Option 3: Multi-Hop MP-eBGP Between RR and eBGP Between ASBRs

This approach is considered to be more scalable than option 1 or option 2. In this option, VPNv4 information is held by the RRs. To meet this requirement, each provider needs to have local RRs for VPNv4 prefix distribution and eBGP connection to exchange prefixes with the external peer. The ASBRs in this option participate in exchange of BGP next-hop-address using IPv4 labels, and RRs form an MP-eBGP session to transport VPNv4 information. Figure 7-25 shows a multiprovider VPN network that is providing VPN services to sites belonging to Customer A.

Figure 7-25. MPLS VPN Network Using Option 3

[View full size image]

P1-AS1-RR and P1-AS2-RR are RRs that are local to each of the provider's autonomous systems. An MP-eBGP session is formed between the RRs to transport VPNv4 information across the multiprovider network. An eBGP session is formed between the ASBRs to exchange next-hop-address prefixes.

Control Plane Forwarding in Option 3

Figure 7-26 shows the control plane forwarding action that takes place for prefix 172.16.10.0/24 advertised by CE1-A to CE2-A that belongs to the same VPN, CUST_A.

Figure 7-26. Control Plane Operation in Option 3

[View full size image]

Data Forwarding in Option 3

The source and destination networks are located on two different MPLS VPN provider networks. The data forwarding path originates from the source address of the flow, which is 172.16.20.1 destined to the 172.16.10.1. Figure 7-27 traces the path of the data packet from the source to the destination.

Figure 7-27. Data Forwarding in Option 3

[View full size image]

Configuration Flowchart to Implement Option 3

Figure 7-28 shows the configuration steps that are involved in accomplishing a functional Inter-AS network using option 3.

Figure 7-28. Configuration Steps for Option 3

[View full size image]

Configuration and Verification of Option 3

The steps to implement option 3 for the topology shown in Figure 7-26 are as follows:

Step 1.

Configure ASBRs for eBGP and IPv4 label exchange—Configure the ASBR Routers ASBR1-AS1 and ASBR2-AS2 for eBGP. Use the neighbor send-label command to enable exchange of IPv4 label exchange between the two peers. Example 7-18 demonstrates the step.

Example 7-18. Configure ASBRs for eBGP and IPv4 Label Exchange

ASBR1-AS1(config)#router bgp 1

ASBR1-AS1(config-router)#no bgp default route-target filter

ASBR1-AS1(config-router)#neighbor 172.16.3.2 remote-as 2

ASBR1-AS1(config-router)# neighbor 172.16.3.2 send-label

_____________________________________________________________________

ASBR2-AS2(config)#router bgp 2

ASBR2-AS2(config-router)#no bgp default route-target filter

ASBR2-AS2(config-router)#neighbor 172.16.3.1 remote-as 1

ASBR2-AS2(config-router)# neighbor 172.16.3.1 send-label

Step 2.

Route redistribution and filtering on ASBR—In this step, the loopbacks on PE1-AS1 (10.10.10.101) and P1-AS1 (10.10.10.200) are advertised in BGP so that they can be advertised to ASBR2-AS2. At ASBR2-AS2, PE1-AS1 and P1-AS1-RR loopbacks are redistributed in IGP. Example 7-19 illustrates this step.

