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