VRF: Virtual Routing & Forwarding

• VRF:
• VRF tables are the fundamental building block for virtualizing a router, it turn into multiple virtual routers.
• Technically VRF is a separate RIB(Routing Information Base) & FIB (Forward Information Base)
• Any interface on the router could be assigned to a VRF.
• using command "ip vrf forwarding <name>"
• this command will erase all existing ip address config on the interface (to avoid duplication)
• After this configuration, all packets recevied on the interface are routed & forwarded using the associated VRF table.
• VRF enabled interfaces are not showed in global routing table
• i.e show ip route
• Each VRF has its own routing table
• to see this routing table use "show ip vrf "
• Interfaces showed in global routing table are not in any vrf.
• i.e. VRF & global routes are separate.
• VRFs without MPLS is considered as "VRF Lite"
• If 2 VRFs have same ip prefix but they cannot route to each other.
• Because they are separately labeled.
• We cannot manually leak the traffic between VRFs by creating static routes.
• i.e. interfaces are route with other interfaces which are in same VRF.
• BGP is enhanced to handle VRF specific routes.
• A new sepcial MP-BGP address family named "VPN IPv4" has been added to bgp along with new NLRI format.
• To support multiple customers in MPLS VPN, VRF tables were used.
• VRF tables are used to store routes separately for different customer VPNs.
• The use of separate tables solves some problems:
• Leakage packets from one customer to another due to overlapping prefixes
• VRF has 3 main components:
• An IP routing table (RIB)
• A CEF FIB, populated based on that VRF's RIB
• A separate process of the routing protocol used to exchange routes with the CE's.
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