Inter-AS Option C

Scenario
This comparison shows an MPLS Inter-AS Option C setup as follows:

This setup shows both the ASBRs and the Route Reflectors with the following conditions:

• An eBGP VPNv4 multi-hop session is configured between the route-reflectors.
• An eBGP IPv4 session, with labels, is configured between the ASBRs.
• The loopback from the opposing AS are redistributed into the local OSPF IGP.
• Templates and Neighbor groups are used on the route-reflector.
• MPLS LDP autoconfig and LDP IGP Sync are used.
• Only host routes have labels assigned for the IGP and a label range has been configured.

For more information on how Inter-AS options work, including Option C, see this document.

IOS Config – ASBR

hostname ASBR1
!
mpls label range 1000 1999
mpls ldp label
 allocate global host-routes
!
!
interface Loopback0
 ip address 1.1.1.1 255.255.255.255
 ip ospf 1 area 0
!
interface GigabitEthernet1.122
 encapsulation dot1Q 122
 ip address 10.1.22.1 255.255.255.0
 mpls bgp forwarding
!
router ospf 1
 router-id 1.1.1.1
 log-adjacency-changes detail
 redistribute bgp 100 subnets
 passive-interface Loopback0
 mpls ldp sync
 mpls ldp autoconfig
!
router bgp 100
 bgp router-id 1.1.1.1
 bgp log-neighbor-changes
 no bgp default ipv4-unicast
 neighbor 5.5.5.5 remote-as 100
 neighbor 5.5.5.5 update-source Loopback0
 neighbor 10.1.22.22 remote-as 200
 !
 address-family ipv4
  network 1.1.1.1 mask 255.255.255.255
  network 2.2.2.2 mask 255.255.255.255
  network 3.3.3.3 mask 255.255.255.255
  network 5.5.5.5 mask 255.255.255.255
  neighbor 10.1.22.22 activate
  neighbor 10.1.22.22 route-map MATCH_LOOPBACKS out
  neighbor 10.1.22.22 send-label
 exit-address-family
 !
 address-family vpnv4
  neighbor 5.5.5.5 activate
  neighbor 5.5.5.5 send-community extended
  neighbor 5.5.5.5 next-hop-self
 exit-address-family
!
!
ip prefix-list MATCH_LOOPBACKS seq 5 permit 1.1.1.1/32
ip prefix-list MATCH_LOOPBACKS seq 10 permit 2.2.2.2/32
ip prefix-list MATCH_LOOPBACKS seq 15 permit 3.3.3.3/32
ip prefix-list MATCH_LOOPBACKS seq 20 permit 5.5.5.5/32
!
route-map MATCH_LOOPBACKS permit 10
 match ip address prefix-list MATCH_LOOPBACKS
 set mpls-label
!
mpls ldp router-id Loopback0
!

IOS Config – Route Reflector

hostname RR1
!
router bgp 100
 bgp router-id 5.5.5.5
 template peer-policy IBGP_PEER
  route-reflector-client
 exit-peer-policy
 !
 template peer-session IBGP_PEER
  remote-as 100
  update-source Loopback0
 exit-peer-session
 !
 bgp log-neighbor-changes
 neighbor 1.1.1.1 inherit peer-session IBGP_PEER
 neighbor 2.2.2.2 inherit peer-session IBGP_PEER
 neighbor 20.20.20.20 remote-as 200
 neighbor 20.20.20.20 ebgp-multihop 255
 neighbor 20.20.20.20 update-source Loopback0
 !
 address-family vpnv4
  neighbor 1.1.1.1 activate
  neighbor 1.1.1.1 send-community extended
  neighbor 1.1.1.1 inherit peer-policy IBGP_PEER
  neighbor 2.2.2.2 activate
  neighbor 2.2.2.2 send-community extended
  neighbor 2.2.2.2 inherit peer-policy IBGP_PEER
  neighbor 20.20.20.20 activate
  neighbor 20.20.20.20 send-community extended
  neighbor 20.20.20.20 next-hop-unchanged
 exit-address-family
!

XR Config – ASBR

hostname ASBR1
!
interface Loopback0
 ipv4 address 1.1.1.1 255.255.255.255
!
interface GigabitEthernet0/0/0/0.122
 ipv4 address 10.1.22.1 255.255.255.0
 encapsulation dot1q 122
!
prefix-set LOOPBACKS
  1.1.1.1,
  2.2.2.2,
  3.3.3.3,
  5.5.5.5
end-set
!
route-policy FROM_REMOTE_AS
  pass
end-policy
!
route-policy MATCH_LOOPBACKS
  if destination in LOOPBACKS then
    pass
  else
    drop
  endif
end-policy
!
! XR devices cannot label switch to a next-hop
! that is not learned via a /32 host. Hence the
! need for a static route here.
router static
 address-family ipv4 unicast
  10.1.22.22/32 GigabitEthernet0/0/0/0.122
 !
!
router ospf 1
 log adjacency changes detail
 router-id 1.1.1.1
 redistribute bgp 100
 area 0
  mpls ldp sync
  mpls ldp auto-config
  interface Loopback0
   passive enable
  !
  interface GigabitEthernet0/0/0/0.13
  !
 !
router bgp 100
 bgp router-id 1.1.1.1
 address-family ipv4 unicast
  network 1.1.1.1/32
  network 2.2.2.2/32
  network 3.3.3.3/32
  network 5.5.5.5/32
  allocate-label all
 !
 address-family vpnv4 unicast
 !
 neighbor 10.1.22.22
  remote-as 200
  address-family ipv4 labeled-unicast
   route-policy FROM_REMOTE_AS in
   route-policy MATCH_LOOPBACKS out
  !
 !
 neighbor 5.5.5.5
  remote-as 100
  update-source Loopback0
  address-family vpnv4 unicast
   next-hop-self
  !
 !
!
mpls ldp
 router-id 1.1.1.1
 address-family ipv4
  label
   local
    allocate for host-routes
   !
  !
 !
!
mpls label range table 0 16000 16999
!

XR Config – Router Reflector

hostname RR1
!
router bgp 100
 bgp router-id 5.5.5.5
 address-family vpnv4 unicast
 !
 neighbor-group IBGP_PEERS
  remote-as 100
  update-source Loopback0
  address-family vpnv4 unicast
   route-reflector-client
  !
 !
 neighbor 20.20.20.20
  remote-as 200
  ebgp-multihop 255
  update-source Loopback0
  address-family vpnv4 unicast
   route-policy PASS in
   route-policy PASS out
   next-hop-unchanged
  !
 !
 neighbor 1.1.1.1
  use neighbor-group IBGP_PEERS
  address-family vpnv4 unicast
  !
 !
 neighbor 2.2.2.2
  use neighbor-group IBGP_PEERS
  address-family vpnv4 unicast
  !
 !
!

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