I have a lab scenario with 4 routers connected in a chain (RTRa->RTRb->RTRc->RTRd). RIP v1 is configured on all routers. When I configure a default route i.e 'ip route 0.0.0.0 0.0.0.0 null 0' on RTRb or RTRc the default route appears in all my routing tables automatically. If however, I place the default route on either RTRa or RTRd the route is not propagated throughout the rip domain. I have to force the issue with 'redistribute static' and all is well. Can anyone explain what is happening here ?