ip route to dhcp remains in configuration after wr with AD 254

2044418Puts · ‎08-12-2012

Hi,

I'm running several routers with the 15.1(4)M4 IOS and they all face this issue:

The ethernet WAN link is configured with an DHCP address, so the default route has been configured as follows: "ip route 0.0.0.0 0.0.0.0 dhcp"

The strange thing is that when the WAN link comes up and gets a default gateway of lets say 1.1.1.1 the the "show run" starts to look like this:

ip route 0.0.0.0 0.0.0.0 dhcp

ip route 0.0.0.0 0.0.0.0 1.1.1.1 254

There is a new static added with an AD of 254 to the running configuration. As soon as I save this configuration this entry is saved as well and remains there even after a reload. So if I would get another gateway from the DHCP server (lets say 2.2.2.2) my configuration looks like this:

ip route 0.0.0.0 0.0.0.0 dhcp

ip route 0.0.0.0 0.0.0.0 1.1.1.1 254

ip route 0.0.0.0 0.0.0.0 2.2.2.2 254

So my configuration is starting to fill up with default routes. This might just be cosmetic since only the route that has its gateway in a directly connected subnet is installed in the routing table. But my question is, is this normal behaviour?

Thanks!

Peter Paluch · ‎08-12-2012

Hello,

Definitely, this is not a normal behavior. In fact, the default routes should be added with AD 1, not AD 254 - because of the static "ip route 0.0.0.0 0.0.0.0 dhcp" command.

There seems to be a number of bugs recorded in Cisco's bug database that describe similar issues, although I have not been able to find exactly the one you describe here.

In any case, two suggestions:

Try upgrading the IOS if possible
Try removing the ip route 0.0.0.0 0.0.0.0 dhcp from your configuration altogether. It has been my experience that regardless of the presence of this command, the default route will be added to your routing table automatically. Perhaps the lack of this static default route in your running configuration will prevent the router from adding the DHCP-discovered default routes into your running-config.

And of course, if you do have a support contract with Cisco, be sure to inform them about this!

Best regards,

Peter