups): 10.0.0.1 501 192.0.2.11 from 192.0.2.11 (192.0.2.25) Origin IGP, localpref 100, valid, external, best, group-best, import-candidate Received Path ID 0, Local Path ID 1, version 1070062 Extended community: RT:100:1 The traffic that arrives from PE2 with a VPN label of 24002 is assigned an outgoing label aggregate, which means that the lookup is to be performed in vrf1 RIB to forward it to the next hop on 192.0.2.12. Router-PE2# show mpls forwarding labels 24002 Mon Jun 7 03:02:53.255 UTC Local Outgoing Prefix Outgoing Next Hop Bytes Label Label or ID Interface Switched ------ ----------- ------------------ ------------ --------------- ------------ 24002 Aggregate vrf1: Per-VRF Aggr[V] \ vrf1 138 ------------------------------------------------------------------------------- Router-PE2# show cef vrf vrf1 192.0.2.10 Mon Jun 7 03:04:08.268 UTC 192.0.2.10/24, version 3477, internal 0x1000001 0x30 (ptr 0x97f75328) [1], 0x0 (0x0), 0x0 (0x0) Updated Jun 7 01:30:57.120 Prefix Len 24, traffic index 0, precedence n/a, priority 3 gateway array (0x8c820f38) reference count 2, flags 0x2010, source rib (7), 0 backups [1 type 3 flags 0x48441 (0x8a79cd88) ext 0x0 (0x0)] LW-LDI[type=0, refc=0, ptr=0x0, sh-ldi=0x0] gateway array update type-time 1 Jun 7 01:30:57.120 LDI Update time Jun 7 01:30:57.120 Level 1 - Load distribution: 0 [0] via 192.0.2.11/32, recursive via 192.0.2.11/32, 3 dependencies, recursive, bgp-ext [flags 0x6020] path-idx 0 NHID 0x0 [0x8d575b80 0x0] next hop 192.0.2.11/32 via 192.0.2.11/32 Load distribution: 0 (refcount 1) Hash OK Interface Address 0 Y TenGigE0/0/0/30.1 192.0.2.11

Inter-AS Option B for L3VPN is configured and verified when routing, label, and forwarding tables display correct states and expected label mappings across all PE, P, and ASBR devices.

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