GRE tunnel problem

Unanswered Question
Sep 28th, 2009


I have MPLS link between India and US. I have configured BGP. Beside this, I have created GRE tunnel on these two point and publishing few EIGRP routes on GRE tunnel. The problem is whenever my physical link on India side is down, it shut down the tunnel also on India end. But Tunnel on US end remains up. Due to this, traffic on US routers is still forwarding EIGRP traffic to India end. As a result, no data is reachable. Please help.

I have this problem too.
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Giuseppe Larosa Mon, 09/28/2009 - 22:21

Hello Rupesh,

if you have EIGRP running on the GRE tunnel it should take up to 15/180 seconds to detect the other end has died.

check eigrp timers on GRE tunnel you may need to tune them, with LAN default values (5 seconds hello, 15 seconds hold) you should be able to detect in 15 seconds.

you can use

sh ip eigrp int tunnelx

to see these parameters

if necessary tune them on both ends because EIGRP allows for different timers on the two ends and US side waits for the time india side has declared as its hold time.

Hope to help


Rupesh Kashyap Tue, 09/29/2009 - 00:19

Hi, you understood wrong. The problem is, US end Tunnel is not down when physical link on India side is down.

Joseph W. Doherty Tue, 09/29/2009 - 04:15

I believe Giuseppe understood you. What you might not realize, GRE tunnels, by default, are "UP" even when they have no good connection to the other side. Two solutions are, when running dynamic routing (e.g. EIGRP), the routing protocol will see the lost peer and should stop forwarding traffic (but as also noted by Giuseppe, this depends on the protocol timers), and/or, if supported by the platform, enable GRE tunnel keep alives (i.e. use the keepalive command on the tunnel interface - BTW, recall timers can also be adjusted for this command - one advantage of using keepalive, it takes the tunnel "DOWN", can be useful for SNMP polling).


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