02-21-2013 04:21 PM - edited 03-04-2019 07:06 PM
Is there a recommended number of GRE tunnels that Cisco 2921 ISR router with default configuration (512MB DDR2 ECC DRAM) can support?
02-21-2013 04:33 PM
Not really but your bandwidth will play a significant role.
02-21-2013 06:02 PM
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Posting
I agree with Leo, bandwidth usage is generally much more important then number of GRE tunnels. Additionally, percentage of traffic that will need fragmentation.
02-21-2013 10:08 PM
I happened to find this link regarding Interface Descriptor Block (IDB).
It states each physical interface on the router consumes a minimum of two IDBs:
One HWIDB for the physical port
One SWIDB for the Layer 2 encapsulation
Does this translate to the maximum of GRE and other Layer 2 encapsulations the router could support?
I'm not sure the maximum number of IDBs the router could support on a particular IOS is based on the default memory installed or maximum memory installed?
02-21-2013 10:16 PM
Does this translate to the maximum of GRE and other Layer 2 encapsulations the router could support?
Tan Han,
Please read my first post and Joseph's post.
02-22-2013 02:38 AM
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The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
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In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
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Does this translate to the maximum of GRE and other Layer 2 encapsulations the router could support?
More or less, yes. But not just L2 encapsulations, maximum number of interfaces.
I'm not sure the maximum number of IDBs the router could support on a particular IOS is based on the default memory installed or maximum memory installed?
Should be maximum amount of memory too.
However, Cisco recommends a 2921 for up to 50 Mbps of WAN bandwidth. So if you did have about 1,400 GRE tunnels, that's about 36 Kbps each, about half a DS0. Normally, you'll run out of CPU performance before hitting the limit of how many tunnels you can define.
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