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Point to Point connections over Ethernet

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vaniello

IS-IT--Management
Joined
Dec 21, 2004
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183
Location
US
We have several WAN connections that are point to point, but the carrier provides an Ethernet handoff to our equipment. One problem with this setup is that if the long haul portion of the circuit goes down our router interface stays up. We use a routing protocol to route around the down circuit, but since our router interface stays up we can not easily detect that the circuit is down.

Is there anyway to have the Ethernet interfaces go down when they can no longer reach the other end of the connection? Would a GRE tunnel or something similar over the connection work for this and then we can detect when the tunnel goes down instead? If so, what would be the pros and cons of doing this.

Thanks.

V/
 
Yeap you need to use object tracking, a newer IOS feature, on your gre tunnel:


If you have two routers it would be easier, you can use HSRP and the track command, and track your gre tunnel (from the loopback on the remote router to the loopback on the core router), if the int goes down the priorty drops, and the ISDN router takes precidence and comes up, dialing round the cloud.

UnaBomber
ccnp mcse2k
 
We use a routing protocol to route around the down circuit, but since our router interface stays up we can not easily detect that the circuit is down.

If you use a routing protocol then I can't see why you have a problem? If the interface stays up but the routing adjacency fails then the routes will be removed from the routing table and any alternate routes should be installed to replace the failed one(s).

Are you sure you have a routing protocol and your not just using static/default routes?

Andy
 
Since you say "Would a GRE tunnel or something similar over the connection work...", I gather that you don't have one now.

Yes, implementing a GRE tunnel would fix it. I don't have experience with object tracking, but have used GRE with EIGRP.

A GRE tunnel creates virtual interfaces like "Tu0" which will go down if the tunnel is down for any reason, including link failure at the remote end.
 

ADB100-

The issue is that our network monitoring system does not detect the failure since the Ethernet interface is still up and therefore we are not immediately alerted when there is a connection problem.

V/
 
Ohh I see you want to monitor.

We use a routing protocol to route around the down circuit, but since our router interface stays up we can not easily detect that the circuit is down.

This is confusing indeed, you route around the down part of the circuit, but you want to monitor a part of the circuit that isnt down? Do you own the circuit end to end? Why not monitor the circuit end to end, so you can see which part goes down?

I have to agree with Andy and further say that a gre tunnel will not go down unless your circuit breaks, however if part breaks and is routed round the gre tunnel will go down for the period that it takes for convergence to happen. It would have the same behaviour as an icmp ping to the remote router, it would time out until convergence has happened.

Initially when I read your post I was assuming you were talking about redundancy to another circuit if your primary went down, even for a fraction of a second.



UnaBomber
ccnp mcse2k
 
The issue is that our network monitoring system does not detect the failure since the Ethernet interface is still up and therefore we are not immediately alerted when there is a connection problem.

I assume you are running a routing protocol other than RIP or IGRP and a break in an adjacency with a neighbor will be logged. Therefore your management station should be able to flag this as an event/error based on the Syslog message or SNMP trap?

Andy
 
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