Case Study—Multi-Homed Inter-AS Provider Network

Figure 7-38 shows an Inter-AS network topology in which Service Provider 1 and Service Provider 2 are providing MPLS VPN services to geographically dispersed Customer A and B sites.

Figure 7-38. Multi-Homed Inter-AS Provider Network

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The provider network uses the RR method to reduce iBGP mesh. P1-AS1-RR and P1-AS2-RR serve as both an ASBR and a RR in the provider network. In this case study, ASBR1-AS1 and ASBR2-AS2 in the provider network use the Inter-AS redistribute connected option to distribute the next hop to devices in Provider Network 1, while P1-AS1-RR and P1-AS2-RR use the Inter-AS next-hop-self method to distribute next-hop information to devices in Provider Network 2. Provider 2, in this case study, also wants to ensure that Customer A traffic uses the Inter-AS Link A and Customer B traffic uses the Inter-AS Link B, and, in case any link goes down, both customers’ traffic should be routed across the other operational link. Example 7-31 shows the ASBR and PE router configuration. Refer to Example 7-3 and Example 7-4 for CE configurations.

Example 7-31. Multi-Homed Inter-AS Provider Network Router Configurations
hostname ASBR2-AS1
					!
					ip cef
					!
					mpls ldp router-id Loopback0
					!
					interface Loopback0
					ip address 10.10.10.102 255.255.255.255
					!
					interface Ethernet0/0
					ip address 10.10.10.5 255.255.255.252
					mpls ip
					!
					interface Ethernet1/0
					ip address 10.10.10.10 255.255.255.252
					mpls ip
					!
					interface Serial2/0
					ip address 10.40.40.1 255.255.255.252
					mpls bgp forwarding
					!
					router ospf 1
					redistribute connected subnets route-map adv-conn
					network 10.10.10.0 0.0.0.255 area 0
					!
					router bgp 1
					no bgp default ipv4-unicast
					no bgp default route-target filter
					neighbor 10.10.10.100 remote-as 1
					neighbor 10.10.10.100 update-source Loopback0
					neighbor 10.40.40.2 remote-as 2
					!
					address-family vpnv4
					neighbor 10.10.10.100 activate
					neighbor 10.10.10.100 send-community extended
					neighbor 10.40.40.2 activate
					neighbor 10.40.40.2 send-community extended
					exit-address-family
					!
					access-list 1 permit 172.16.10.0
					access-list 2 permit 192.168.10.0
					access-list 10 permit 10.40.40.2
					!
					route-map adv-conn permit 10
					match ip address 10
__________________________________________________________________________
hostname ASBR2-AS2
					!
					ip cef
					!
					mpls ldp router-id Loopback0
					!
					interface Loopback0
					ip address 10.20.20.102 255.255.255.255
					!
					interface Ethernet0/0
					ip address 10.20.20.5 255.255.255.252
					mpls ip
					!
					interface Ethernet1/0
					ip address 10.20.20.10 255.255.255.252
					mpls ip
					!
					interface Serial2/0
					ip address 10.40.40.2 255.255.255.252
					mpls bgp forwarding
					!
					router ospf 2
					network 10.20.20.0 0.0.0.255 area 0
					!
					router bgp 2
					no synchronization
					no bgp default route-target filter
					neighbor 10.20.20.100 remote-as 2
					neighbor 10.20.20.100 update-source Loopback0
					neighbor 10.40.40.1 remote-as 1
					no auto-summary
					!
					address-family vpnv4
					neighbor 10.20.20.100 activate
					neighbor 10.20.20.100 send-community extended
					neighbor 10.20.20.100 next-hop-self
					neighbor 10.40.40.1 activate
					neighbor 10.40.40.1 send-community extended
					neighbor 10.40.40.1 route-map pref_192 in
					neighbor 10.40.40.1 route-map pref_192_local out
					exit-address-family
					!
					access-list 1 permit 192.168.10.0
					access-list 2 permit 172.16.10.0
					access-list 3 permit 192.168.20.0
					access-list 4 permit 172.16.20.0
					!
					route-map pref_192_local permit 10
					match ip address 3
					!
					route-map pref_192_local permit 20
					match ip address 4
					set as-path prepend 65501 65501 65501
					!
					route-map pref_192 permit 10
					match ip address 1
					set metric 50
					!
					route-map pref_192 permit 20
					match ip address 2
					set metric 100
__________________________________________________________________________
hostname PE1-AS1
					!
					ip cef
					!
					ip vrf Cust_A
					rd 1:100
					route-target export 1:100
					route-target import 2:100
					!
					ip vrf Cust_B
					rd 1:101
					route-target export 1:101
					route-target import 2:101
					!
					mpls ldp router-id Loopback0
					!
					interface Loopback0
					ip address 10.10.10.101 255.255.255.255
					!
					interface Ethernet0/0
					ip address 10.10.10.1 255.255.255.252
					mpls ip
					!
					interface Ethernet1/0
					ip address 10.10.10.9 255.255.255.252
					mpls ip
					!
					interface Serial2/0
					description connected to Cust_A CE1-A
					ip vrf forwarding Cust_A
					ip address 172.16.1.1 255.255.255.252
					!
					interface Serial3/0
					description connected to Cust_B CE1-B
					ip vrf forwarding Cust_B
					ip address 192.168.1.1 255.255.255.252
					!
					router ospf 1
					network 10.10.10.0 0.0.0.255 area 0
					!
					router bgp 1
					no bgp default ipv4-unicast
					neighbor 10.10.10.100 remote-as 1
					neighbor 10.10.10.100 update-source Loopback0
					!
					address-family vpnv4
					neighbor 10.10.10.100 activate
					neighbor 10.10.10.100 send-community extended
					exit-address-family
					!
					address-family ipv4 vrf Cust_B
					neighbor 192.168.1.2 remote-as 65001
