Route Redistribution: Protocol Rules + EIGRP Redistribution

What is Route Redistribution?

“Route redistribution is simply the process of taking routes from one source and placing them into another routing domain. That source doesn’t have to be a dynamic routing protocol – we can redistribute directly connected networks and static routes.” – Chris Bryant – The Bryant Advantage

2 Caveats:

  1. The more route redistribution you perform in a given network, the greater the chance of routing loops. That’s especially true when you’re redistributing between networks with multiple entrance / exit points.
  2. Some protocols require seed metrics; others don’t. Some require you to configure a default metric; some don’t. The rules aren’t complex, but they are vital.

In a hub and spoke topology, with 3 routers, there’s no reason for the LAN to have individual routes for any destinations across the WAN, to the remote spoke routers LAN. There’s really no reason for the WAN routers to have paths to the LAN networks, and it could pose a security issue for outside routers to know exactly what network numbers we’re using on our LAN – that makes attacking our WAN that much easier.

If we wanted communication between the 2 remote spoke routers via the hub, then we would setup redistribution.

Automatic Route Redistribution Scenarios

  • IGRP automatically redistributes with EIGRP when both run the same AS number.
  • EIGRP for AppleTalk automatically redistributes between EIGRP and RTMP (Routing Table Management Protocol, an AppleTalk routing protocol).
  • EIGRP for IPX will automatically redistribute between IPX for RIP (Internetwork Packet Exchange, a networking protocol used by Novell NetWare).

If a router is running 2 instances of EIGRP, then by default there is NO auto redistribution. (The same applies for OSPF)

  • EIGRP internal AD = 90
  • EIGRP external AD after redistribution = 170



Author: drbabbers - my personal journey to ccie