When I configure an OSPF router with "default-information originate always", that router starts to unconditionally announce 0.0.0.0/0 route -- but the router itself will no longer have 0.0.0.0/0 router from other router(s) in its route table. See following output (abbreviated, the router has Lo0 = 192.168.0.2, 192.168.0.1 is other directly connected router):
Router#sh ip ospf database
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
0.0.0.0 192.168.0.1 851 0x80000001 0x00291F 1 <-- other router's def.route
0.0.0.0 192.168.0.2 692 0x80000001 0x002324 1
Router#sh ip ro
Gateway of last resort is not set <-- I have 0.0.0.0/0 from rtr 192.168.0.1 in my DB, but not in RT
C 192.168.0.0/24 is directly connected, FastEthernet1/0
I don't quite get the logic of this behaviour and I couldn't find any explanation. The thing is, that my company has routing setup where this actually causes black hole routing, when one of the default-route-propagating routers loses its BGP routes.
Can someone enlighten me?