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Configure VRF-lite | Page 9
Understanding VRF-lite
Static and dynamic inter-VRF routing
As mentioned above, "Inter-VRF communication" on page 8, in some circumstances it is
required to (selectively) allow traffic between two interfaces that are not in the same VRF.
This will be useful if there is common network equipment (e.g. Internet connections or
shared resources) that multiple VRFs need to share.
Inter-VRF routing is achieved by statically or dynamically taking a route entry and its next-hop
interface from one VRF, and adding it into the routing table of another. A dynamic inter-VRF
route can be added by using the BGP route import/export feature. A static inter-VRF route
can be added by a user command. For more information on static routing, see "Static inter-
VRF routing" on page 17.
Static and dynamic inter-VRF communication can be used simultaneously or separately.
Dynamic inter-VRF communication is only achieved via use of the BGP routing protocol.
OSPF and RIP cannot be used to achieve inter-VRF communication.
Internally transferring routes between VRF instances is quite separate from the sharing of
routes of a specific VRF routing domain, with external routers that are members of that same
domain. As mentioned above, all dynamic routing protocols can be used to distribute routing
information to external peer devices. OSPF, RIP, and BGP can all be used to dynamically
distribute routes to external peers within VRF routing domains.
When BGP is used for dynamic inter-VRF communication, routes from other routing
protocols (including connected routes, static routes, OSPF or RIP) are redistributed into a
VRF instance’s BGP route table (BGP must be configured and associated with the VRF
instance). Other VRF instances that are configured with BGP can selectively copy these
routes into their own separate BGP route tables.
Inter-VRF route leakage interoperates with the exchange of route information. Routes learnt
from external peers in one VRF domain can be leaked to other VRF instances and routes
leaked into a VRF instance can then be advertised to external peers connected to that
instance.
The details of dynamic inter-VRF routing are described in "Dynamic inter-VRF communication
explained" on page 18.