EIGRP Auto-Summary

EIGRP Auto-Summary of INE workbook

Why is the routing table Null0 disappear when shutdown loopback 0?
Why do you have null0 inserted and sometimes not inserted when auto-summary is enabled?

Answers

  • well, I guess this comes pretty late now, but I will still give it a try :smiley:

    maybe you could share some topology information regarding the disappearing Null0 route when you shutdown your Loopback IF.

    whenever you do summarization the router will crate a Null0 route automatically to prevent loops in the network. Let's say I have the more specific routes and I announce a summary 10.1.0.0/16 to you. This means (if you have no better choice) you will route any traffic from that /16 towards me. If I lose a more specific route because of an interface going down or something the Null0 route would make me punt that packet to the CPU and finally drop it, so that I will not route that towards my default route or another summary where it potentially gets routed back towards me and we have created a loop.

    i hope this makes sense

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