Example 7-19. Route Redistribution and Filtering on ASBR

ASBR1-AS1(config)#router ospf 1

ASBR1-AS1(config-router)# redistribute bgp 1 subnets route-map bgp-to-ospf

ASBR1-AS1(config)#router bgp 1

ASBR1-AS1(config-router)# network 10.10.10.101 mask 255.255.255.255

ASBR1-AS1(config-router)# network 10.10.10.200 mask 255.255.255.255

ASBR1-AS1(config)#ip prefix-list pref-from-AS2 seq 1 permit 10.20.20.101/32

ASBR1-AS1(config)#ip prefix-list pref-from-AS2 seq 2 permit 10.20.20.200/32

ASBR1-AS1(config)#route-map bgp-to-ospf permit 10

ASBR1-AS1(config-rmap)#match ip address prefix-list pref-from-AS2

___________________________________________________________________________

ASBR1-AS2(config)#router ospf 2

ASBR1-AS2(config-router)# redistribute bgp 2 subnets route-map bgp-to-ospf

ASBR2-AS2(config)#router bgp 1

ASBR2-AS2(config-router)# network 10.20.20.101 mask 255.255.255.255

ASBR2-AS2(config-router)# network 10.20.20.200 mask 255.255.255.255

ASBR2-AS2(config)#ip prefix-list pref-from-AS1 seq 1 permit 10.10.10.101/32

ASBR2-AS2(config)#ip prefix-list pref-from-AS1 seq 2 permit 10.10.10.200/32

ASBR2-AS2(config)#route-map bgp-to-ospf permit 10

ASBR2-AS2(config-rmap)#match ip address prefix-list pref-from-AS1

Step 3.

Configure MP-eBGP session between the RRs—In this step, an MP-eBGP session is configured between the RR, as shown in Example 7-20. Before performing this step, ensure that the loopback addresses on the RRs are reachable by ping.

Example 7-20. Configure MP-eBGP Session Between the RRs

P1-AS1-RR(config)#router bgp 1

P1-AS1-RR(config-router)#neighbor 10.20.20.200 remote-as 2

P1-AS1-RR(config-router)#neighbor 10.20.20.200 update-source loopback0

P1-AS1-RR(config-router)#neighbor 10.20.20.200 ebgp-multihop

P1-AS1-RR(config-router)#address-family vpnv4

P1-AS1-RR(config-router-af)#neighbor 10.20.20.200 activate

P1-AS1-RR(config-router-af)#neighbor 10.20.20.200 send-community extended

_________________________________________________________________________

P1-AS1-RR(config-router-af)#neighbor 10.20.20.200 next-hop-unchanged

P1-AS2-RR(config)#router bgp 1

P1-AS2-RR(config-router)#neighbor 10.10.10.200 remote-as 2

P1-AS2-RR(config-router)#neighbor 10.10.10.200 update-source loopback0

P1-AS2-RR(config-router)#neighbor 10.10.10.200 ebgp-multihop

P1-AS2-RR(config-router)#address-family vpnv4

P1-AS2-RR(config-router-af)#neighbor 10.10.10.200 activate

P1-AS2-RR(config-router-af)#neighbor 10.10.10.200 send-community extended

P1-AS2-RR(config-router-af)#neighbor 10.10.10.200 next-hop-unchanged

ASBR and RR Configurations in Option 3

Example 7-21 shows the ASBR configurations for ASBR1-AS1 and ASBR2-AS2 and RR configurations for P1-AS1-RR and P1-AS2-RR.

Example 7-21. ASBR and RR Configurations

hostname P1-AS1-RR

!

ip cef

!

mpls ldp router-id Loopback0

!

interface Loopback0

 ip address 10.10.10.200 255.255.255.255

!

interface Serial0/0

 description connected to PE1-AS1

 ip address 10.10.10.2 255.255.255.252

 mpls ip

!

interface Serial1/0

 description connected to ASBR1-AS1

 ip address 10.10.10.6 255.255.255.252

 mpls ip

!

router ospf 1

 router-id 10.10.10.200

 network 10.0.0.0 0.255.255.255 area 0

!

router bgp 1

 no bgp default ipv4-unicast

 neighbor 10.10.10.101 remote-as 1

 neighbor 10.10.10.101 update-source Loopback0

 neighbor 10.20.20.200 remote-as 2

 neighbor 10.20.20.200 ebgp-multihop 255

 neighbor 10.20.20.200 update-source Loopback0

 !

 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 10.20.20.200 activate

 neighbor 10.20.20.200 send-community extended

 neighbor 10.20.20.200 next-hop-unchanged

 exit-address-family

Hostname P1-AS2-RR

!

ip cef

!

mpls ldp router-id Loopback0

!

interface Loopback0

 ip address 10.20.20.200 255.255.255.255

!

interface Serial0/0

 description connected to PE2-AS2-ASBR2

 ip address 10.20.20.6 255.255.255.252

 mpls ip

!

interface Serial1/0

 description connected to PE1-AS2

 ip address 10.20.20.2 255.255.255.252

 mpls ip

!

