GRE tunnel limit?

Answered Question
Mar 9th, 2010

Hello,

Is there a limit on the number of GRE tunnels that can be configured on a router?

Any advice welcomed.

Thanks

Phil

I have this problem too.
0 votes
Correct Answer by Richard Burts about 6 years 8 months ago

Phil

As Lei Tian points out there may be factors such as memory constraints that will place practical limits on how many tunnels you can support. But there is also a hard limit on the number of tunnels that you can configure. That limit is based on the limitation of the number of IDBs supported by your router. The IDB is the Interface Descriptor Block and each interface (physical, or tunnel, or loopback, or whatever) requires an IDB. The number of IDBs will vary by platform and sometimes by release level of the code that you are running. You can use the privileged command show idb to see what the limitation is on your router. On the 1841 router that I just checked the limit on IDB is 1200 (which is a pretty large number - I believe that you would encounter other limits on performance or on size of configuration before you exhaust the IDB limit).

HTH

Rick

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Lei Tian Tue, 03/09/2010 - 07:56

Hi Phil,

I think that is a question depends on platform and IOS version. It is better to test it to find the answer, and you might hit resource limitation other than the number of tunnels, like cpu, memory.

HTH,

Lei Tian

Correct Answer
Richard Burts Tue, 03/09/2010 - 13:54

Phil

As Lei Tian points out there may be factors such as memory constraints that will place practical limits on how many tunnels you can support. But there is also a hard limit on the number of tunnels that you can configure. That limit is based on the limitation of the number of IDBs supported by your router. The IDB is the Interface Descriptor Block and each interface (physical, or tunnel, or loopback, or whatever) requires an IDB. The number of IDBs will vary by platform and sometimes by release level of the code that you are running. You can use the privileged command show idb to see what the limitation is on your router. On the 1841 router that I just checked the limit on IDB is 1200 (which is a pretty large number - I believe that you would encounter other limits on performance or on size of configuration before you exhaust the IDB limit).

HTH

Rick

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