In the IOS version that I use on my 2621 routers, when I use the ip default-network command and flag one of the major classful networks that I have as a candidate default. It propagtes a default route to its neighbors in the same routing domain leaving its own gateway of last resort as 'not set'. Neighbors have their gateway of last resort set to be 0.0.0.0 via <next-hop> when using RIP.
If instead of specifying only a major network number, I specify a subnet and major network number in two separate ip default-network commands - strange things happen.
1) The gateway of last resort of the local router changes to the major network via subnet specified in ip default-network.
2) A static route that can only be removed using no ip default-network <subnet> appears in the config.
3) It no longer propagates the default route - which I thought was the point of this command.
Can anyone explain the purpose of providing a subnet for the ip default-network command? I don't get it.