Friday, April 27, 2012

Propagating Default Routes - EIGRP

There are 4 ways to get default routes into EIGRP topology. We will take a look at all of them. Consider a simple 2 router topology and let's begin.

1) Redistributing static into EIGRP.

  • Get interfaces configured 
  • Add a default static route pointing to null0 on R2
  • Redistribute static into EIGRP and notice that R3 now uses R2 as default gateway. 

2) ip default-network

  • R2 loopback 1 with the default gateway 
  • R2 loopback 2 with an extra network just to test
  • R2 ip default-network command
  • R2 eigrp 100 to send advertisement. 
  • Notice that in R3 appears with a *
  • Notice that R3 can ping (lo on R2) by using a default route. 

3) Summary address 
  • ip summary-address eigrp <ASN> <ad|leak-map>
  • Notice that in R3 there is just a default and no other specific routes. 
  • Notice that in R2 a summary route was created pointing to null0
  • Context help and notice leak-map. 
  • Leak-map are similar to route-maps and you can configure a subset of routes that are leaked via summary-addresses. 
4) network everything by typing network under the eigrp process. Thanks to Anonymous for the comment.
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  1. Once saw a fourth way to do that: use "network" on EIGRP process.

    All the connected routes get distributed in EIGRP (and not redistributed).

    I don't now if it is an intended feature, or just an idiosyncrasy of that IOS version.

    1. Thank you and appreciate the comment. I tested it and it does work. Post has been amended accordingly. Although this process is not very well documented.

      Good catch.

      Arwin R.