I have come across an interesting situation and had some argument with colleagues and still I can't find out the solution. I hope some one might have an answer for this.
I have attached the scenario diagram and it will be helpful to describe better. As indicated in the diagram, there is a head end router with a 10 M connection and a remote router with an ADSL link. In this scenario I am not using any routing protocols and only using default routing.
The problem here is, on the head end while defining a default route if I use Gig 0/0 as the outgoing interface I cant ping the ADSL router's LAN or WAN IP. But if I used the next hop's address(PE's 10.5.15.70) I can ping the remote routers IP. But, in the ADSL router I always pointed the dialer interface while defining a default router and its sweet.
According to the design/diagram -
ip route 0.0.0.0 0.0.0.0 gigabitEthernet 0/0 - not working
ip route 0.0.0.0 0.0.0.0 10.5.15.70 - Working fine
This is not a major issue, but our of curiosity and to understand things better I am posing this question.