Redistribution imports routes from one protocol to another. Redistribution sends route updates for a protocol-based route through another protocol. For example, if OSPF routes exist in a router and they must travel through a BGP network, then configure redistribution of OSPF routes through BGP. This sends OSPF routes to a router that uses BGP.
The switch can redistribute routes:
on an interface basis.
on a global basis between protocols on a single VRF instance (intraVRF).
between the same or different protocols on different VRF instances (interVRF).
Configure interface-based redistribution by configuring a route policy and apply it to the interface. Configure the match parameter to the protocol from which to learn the routes.
You can redistribute routes on a global basis, rather than on an interface basis. Use the ip bgp redistribute command to accomplish the (intraVRF) redistribution of routes through BGP, so that BGP redistribution occurs globally on all BGP-enabled interfaces. This redistribution does not require a route policy, but you can use one for more control.
If you configure redistribution globally and on an interface, redistribution through the route policy takes precedence.
You can redistribute routes from a protocol in one VRF to BGP in another VRF. You can use a route policy for redistribution control. If you enable route redistribution between VRF instances, ensure that IP addresses do not overlap.
Use caution when you configure redistribution. An improperly configured parameter can cause the router to advertise learned eBGP routes out of your local AS. If this happens, the local AS can route other networks.
Do not use redistribution if you peer to an Internet Service Provider (ISP) and do not want traffic to transit your local AS.
When you redistribute OSPF routes into BGP, route priorities can create routing loops. Because BGP has a higher route preference than OSPF external type 1 and 2 routes, if you redistribute OSPF external type 1 and 2 routes into BGP, the router uses the BGP routes, which can cause a routing loop.
BGP Routing Information Base (BGP RIB) stores routing information received from different peers. BGP RIB has two types of BGP routes, External and Internal (Local). The routes learned from BGP neighbors are External routes and all imported routes are considered as Internal (Local) routes.
In BGP RIB, the OSPF routes redistributed into BGP are considered as Internal (Local) and are matched by route-type only when the keyword is set to local. When match route-type is set to external, the route-maps applied on BGP neighbors are ignored and the set operation is not performed.
Note
This is applied only on the route-maps applied to BGP neighbors in BGP RIB, and not considered when applying a route-map to the redistribute command.
DvR Controllers redistribute routes (direct routes, static routes and the default route) into the DvR domain. You can configure redistribution of DvR host routes into BGP.
For information on DvR, see Distributed Virtual Routing.