					neighbor 192.168.1.2 activate
					neighbor 192.168.1.2 as-override
					no auto-summary
					no synchronization
					exit-address-family
					!
					address-family ipv4 vrf Cust_A
					neighbor 172.16.1.2 remote-as 65001
					neighbor 172.16.1.2 activate
					no auto-summary
					no synchronization
					exit-address-family
__________________________________________________________________________
hostname PE1-AS2
					!
					ip cef
					!
					ip vrf Cust_A
					rd 2:100
					route-target export 2:100
					route-target import 1:100
					!
					ip vrf Cust_B
					rd 2:101
					route-target export 2:101
					route-target import 1:101
					!
					mpls ldp router-id Loopback0
					!
					interface Loopback0
					ip address 10.20.20.101 255.255.255.255
					!
					interface Ethernet0/0
					ip address 10.20.20.1 255.255.255.252
					mpls ip
					!
					interface Ethernet1/0
					ip address 10.20.20.9 255.255.255.252
					mpls ip
					!
					interface Serial2/0
					description coonected to Cust_A CE2-A
					ip vrf forwarding Cust_A
					ip address 172.16.2.1 255.255.255.252
					!
					interface Serial3/0
					description coonected to Cust_B CE2-B
					ip vrf forwarding Cust_B
					ip address 192.168.2.1 255.255.255.252
					!
					router ospf 2
					network 10.20.20.0 0.0.0.255 area 0
					!
					router bgp 2
					no bgp default ipv4-unicast
					neighbor 10.20.20.100 remote-as 2
					neighbor 10.20.20.100 update-source Loopback0
					!
					address-family vpnv4
					neighbor 10.20.20.100 activate
					neighbor 10.20.20.100 send-community extended
					exit-address-family
					!
					address-family ipv4 vrf Cust_B
					neighbor 192.168.2.2 remote-as 65001
					neighbor 192.168.2.2 activate
					neighbor 192.168.2.2 as-override
					no auto-summary
					no synchronization
					exit-address-family
					!
					address-family ipv4 vrf Cust_A
					neighbor 172.16.2.2 remote-as 65002
					neighbor 172.16.2.2 activate
					no auto-summary
					no synchronization
					exit-address-family
__________________________________________________________________________
hostname ASBR1-AS1-RR
					!
					ip cef
					!
					mpls ldp router-id Loopback0
					!
					interface Loopback0
					ip address 10.10.10.100 255.255.255.255
					!
					interface Ethernet0/0
					ip address 10.10.10.2 255.255.255.252
					mpls ip
					!
					interface Ethernet1/0
					ip address 10.10.10.6 255.255.255.252
					mpls ip
					!
					interface Serial2/0
					ip address 10.30.30.1 255.255.255.252
					mpls bgp forwarding
					!
					router ospf 1
					redistribute connected subnets route-map adv-conn
					network 10.10.10.0 0.0.0.255 area 0
					!
					router bgp 1
					no bgp default ipv4-unicast
					no bgp default route-target filter
					neighbor 10.10.10.101 remote-as 1
					neighbor 10.10.10.101 update-source Loopback0
					neighbor 10.10.10.102 remote-as 1
					neighbor 10.30.30.2 remote-as 2
					!
					address-family vpnv4
					neighbor 10.10.10.101 activate
					neighbor 10.10.10.101 send-community extended
					neighbor 10.10.10.101 route-reflector-client
					neighbor 10.10.10.102 activate
					neighbor 10.10.10.102 send-community extended
					neighbor 10.10.10.102 route-reflector-client
					neighbor 10.30.30.2 activate
					neighbor 10.30.30.2 send-community extended
					exit-address-family
					!
					access-list 10 permit 10.30.30.2
					!
					route-map adv-conn permit 10
					match ip address 10
__________________________________________________________________________
hostname ASBR1-AS2-RR
					!
					ip cef
					!
					mpls ldp router-id Loopback0
					!
					interface Loopback0
					ip address 10.20.20.100 255.255.255.255
					!
					interface Ethernet0/0
					ip address 10.20.20.2 255.255.255.252
					mpls ip
					!
					interface Ethernet1/0
					ip address 10.20.20.6 255.255.255.252
					mpls ip
					!
					interface Serial2/0
					ip address 10.30.30.2 255.255.255.252
					mpls bgp forwarding
					!
					router ospf 2
					network 10.20.20.0 0.0.0.255 area 0
					!
					router bgp 2
					no synchronization
					no bgp default route-target filter
					neighbor 10.20.20.101 remote-as 2
					neighbor 10.20.20.101 update-source Loopback0
					neighbor 10.20.20.102 remote-as 2
					neighbor 10.20.20.102 update-source Loopback0
					neighbor 10.30.30.1 remote-as 1
					no auto-summary
					!
					address-family vpnv4
					neighbor 10.20.20.101 activate
					neighbor 10.20.20.101 send-community extended
					neighbor 10.20.20.101 route-reflector-client
					neighbor 10.20.20.101 next-hop-self
					neighbor 10.20.20.102 activate
					neighbor 10.20.20.102 send-community extended
					neighbor 10.20.20.102 route-reflector-client
					neighbor 10.20.20.102 next-hop-self
					neighbor 10.30.30.1 activate
					neighbor 10.30.30.1 send-community extended
					neighbor 10.30.30.1 route-map pref_172 in
					neighbor 10.30.30.1 route-map pref_172_local out
					exit-address-family
					!
					access-list 1 permit 172.16.10.0
					access-list 2 permit 192.168.10.0
					access-list 3 permit 172.16.20.0
					access-list 4 permit 192.168.20.0
					!
					route-map pref_172_local permit 10
					match ip address 3
					!
					route-map pref_172_local permit 20
					match ip address 4
					set as-path prepend 65501 65501 65501
					!
					route-map pref_172 permit 10
					match ip address 1
					set metric 50
					!
					route-map pref_172 permit 20
					match ip address 2
					set metric 100

