MPLS VPN - Route Target Rewrite
The MPLS VPN—Route Target Rewrite feature allows the replacement of route targets on incoming and outgoing Border Gateway Protocol (BGP) updates. Typically, Autonomous System Border Routers (ASBRs) perform the replacement of route targets at autonomous system boundaries. Route Reflectors (RRs) and provider edge (PE) routers can also perform route target replacement.
The main advantage of the MPLS VPN - Route Target Rewrite feature is that it keeps the administration of routing policy local to the autonomous system.
Prerequisites for MPLS VPN - Route Target Rewrite
The MPLS VPN - Route Target Rewrite feature requires the following:
•You should know how to configure Multiprotocol Virtual Private Networks (MPLS VPNs).
•You need to configure your network to support interautonomous systems (Inter-autonomous system) with different route target (RT) values in each autonomous system.
•You need to identify the RT replacement policy and target router for each autonomous system.
Restrictions for MPLS VPN - Route Target Rewrite
You can apply multiple replacement rules using the route-map continue clause. The MPLS VPN - Route Target Rewrite feature does not support the continue clause on outbound route maps.
Information About MPLS VPN - Route Target Rewrite
To configure the MPLS VPN - Route Target Rewrite feature, you need to understand the following concepts:
• Route Target Replacement Policy
• Route Maps and Route Target Replacement
Route Target Replacement Policy
Routing policies for a peer include all configurations that may impact inbound or outbound routing table updates. The MPLS VPN - Route Target Rewrite feature can influence routing table updates by allowing the replacement of route targets on inbound and outbound BGP updates. Route targets are carried as extended community attributes in BGP Virtual Private Network IP Version 4 (VPNv4) updates. Route target extended community attributes are used to identify a set of sites and VPN routing and forwarding (VRF) instances that can receive routes with a configured route target.
In general, ASBRs perform route target replacement at autonomous system borders when the ASBRs exchange VPNv4 prefixes. You can also configure the MPLS VPN - Route Target Rewrite feature on PE routers and RR routers.
Figure 1 shows an example of route target replacement on ASBRs in an MPLS VPN Inter-autonomous system topology. This example includes the following configurations:
•PE1 is configured to import and export RT 100:1 for VRF VPN1.
•PE2 is configured to import and export RT 200:1 for VRF VPN2.
•ASBR1 is configured to rewrite all inbound VPNv4 prefixes with RT 200:1 to RT 100:1.
•ASBR2 is configured to rewrite all inbound VPNv4 prefixes with RT 100:1 to RT 200:1.
Figure 1 Route Target Replacement on ASBRs in an MPLS VPN Inter-AS Topology
Figure 2 shows an example of route target replacement on route reflectors in an MPLS VPN Inter-autonomous system topology. This example includes the following configurations:
•EBGP is configured on the route reflectors.
•EBGP and IBGP IPv4 label exchange is configured between all BGP routers.
•Peer groups are configured on the routers reflectors.
•PE2 is configured to import and export RT 200:1 for VRF VPN2.
•PE2 is configured to import and export RT 200:2 for VRF VPN3.
•PE1 is configured to import and export RT 100:1 for VRF VPN1.
•RR1 is configured to rewrite all inbound VPNv4 prefixes with RT 200:1 or RT 200:2 to RT 100:1.
•RR2 is configured to rewrite all inbound prefixes with RT 100:1 to RT 200:1 and RT 200:2.
Figure 2 Route Target Rewrite on Route Reflectors in an MPLS VPN Inter-autonomous system Topology
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The main advantage of the MPLS VPN - Route Target Rewrite feature is that it keeps the administration of routing policy local to the autonomous system.
Prerequisites for MPLS VPN - Route Target Rewrite
The MPLS VPN - Route Target Rewrite feature requires the following:
•You should know how to configure Multiprotocol Virtual Private Networks (MPLS VPNs).
•You need to configure your network to support interautonomous systems (Inter-autonomous system) with different route target (RT) values in each autonomous system.
•You need to identify the RT replacement policy and target router for each autonomous system.
Restrictions for MPLS VPN - Route Target Rewrite
You can apply multiple replacement rules using the route-map continue clause. The MPLS VPN - Route Target Rewrite feature does not support the continue clause on outbound route maps.
Information About MPLS VPN - Route Target Rewrite
To configure the MPLS VPN - Route Target Rewrite feature, you need to understand the following concepts:
• Route Target Replacement Policy
• Route Maps and Route Target Replacement
Route Target Replacement Policy
Routing policies for a peer include all configurations that may impact inbound or outbound routing table updates. The MPLS VPN - Route Target Rewrite feature can influence routing table updates by allowing the replacement of route targets on inbound and outbound BGP updates. Route targets are carried as extended community attributes in BGP Virtual Private Network IP Version 4 (VPNv4) updates. Route target extended community attributes are used to identify a set of sites and VPN routing and forwarding (VRF) instances that can receive routes with a configured route target.
In general, ASBRs perform route target replacement at autonomous system borders when the ASBRs exchange VPNv4 prefixes. You can also configure the MPLS VPN - Route Target Rewrite feature on PE routers and RR routers.
Figure 1 shows an example of route target replacement on ASBRs in an MPLS VPN Inter-autonomous system topology. This example includes the following configurations:
•PE1 is configured to import and export RT 100:1 for VRF VPN1.
•PE2 is configured to import and export RT 200:1 for VRF VPN2.
•ASBR1 is configured to rewrite all inbound VPNv4 prefixes with RT 200:1 to RT 100:1.
•ASBR2 is configured to rewrite all inbound VPNv4 prefixes with RT 100:1 to RT 200:1.
Figure 1 Route Target Replacement on ASBRs in an MPLS VPN Inter-AS Topology
Figure 2 shows an example of route target replacement on route reflectors in an MPLS VPN Inter-autonomous system topology. This example includes the following configurations:
•EBGP is configured on the route reflectors.
•EBGP and IBGP IPv4 label exchange is configured between all BGP routers.
•Peer groups are configured on the routers reflectors.
•PE2 is configured to import and export RT 200:1 for VRF VPN2.
•PE2 is configured to import and export RT 200:2 for VRF VPN3.
•PE1 is configured to import and export RT 100:1 for VRF VPN1.
•RR1 is configured to rewrite all inbound VPNv4 prefixes with RT 200:1 or RT 200:2 to RT 100:1.
•RR2 is configured to rewrite all inbound prefixes with RT 100:1 to RT 200:1 and RT 200:2.
Figure 2 Route Target Rewrite on Route Reflectors in an MPLS VPN Inter-autonomous system Topology
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