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Routing issue on cisco

Posted on 2008-10-04
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Last Modified: 2010-04-17
We have a network 20.x.x.x with 200 sites running EIGRP on cisco routers. A non cisco router wants to connect to us via a T1 interface. We can ping their Serial (20.250.240.1) interface and so can they (20.250.240.2). Non cisco rtr is assigned an address of 20.1.220.x. From their network, they can ping us, but we can't. What conf changes need to be made at our end (or theirs) so that we can ping the 20.1.220.x  
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Question by:totaram
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by:Pugglewuggle
ID: 22643622
Sounds like static routes need to be added on their end since the routes aren't automatically populated by EIGRP.
Let me know if you have any questions!
Cheers!
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by:src1963
ID: 22643822
The easiest solution is to establish RIP V2 (it has to be V2 not V1 since you are using classless non-contiguous subnets) between the two routers on the ends of the T1 serial link. Your cisco router will then learn about the subnet containing the 20.1.220.X and will propagate that knowledge via EIGRP to the other cisco routers in your network. Their routers will also learn about all the subnets in your network and pass that on via whatever routing protocol they are using.  You can run more than one routing protocol on your cisco router, so running both EIGRP and RIP V2 is possible.  You can solve this with static routes as well but that is much more complex and error-prone. By the way, since your serial link is T1, you don't need to worry about additional load from RIP. It won't add much traffic to that serial link.
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by:Pugglewuggle
ID: 22643846
Yes, RIP would work, but its performance over a WAN link is questionable... meaning not bandwidth consumption (as they are T1s as mentioned) , but since RIP is a broadcast protocol it might not traverse the line without an ip directed-broadcast setup.
Try it and let us know.
Cheers!
 
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by:src1963
ID: 22645064
OK. but RIP V2 is NOT broadcast, its multicast. V1 is broadcast but not V2.  No special setup is required beyond the ROUTER RIP , VERSION 2 and NETWORK 20.0.0.0 commands.

By the way, to ensure that you don't have any "redistribution" issues with EIGRP, just run RIP V2 on ALL your routers in addition to EIGRP.  That way, the two networks (cisco and non-cisco) will be fully joined with one routing protocol (RIP V2). It costs you virtually nothing in bandwidth and processor cycles, and is brain-dead-easy to configure. You still get all the benefits of EIGRP for routes within your own Autonomous system.

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by:lrmoore
ID: 22645323
You could also simply add a static route on the T1 router and redistribute the static into EIGRP
Assuming that the other end of the T1 also has a static route for 20.1.0.0/16 pointing to your side of the T1

>From their network, they can ping us, but we can't
If they can ping you, that means that they can route packets to you and your echo-replies are being routed back. If you can't ping them, then there could be something else blocking the echo-replies on their end.

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by:totaram
ID: 22646501
Going by lrmoore reply,  will there be static routes on both sides? T1 route comes from our router.
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lrmoore earned 125 total points
ID: 22650043
Yes, both sides need static routes. "their" router needs a static route for 20.1.0.0/16 that points to your end of the T1 - 20.250.240.2
Your router needs a static route for 20.1.220.0 pointing to their end of the T1 (20.250.240.1)
I am assuming here that most of your network is in the 20.1.x.x/16 summary block..
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by:src1963
ID: 22652004
Be careful with static routes.

You must configure static routes not just to the other side of the T1 but to ALL subnets on the other side. And this must be done for routers on both sides of the T1 link.   And if any changes are made to subnets on one side, you must update the static routes on the other side.  I really think you should consider running RIP V2, as I suggested previuosly.
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by:Pugglewuggle
ID: 22652104
Like I said in my first post, the easiest thing to do on the WAN link (T1), unless you have a ridiculous amount of networks, is just to put some static routes on the WAN routers. If you do have a mad number of networks go ahead and use RIP V2.
Also regarding the "not being able to ping" make sure you have an ACL on your outside interface in the incoming direction that allows ICMP echo-reply messages.
Cheers! Let me know if you have any questions! :)
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