Example 7-32 shows that, on PE1-AS1, 172.16.20.0/24 is reachable via Inter-AS Link A, and 192.168.20.0/24 is reachable via Inter-AS Link B. Based on the output shown in Example 7-32, traffic between Customer A sites take Inter-AS Link A and traffic between Customer B sites take Inter-AS Link B.

Example 7-32. Verifying End-to-End Connectivity
PE1-AS1#show ip bgp vpnv4 all
<truncated>
*>i172.16.20.0/24  10.30.30.2          0   100      0 2 65002 i
*>i192.168.20.0    10.40.40.2          0   100      0 2 65001 i
__________________________________________________________________________
PE1-AS2#show ip bgp vpnv4 all
<truncated>
*>i172.16.10.0/24  10.20.20.100       50   100      0 1 65001 i
*>i192.168.10.0    10.20.20.102       50   100      0 1 65001 i

Example 7-33 shows the result of the ping operation.

Example 7-33. Verify End-to-End Connectivity
CE1-A#ping 172.16.20.1 source 172.16.10.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.20.1, timeout is 2 seconds:
Packet sent with a source address of 172.16.10.1
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 60/60/60 ms
__________________________________________________________________________
CE1-B#ping 192.168.20.1 source 192.168.10.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.20.1, timeout is 2 seconds:
Packet sent with a source address of 192.168.10.1
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 60/60/60 ms

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