Why do my GRE go down?

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Jan 14th, 2008
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I have a DMVPN hub and spoke network. EIGRP neighbor adjacencies are established through the GRE tunnel. Sometime I get the following log:

%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor (Tunnel0) is down: holding time expired

Why is my GRE tunnel go down just because the neighbor adjacency is lost? Thanks

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Thia message is generated when you onfiguer eigrp-log-neighbor-changes in the EIGRP process, so you will be able to tell when your neighbor are having issues. There are reason other than a link failuer that will generate these messages. have a look at the document below from cisco concerning these messages it should help you understand them better. the route loss is normal on a GRE tunnel because EIGRP does not trust neighbors that exceed the timer. HTH

1. %DUAL-5-NBRCHANGE: [chars] [dec]: Neighbor [chars] ([chars]) is [chars]: [chars]

A neighbor has gone up or down.

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Richard Burts Mon, 01/14/2008 - 20:12
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I believe that there are two different issues possibly involved and that your question blurs the distinction between the issues. One issue is whether the EIGRP neighbor relationship is going down and the other issue is whether the GRE tunnel is going down.

The error message in your post indicates that the EIGRP neighbor relationship running over the tunnel has gone down and it appears that the reason is that the neighbor has missed too many keepalives. This may indicate some amount of packet loss over the GRE tunnel.

The question that your post asks is why your GRE tunnel is going down. But I do not see anything in the post that indicates that the GRE tunnel has really gown down.




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