Configuring Inter-AS VPN Option B (ASBR Also Functioning as an RR)
In a scenario in which the backbone network spans two ASs, ASBRs need to advertise VPNv4 routes through MP-EBGP. When multiple PEs exist in the ASs, you can configure an ASBR as an RR to lower configuration complexity.
Usage Scenario
In inter-AS VPN Option B mode, if multiple PEs exist in an AS, you can configure an ASBR as an RR to reduce the number of MP-IBGP connections needed between PEs. Configuring an ASBR as an RR will burden the ASBR. Therefore, it is required that a high-performance device be used as the ASBR. On the network shown in Figure 1, ASBR1 is configured as an RR so that PE1 and PE2 do not need to set up an MP-IBGP peer relationship.
Pre-configuration Tasks
Before configuring inter-AS VPN Option B (ASBR also functioning as an RR), complete the following tasks:
Configure an IGP for the MPLS backbone network of each AS to ensure IP connectivity of the backbone network in each AS.
Configure MPLS both globally and per interface on each node of the MPLS backbone network in each AS and establish an LDP LSP or TE tunnel between MP-IBGP peers.
Configure a VPN instance on each PE and bind the interface that connects a PE to a CE to the VPN instance on that PE.
Configure an IP address for the interface connecting a CE to a PE.
- Configuring MP-IBGP Between a PE and an ASBR in the Same AS
- By introducing extended community attributes into BGP, MP-IBGP can advertise VPNv4 routes between the PE and ASBR.
- Configuring MP-EBGP Between ASBRs in Different ASs
- After an MP-EBGP peer relationship is established between ASBRs, an ASBR can advertise the VPNv4 routes of its AS to the other ASBR.
- Configuring ASBRs Not to Filter VPNv4 Routes Based on VPN Targets
- In inter-AS VPN Option B mode, ASBRs do not have VPN instances. If you want ASBRs to keep received VPNv4 routes, configure ASBRs not to filter VPNv4 routes based on VPN targets.
- (Optional) Using a Routing Policy to Control VPNv4 Routes on ASBRs
- ASBRs can use a routing policy to filter undesired VPNv4 routes.
- (Optional) Configuring One-Label-per-Next-Hop Label Distribution on an ASBR
- To save label resources on an ASBR, configure one-label-per-next-hop label allocation on the ASBR. One-label-per-next-hop label allocation on ASBRs and one-label-per-instance label distribution on PEs must be used together.
- Configuring BGP IPv4 VPN Route Reflection on an ASBR
- Route reflection on an ASBR is used to reflect the VPNv4 routes advertised by the PE in the same AS to other PEs. As a result, PEs do not need to set up BGP peer relationships, which simplifies configurations.
- Verifying the Configuration of Inter-AS VPN Option B (ASBR Also Functioning as an RR)
- After configuring inter-AS VPN Option B (ASBR also functioning as an RR), check the status of all BGP peer relationships and VPNv4 routing information on PEs or ASBRs.