How many numbers of GRE Tunnels are supported on Cisco 3925 router?

[manjong lim]

Hi...

I would like to know that.......

How many numbers of GRE Tunnels are supported on Cisco 3925 router?

Thanks....

[Joseph W. Doherty]

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Posting

Lots. 

Are you asking about absolute maximum number of tunnels, or how many can the 3925 support effectively?

If the former, would have to research the limitation, but likely it's from hundreds to thousands.

If the latter, depends much on volume of traffic crossing the tunnels and whether you need to fragment packets.

[Richard Burts]

Joseph points in the right direction in answering this question. The only hard limit on the number of GRE tunnels supported is the limit on the number of Interface Descriptor Blocks. Every interface (every physical interface and every virtual interface like GRE) requires an IDB and every platform has a limit on how many IDBs are supported on that platform. There is a show command to see how many IDBs are supported on your router if you want to find the number. But it is a fairly large number.

The real limit is the processing power required for the tunnels and this depends on how you will use the tunnels (is it a simple GRE tunnel or does the tunnel also use IPSec for encryption, will it just pass data traffic or will you run a routing protocol over the tunnel). But as Joseph says this is a pretty large number. How many GRE tunnels are you thinking of running on this router?

As one data point I have run routers will over 400 GRE tunnels (and using encryption) without any problem.

HTH

Rick