EIGRP Autonomous Systems

[edstacey]

In a network that has LAN and WAN links with EIGRP as the routing protocol, is it best practice to have a separate Autonomous System for the LAN (LAN devices with L3 capability) and a separate Autonomous System for the WAN where there are 20 WAN connections? If so, what are the benefits? Currently, all sites (LAN and WAN) have a single Autonomous System.

[vmiller]

If the network in question is administrativly owned by one group, then I would say no. Splitting AS's would partition the network.

[Gilles Dufour]

The only reason I can see to do such a thing is if your WAN network is unstable and you want to protect the rest of the networks.

However, if you do a good summarization, you should achieve the same protection without having 2 processes.

It is also recommended to avoid multiple processes since they usually come with redistribution between 1 and the other which can lead to routing loops.

So, I would say, go with 1 AS and use summary.

Or go with OSPF or ISIS to have a real Link state protocol and are partitioning.