Buckets in Cisco Catalyst Switches

[cohen.moshe]

Hello,

My name is Moshe and I came across the following article from CiscoPress:

http://www.ciscopress.com/articles/article.asp?p=474239&seqNum=2

Going through the article, I found out about the issue of Buckets:

"

As previously mentioned, the CAM table has a limited size. Cisco Catalyst switches use the 63 bits of source (MAC, VLAN, and so on) and create a 14-bit hash value. If the value is the same, there are eight buckets in which to place CAM entries. These entries expire after a certain inactivity period. (The default on the Cisco Catalyst switch is 5 minutes.)

"

I was trying to find out more about the buckets - their usage, implementation and issues. Yet I could not find any other source of information regarding them.

Do those buckets really exist? Do they exist in all versions of Catalyst or only newer ones? How is the hash calculated?

Is there any more information available regarding them?

Thanks in advance,

Moshe

[Joseph W. Doherty]

Disclaimer

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.

Liability Disclaimer

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.

Posting

Do those buckets really exist? Do they exist in all versions of Catalyst or only newer ones? How is the hash calculated?
Is there any more information available regarding them?

Only Cisco could answer those questions.  You might find additional information searching Cisco's main website, especally reviewing technotes and white papers.

I was trying to find out more about the buckets - their usage, implementation and issues. Yet I could not find any other source of information regarding them.

"Buckets" is a term often associated with hashing and hash tables.  If you search for information using hashing as a search method, you'll likely also come across information about "buckets".  You might start with: http://en.wikipedia.org/wiki/Hash_table and http://en.wikipedia.org/wiki/Hash_function.

[cohen.moshe]

Thank you for your answer, JosephDoherty.

I know the general term "Buckets" from hashing tables and other places. What I am interested abuot is Cisco's implementation.

I agree with your saying:

Only Cisco could answer those questions. 

Yet I have not found relevant information on their sites. Is there another way you recommend for finding this information and/or contacting Cisco for questions regarding it?

Thanks again

[Joseph W. Doherty]

Disclaimer

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.

Liability Disclaimer

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.

Posting

If you have access to Cisco Networkers presentations, they sometimes have additional information there.

Or, if you have a reason why their implementation may impact your production network, you might be able to open a TAC case for clarification.

Lastly, if you're on really good terms with their sales support, and/or the answer is important as part of a buying decision, they might find out for you (possibly under NDA).

Otherwise, as this is most likely consider proprietary information, they might be unwilling to share this information.

PS:

Oh, if you're writing a book that will be published under Cisco Press, they might provide information you would otherwise be unable to obtain.