Network unroutable problem

Unanswered Question
May 9th, 2008

Hi Experts,

I have some strain problem. When i`m do un ping to 84.107.188.x i will get un "unroutable" message in de debug ip pack log

When i add "ip route Gateway ISP" then everything works great.

I see in the show ip route that there is a is variably subnetted. How can i fix this?


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Overall Rating: 0 (0 ratings)
Richard Burts Fri, 05/09/2008 - 11:26


I have looked at what you posted. I see what the problem is, and the fix is very easy. The essence of the problem is that 84.107.188.x is unroutable because you have another subnet of this network in the routing table: is directly connected, Dialer1 (which is the negotiated address on the Dialer) and because you have configured no ip classless. no ip classless and no ip subnet-zero are both examples of things that used to be default behavior of IOS (quite a while ago) and where the default behavior changed.

When no ip classless is configured then the router can not use the default route for an address where the router already knows some subnet in the network but not the subnet where that destination is located.

The fix is to configure the router with ip classless.

While I am at it, I notice that you have the router configured with no ip subnet-zero. That is a very old style thing to have in the config. Is there a reason for it? To conform to more modern trends in router configuration I would suggest that you configure ip subnet-zero.



supportvoiceit Fri, 05/09/2008 - 11:43

Hey Rick,

Thanks for the fast reply. I have enable ip classless en now everything works great. I also enable ip subnet-zero, but i only use 192.168.1.x/24.

I have a own business if i need some more information in the feature my i then call or e-mail you?

Thanks a lot for the fix...

Richard Burts Fri, 05/09/2008 - 12:03


I am glad that my suggestion did help you to solve your problem. If you have additional questions or problems you may get in touch with me.



sundar.palaniappan Fri, 05/09/2008 - 13:23


I have a request for you. If Rick's post helped resolve your problem could you please rate and resolve the post. That would help someone down the road, who runs into the same problem you did, quickly identify the post that provided the solution and also a recognition for the person providing assistance. I am not saying you don't want to rate the post but I see a lot of posters appreciate the help and forget to rate the post.




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