Routing

I was playing with EIGRP in one of our labs a while back and noticed a command that I figured would come in handy at some point.   The purpose of the command under router configuration mode is to control candidate default routes within EIGRP.   Now, there are many ways to do this and I’m more than happy to learn about a few more.   When I figured out exactly how this command works, I was a tad disappointed.   For those of you, who aren’t sure of what I’m talking about, have a look at the output:

Router(config-router)#default-information ?
 allowed   Allow default information
 in             Accept default routing information
 out           Output default routing information

When I first stumbled upon it, I immediately thought of how useful “no default-information out” might be.   Eventually, I got around to setting up a small lab with three routers to see just exactly how this command operated.     The command is not as straight forward as one might think.   After some tinkering, I was finally able to find a working configuration.   The router in the middle had this configuration:

R2#sh run | b router
router eigrp 10
 network 10.0.0.0
 network 192.168.0.0
 no default-information out
 no auto-summary
!
!
!
!
ip default-network 192.168.0.0
!

Here is router three’s configuration:

R3#sh run | b router
router eigrp 10
 network 10.0.0.0
 network 192.168.3.1 0.0.0.0
 no auto-summary
!

The only way I was able to get this command to filter default information from R3 was to identify a major classful network using “ip default-network.”   That is it.   If you are looking to have more granular control over default routes, you may be better off using a route-map or distribute-list.

-Tim