CCNP

Redistribution : Common Language Of Routing Protocols

redistribution

In this article we will deeply check redistribution. First of all we need to know “why redistribution is used”. We use “redistribution” , to have a communication between different routing protocols. For example if we are using multiple protocols like EIGRP , OSPF and etc. and want communication between these protocols, we should use redistribution.

WHY WE NEED MULTIPLE PROTOCOLS ?

1) Flexibility is required for some networks.
2)
For convertion between routing protocols.
3)
Vendor choices.
4)
Application requirements.

redistribution

We need to implement redistribution to have a communication between different routing protocol networks.

REDISTRIBUTION PROBLEMS

redistribution problems

Some problems may occur when we implement redistribution ;

* Redistribution should be made just for one direction. For example if we are sending EIGRP routes to OSPF domain, these routes aren’t sent back to EIGRP domain but this time EIGRP domain can’t learn OSPF routes. This is one of the problems that we can face.

* For example assume that we are making double directed redistribution on router 1. External routes come to EIGRP domain ( AD = 170 ). After they are forwarded to router 2 which is in OSPF domain. Router 2 can go from two different paths ( OSPF or EIGRP ). Because of OSPF’s default AD is 110, Router 2 returns back to Router 3 over Router 1 and uses a bandwith of 14.4 kbps which is very slow.

We can solve these issues using the items below ;

1) Passive interface
2) AD Modification
3)
Distribute List/Prefix List

For example Distribute list can distribute just the 10.1.x.x or 10.2.x.x network. For another example Prefix list can distribute the networks between /16 to /24.

 4) Route Maps / Route tagging

redistribution

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