router ospf 2

 router-id 10.20.20.200

 network 10.0.0.0 0.255.255.255 area 0

!

router bgp 2

 no bgp default ipv4-unicast

 neighbor 10.10.10.200 remote-as 1

 neighbor 10.10.10.200 ebgp-multihop 255

 neighbor 10.10.10.200 update-source Loopback0

 neighbor 10.20.20.101 remote-as 2

 neighbor 10.20.20.101 update-source Loopback0

 !

 address-family vpnv4

 neighbor 10.10.10.200 activate

 neighbor 10.10.10.200 send-community extended

 neighbor 10.10.10.200 next-hop-unchanged

 neighbor 10.20.20.101 activate

 neighbor 10.20.20.101 send-community extended

 neighbor 10.20.20.101 route-reflector-client

 exit-address-family

_________________________________________________________________________

hostname ASBR1-AS1

!

ip cef

!

mpls ldp router-id Loopback0

!

interface Loopback0

 ip address 10.10.10.102 255.255.255.255

!

interface Serial0/0

 description connected to P1-AS1-RR

 ip address 10.10.10.5 255.255.255.252

 mpls ip

!

interface Serial1/0

 ip address 172.16.3.1 255.255.255.252

 mpls bgp forwarding

!

router ospf 1

 router-id 10.10.10.102

 redistribute bgp 1 subnets route-map bgp-to-ospf

 network 10.0.0.0 0.255.255.255 area 0

!

router bgp 1

 no synchronization

 network 10.10.10.101 mask 255.255.255.255

 network 10.10.10.200 mask 255.255.255.255

 neighbor 172.16.3.2 remote-as 2

 neighbor 172.16.3.2 send-label

 no auto-summary

!

ip prefix-list pref-from-AS2 seq 1 permit 10.20.20.101/32

ip prefix-list pref-from-AS2 seq 2 permit 10.20.20.200/32

!

route-map bgp-to-ospf permit 10

 match ip address prefix-list pref-from-AS2

__________________________________________________________________________

hostname ASBR2-AS2

!

ip cef

!

mpls ldp router-id Loopback0

!

interface Loopback0

 ip address 10.20.20.102 255.255.255.255

!

interface Serial0/0

 description connected to P1-AS2-RR

 ip address 10.20.20.5 255.255.255.252

 mpls ip

!

interface Serial1/0

 ip address 172.16.3.2 255.255.255.252

 mpls bgp forwarding

!

router ospf 2

 router-id 10.20.20.102

 redistribute bgp 2 metric 1 subnets route-map bgp-to-ospf

 network 10.0.0.0 0.255.255.255 area 0

!

router bgp 2

 no synchronization

 network 10.20.20.101 mask 255.255.255.255

 network 10.20.20.200 mask 255.255.255.255

 neighbor 172.16.3.1 remote-as 1

 neighbor 172.16.3.1 send-label

 no auto-summary

!

ip prefix-list pref-from-AS1 seq 1 permit 10.10.10.200/32

ip prefix-list pref-from-AS1 seq 2 permit 10.10.10.101/32

!

route-map bgp-to-ospf permit 10

 match ip address prefix-list pref-from-AS1

Verifying Inter-Provider VPN Operation Using Option 3

The steps to verify inter-provider VPN operation using option 3 are

Step 1.	Verify control plane forwarding?a class="docLink" href="#ch07fig29">Figure 7-29 shows the control plane forwarding operation when the 172.16.10.0/24 prefix is propagated across the multiprovider networks AS1 and AS2 to CE2-A. Figure 7-29. Verify Control Plane Forwarding Using Option 3 [View full size image]
Step 2.	Verify data forwarding?a class="docLink" href="#ch07fig30">Figure 7-30 shows the data forwarding path taken by 172.16.20.1 to reach 172.16.10.1. Figure 7-30. Verify Data Forwarding Using Option 3 [View full size image]
Step 3.	Verify end-to-end connectivity via ping—Verify end-to-end connectivity between Customer A networks (172.16.10.0/24 and 172.16.20.0/24) and Customer B networks (192.168.10.0/24 and 192.168.20.0/24). Example 7-22 shows the result of the ping operation. Example 7-22. 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 = 140/140/140 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 = 132/138/140 ms

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