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New Member

buffer utilization

This may or may not be the right place to ask, but here goes anyway. As far as the Ciscos buffers are concerned, what types of information gets stored in what type of buffer. For example, I would expect a very large routing table...such as a BGP routing table would be stored in "huge" buffers.

So what types of information get stored in Huge, Large, Big, Medium and Small buffers?

Any info is greatly appreciated.

Martin Weddle - ADP Dealer Services

New Member

Re: buffer utilization


Packets going through the router get stored in buffers. i.e. small packet, small buffer, large packet - large buffer.

The BGP routing table would be help in main memory.

New Member

Re: buffer utilization

That helps....but there are still alot of things that are unanswered. The MTU for most protocols within a cisco router is 1500 bytes..A big buffer is 1536 bytes. So what about VeryBig, Large and Huge buffers? From what I can gather, all of these buffers are derived from main memory. I can see a 4096 byte frame relay packet going to a very big buffer.

I think things like an ARP cache would be dependent on how large the cache is. That would determine which type of buffer it resides in. What about dynamic NAT translations? Where might those actually reside? Probably dependent on the number of translations?

Thank you for the information...and thanks to anyone else who chooses to's very much appreciated.

Martin W.


Re: buffer utilization

Nothing other than packets are ever stored in buffers. Pick up Inside Cisco IOS Software (sheless plug) since it explains them very well. Or come to Networkers, and sign up for the architecture power session (another shameless plug). All of these other structures you talk about are stored in heap memory. The reason there are so many buffer sizes is because there are so many possible MTUs. You will find there is one buffer size just about every MTU possible. As for the size difference, remember that thing about birthdays and one to grow on? That extra space is for packet headers to grow in. Finally, huge buffers are spcifically used to reassembling packets which need to be reassembled--for istance, to be received by the router, or to terminate a tunnel.

Hope that helps.



New Member

Re: buffer utilization

Thank You! This answers all my questions. Thanks again to all who have contributed.

Martin W.

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