Fundamentals Of Route Redistribution

Golden Rules about Route Redistribution:-
1. Routes can be redistributed from one routing protocol to another. This is the assumption which we are working. But this is not true, routes are not redistributed from one protocol to another. Routes are always taken from RIB not from a routing protocol.

2. The redistributing protocol knows which routes to take from the RIB based on the “known via” information present in "show ip route" details.

3. A route must be installed in the RIB for it to be redistributed in another protocol.

4. Routes redistributed from the routing table are not re-installed again into the RIB.

5. Only the attributes of a route present in the RIB can be used for filtering.

Redistribution Filters:-
1. Redistribution filters can control what information is injected into a routing protocol through redistribution.

2. Filters can also be used to stop routing loops(Read more about layer 3 routing loops) when mutual redistribution between two routing protocols is configured.

Redistribution Filter Tools:-
1. Match metric:- Filtering is possible between all protocols based on metric used.

2. Match Tag:- While mutual redistribution, TAGs can be assigned to routes to stop the routing loop too.

3. Match IP Address:- Matches the prefix, possibly the network mask, depending on the access list type used.

4. Match IP Next Hop Address:- Matches on the next hop listed in the routing table.

5. Match route-type

6. Match Interface

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