Exploring the quirks of Network Engineering
Scenario
This comparison shows how Carrier Supporting Carrier is configured from the point of view of BB-PE2, an edge router for the backbone provider. OSPF + LDP is the internal configuration for the Backbone Provider. BGP-LU is configured between BB-PE2 and ASBR2.
This is best viewed alongside this CsC cheatsheet or one of these downloadable labs.
There is an alternate approach to CsC, using IGP+LDP between the Backbone Provider and the Customer Provider Edge Routers, but IOS-XR does not support VRF aware LDP. This means that in such as setup, an IOS-XR cannot play the role of the Backbone Edge Router.
IOS Config
hostname BB-PE2
!
ip cef
!
ip vrf CSC_CUST_ISP1
rd 100:500
route-target export 100:500
route-target import 100:500
!
!
!
interface Loopback0
ip address 100.2.2.2 255.255.255.255
ip ospf 1 area 0
!
interface GigabitEthernet0/1
description link to ASBR2
ip vrf forwarding CSC_CUST_ISP1
ip address 192.168.117.6 255.255.255.252
!
interface GigabitEthernet0/0
description link to BB-Core
ip address 10.30.23.2 255.255.255.0
ip ospf 1 area 0
!
router ospf 1
mpls ldp autoconfig
router-id 100.2.2.2
log-adjacency-changes
passive-interface Loopback0
!
router bgp 100
bgp router-id 100.2.2.2
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 100.1.1.1 remote-as 100
neighbor 100.1.1.1 update-source Loopback0
!
address-family vpnv4
neighbor 100.1.1.1 activate
neighbor 100.1.1.1 send-community extended
neighbor 100.1.1.1 next-hop-self
exit-address-family
!
address-family ipv4 vrf CSC_CUST_ISP1
neighbor 192.168.117.5 remote-as 500
neighbor 192.168.117.5 activate
neighbor 192.168.117.5 send-label
no synchronization
exit-address-family
!
XR Config
hostname BB-PE2
!
vrf CSC_CUST_ISP1
address-family ipv4 unicast
import route-target
100:500
!
export route-target
100:500
!
!
!
interface Loopback0
ipv4 address 100.2.2.2 255.255.255.255
!
interface GigabitEthernet0/0/0/1
description link to ASBR2
vrf CSC_CUST_ISP1
ipv4 address 192.168.117.6 255.255.255.252
!
interface GigabitEthernet0/0/0/0
description link to BB-Core
ipv4 address 10.30.23.2 255.255.255.0
!
route-policy PASS
pass
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
vrf CSC_CUST_ISP1
address-family ipv4 unicast
192.168.117.5/32 GigabitEthernet0/0/0/1
!
!
!
router ospf 1
log adjacency changes
address-family ipv4 unicast
area 0
mpls ldp auto-config
interface Loopback0
passive enable
!
interface GigabitEthernet0/0/0/0
!
!
!
router bgp 100
bgp router-id 100.2.2.2
bgp log neighbor changes detail
address-family vpnv4 unicast
!
neighbor 100.1.1.1
remote-as 100
update-source Loopback0
address-family vpnv4 unicast
next-hop-self
!
!
vrf CSC_CUST_ISP1
rd 100:500
! Note the need to specify allocate-label all on XR under
! the bgp vrf config
address-family ipv4 unicast
allocate-label all
!
neighbor 192.168.117.5
remote-as 500
address-family ipv4 labeled-unicast
route-policy PASS in
route-policy PASS out
!
!
!
!
! Remember to enable LDP globally
mpls ldp
address-family ipv4
!
!
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