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New Member

Routing Problem

To me, this seems to be a simple problem, and I can't understand what's going wrong.

At one site, there is the following IP scheme in place:

172.16.1.0

172.16.2.0

172.16.15.0

At another site the following IP scheme is in place

172.17.1.0

On the 172.17.1.1 router, there is a route to the network

IP Route 172.16.0.0 255.255.0.0

From the 172.17.1.0 network, I get a destination unreachable when I try to ping anything on 172.16.2.0. The 172.16.1.1 router has IP ROUTE 172.17.0.0 255.255.0.0 in place.

Could this be an access list entry at one of the routers? The previous network engineer had a lot of unnecessary access list entries in both routers that I'm trying to sort through...

The real question is.... will I get destination unreachable because an access list entry is filtering the packets, or is the only way I'll get destination unreachable is because of a routing failure?

I realize this is an elementary question, but please bear with me, as I'm cleaning up a big mess here.

4 REPLIES
New Member

Re: Routing Problem

b-chase,

It sounds like you're using all static routes here. Try using extended ping and trace from the routers, using the ethernet port's IP address as the source address. If you see "A" in an extended trace , it means that an Access-List is filtering out the packet. Trace will also help, the next hop after the last responding hop is the one that does know how to either get to the destination address or more likely return to the source address.

Regards,

Rob Bristow

AT&T Solutions

CCIE #3335

New Member

Re: Routing Problem

Rob,

Thank you. That's just what I was looking for.

Ben Chase

Re: Routing Problem

ICMP unrechables are sent by a router (except a few L3 switches) when a packet is denied by an ACL. In your case, it could be due to that. If you can paste the configs of ACL, we might be able to help!

Just to verify, it there is any routing problems, are you facing problems pinging other subnets in the 172.16.0.0 range ?

New Member

Re: Routing Problem

Unfortunately, I cannot paste the configs of either router due to my work environment.

We don't have any other routing problems....I can ping 172.16.1.0 no problem.. 172.16.2.0 was the one with the problem...and after verifying the correct netmask, I suspected the ACL.

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