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How do I Isolate the Source of Tunnel Flapping EIGRP


Hi there!


I am having issues with tunnels flapping across sites on our network, our network is airgapped and we use the customer's already in place network as our backbone to communicate across sites. I have combed left and right through everything I can think of and cannot locate any issues with how our network is setup. I have had the engineers who setup our network look over everything and verify it's good.


Is there a way I can prove that the issue is on their devices / network infrastructure causing these issues?


Note: I do not have access to their network and cannot check any devices, I have to rely on their technicians to tell me if something is messed up, and we are locked in the endless battle of "It's not me, it's you!"


The hello / hold time for these tunnels on our side is 1/3. 

3 Replies 3

Georg Pauwen
VIP Master VIP Master
VIP Master



what technical info (e.g. configs, log file entries) do you have ? A flapping tunnel is often caused by recursive routing. Can you provide a schematic drawing of the topology ?

Giuseppe Larosa
Hall of Fame Master Hall of Fame Master
Hall of Fame Master


as noted by Georg one potential cause for flapping of tunnels is recursive routing that happens when :

the tunnel destination address ( external address) is advertised within the tunnel .

You need to be very careful about this

Have a host  /32 static route for each tunnel destination using the offered  IP next-hop on the physical exit interface.

This can help.

Also try to use higher timers for tunnel keepalive.


Hope to help



We know very little about what is going on here. We are told that there are tunnels. But what kind of tunnels? Is it standard GRE? Is it GRE with IPSec? Is it an IPSec tunnel? Is it a VTI tunnel? Any detail you can provide may help us to better understand the issue.


We are told that there is flapping. Is it tunnel interfaces flapping? Is it EIGRP neighbor relationship flapping? Any detail you can provide may help us to better understand the issue.


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