Mpls L3Vpn Major Components; Inter-As Support For L3Vpn; Inter-As Restrictions; Inter-As Support: Overview - Cisco CRS Configuration Manual

MPLS L3VPN Major Components

With thousands of routers in a network each supporting multiple VRFs, configuration and management of
route distinguishers across the network can present a problem. Cisco IOS XR software simplifies this process
by assigning unique route distinguisher to VRFs using the rd auto command.
To assign a unique route distinguisher for each router, you must ensure that each router has a unique BGP
router-id. If so, the rd auto command assigns a Type 1 route distinguisher to the VRF using the following
format: ip-address:number. The IP address is specified by the BGP router-id statement and the number (which
is derived as an unused index in the 0 to 65535 range) is unique across theVRFs.
Finally, route distinguisher values are checkpointed so that route distinguisher assignment to VRF is persistent
across failover or process restart. If an route distinguisher is explicitely configured for a VRF, this value is
not overridden by the autoroute distinguisher.
MPLS L3VPN Major Components
An MPLS-based VPN network has three major components:
• VPN route target communities—A VPN route target community is a list of all members of a VPN
• Multiprotocol BGP (MP-BGP) peering of the VPN community PE routers—MP-BGP propagates VRF
• MPLS forwarding—MPLS transports all traffic between all VPN community members across a VPN
A one-to-one relationship does not necessarily exist between customer sites and VPNs. A given site can be a
member of multiple VPNs. However, a site can associate with only one VRF. A customer-site VRF contains
all the routes available to the site from the VPNs of which it is a member

Inter-AS Support for L3VPN

This section contains the following topics:

Inter-AS Restrictions

Inter-AS functionality is available using VPNv4 only. VPNv6 is not currently supported.

Inter-AS Support: Overview

An autonomous system (AS) is a single network or group of networks that is controlled by a common system
administration group and uses a single, clearly defined routing protocol.
As VPNs grow, their requirements expand. In some cases, VPNs need to reside on different autonomous
systems in different geographic areas. In addition, some VPNs need to extend across multiple service providers
(overlapping VPNs). Regardless of the complexity and location of the VPNs, the connection between
autonomous systems must be seamless.
An MPLS VPN Inter-AS provides the following benefits:
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community. VPN route targets need to be configured for each VPN community member.
reachability information to all members of a VPN community. MP-BGP peering needs to be configured
in all PE routers within a VPN community.
service-provider network.
Implementing MPLS Layer 3 VPNs