Default route

Unanswered Question
Jun 2nd, 2009

Hi,

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.

Thanks

Rajesh

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Giuseppe Larosa Tue, 06/02/2009 - 21:57

Hello Rajesh,

the PE node has proxy-arp disabled.

when you use the second type of static route you are not relying on PE node settings.

It is more correct in a LAN interface to specify the IP next-hop.

We had an issue on a network for this reason: there were routers terminating PPP sessions that were using default static routes pointing to lan interface.

After a security assessment ip proxy-arp was disabled on core router and the other routers could not route anymore: specifying the IP next hop the problem was fixed.

Hope to help

Giuseppe

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