VLAN IDs from different VRFs are mapped into different policy labels, which are used to distinguish the VRFs during processing. For each new VPN route learned, the Layer 3 setup function retrieves the policy label by using the VLAN ID of the ingress port and inserts the policy label and new route to the multi-VRF CE routing section. If the packet is received from a routed port, the port internal VLAN ID number is used; if the packet is received from an SVI, the VLAN number is used. Packet-Forwarding Process This is the packet-forwarding process in a multi-VRF-CE-enabled network:
• When the switch receives a packet from a VPN, the switch looks up the routing table based on the input policy label number. When a route is found, the switch forwards the packet to the PE. • When the ingress PE receives a packet from the CE, it performs a VRF lookup. When a route is found, the router adds a corresponding MPLS label to the packet and sends it to the MPLS network. • When an egress PE receives a packet from the network, it strips the label and uses the label to identify the correct VPN routing table. Then it performs the normal route lookup. When a route is found, it forwards the packet to the correct adjacency.
• When a CE receives a packet from an egress PE, it uses the input policy label to look up the correct VPN routing table. If a route is found, it forwards the packet within the VPN. Network Components To configure VRF, you create a VRF table and specify the Layer 3 interface associated with the VRF. Then configure the routing protocols in the VPN and between the CE and the PE. BGP is the preferred routing protocol used to distribute VPN routing information across the provider’s backbone. The multi-VRF CE network has three major components: • VPN route target communities—lists of all other members of a VPN community. You need to configure VPN route targets for each VPN community member.
• Multiprotocol BGP peering of VPN community PE routers—propagates VRF reachability information to all members of a VPN community. You need to configure BGP peering in all PE routers within a VPN community. • VPN forwarding—transports all traffic between all VPN community members across a VPN service-provider network. VRF-Aware Services IP services can be configured on global interfaces, and these services run within the global routing instance. IP services are enhanced to run on multiple routing instances; they are VRF-aware. Any configured VRF in the system can be specified for a VRF-aware service. VRF-Aware services are implemented in platform-independent modules.
VRF means multiple routing instances in Cisco IOS. Each platform has its own limit on the number of VRFs it supports. VRF-aware services have the following characteristics: • The user can ping a host in a user-specified VRF. • ARP entries are learned in separate VRFs. The user can display Address Resolution Protocol (ARP) entries for specific VRFs. Configuring Multi-VRF CE Packet-Forwarding Process Configuring Multi-VRF CE 3