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Community Member

Fixing flapping tunnels

Hi, I have quite a large VTI network with three headends. At times the spokes start to flap one or two of their tunnels to the headends and this continues until I manually shut down the interface and bring it back up.

Is there a way I can automate this procedure? I was thinking about IP Event Dampening but this does not shut the interface down so the issue will continue. I was also thinking about an EEM applet but am not too experienced with EEM and my attempts so far have not resolved the issue.

Does anyone have any suggestions?


Re: Fixing flapping tunnels

Try to lower the MTU of the GRE tunnel from 1436 to 1400 on both sides

Re: Fixing flapping tunnels

Do you get any useful messages with the flap?

Kevin Dorrell


Community Member

Re: Fixing flapping tunnels

Hi, thanks for the replies.

In regards to the GRE comment, I should have mentioned earlier we are using VTI. Also, I do not think it would be an MTU issue as the issue occurs rarely (about twice a week, most times it is a different site) and we have over 130 sites setup. It is not a massive issue but it would be good if we could fix it.

And nope, no useful error messages. It just says the interface goes down then it comes up a few seconds later then goes down & continues to flap in that fashion until someone manually shuts the interface down and brings it back up.

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