CSM Cookie Limitation

[AaronKwok]

Hi I have successfully implemented the CSM for some time already. However I have encounter some problem when my user try to access certain webpages on the web server. The web page just not able load via the browsers.

I have verfiy that it is not a brower issue and it is certainly not the web server also. As I am able to access the web pages if I access the server directly instead via the CSM.

It's seem like that web pages that caus e the issue have cookie enable and if the cookie size exceed 1470 bytes the page will not be able load on my brower if I access via the CSM.

Does the CSM have such limitation or bugs or anybody have encouter such issue before. Pls advise as I could not find anything on Cisco web site. Thanks

[Gilles Dufour]

are you doing cookie stickyness ?

If so there is a parse-length parameter that limits the size of the buffer used to store the HTTP request in order to look for the cookie.

So, you should try to set this value to its maximum which is 4000.

If this size is not enough, you need to increase the variable 'MAX_PARSE_LEN_MULTIPLIER' from 1 to 2 or higher.

You can verify if this is the problem with the following command

'sho mod csm x tech proc 4' and look for the following counter

LB Rjct: L7 max parse len 0

If this is not zero the solution is what I just described.

Regards,

Gilles.

Thanks for rating

[AaronKwok]

Hi Gilles,

Thanks for the reply. However I'm not performing cookie stickyness on my csm. Currently I'm using stickyness via source IP.

The cookie on the web pages is to facilitate other function for the users. It serve as a way for user browsing the web pages to remember which check box or option they choose.

If more check boxes is selected on the web pages, the cookie value return to the user increase too. Thus the problem occur once it exceed 1470.

[Gilles Dufour]

Aaron,

if the CSM is not inspecting the HTTP traffic, it just passes the traffic to/from the server and only performs nating of ip addresses and ports.

So, if you're not using cookie stickyness are you using any other form of HTTP inspection ?

For example, do you have a url map ?

I think it would be easier if you could send your config and if possible try to capture a sniffer trace of the problem.

The CSM is being used by many people with cookie sizes much bigger than what you describe and there is no issue.

Is the traffic being fragmented maybe ???

What CSM version do you have ?

I would strongly recommend a sniffer trace on client and server sides.

Regards,

Gilles.

[AaronKwok]

No I'm not using any other form of HTTP inspection.

Btw I have did a trace before and have found out the HTTP GET did not go through when my client try to request for the page. This only occur when the server try to return the request with cookie value exceeding as mention above.

I can confirm the traffic is not Fragmented and the version I am using is 4.2.2

In any case tonight I will try to amend the default value of the CSM as recommended as I suspect and agree to a certain extent that the CSM should be able to handle cookie size much bigger than this. Will keep you posted. Thanks

[Gilles Dufour]

Aaron,

just one additional remark.

If you're not doing any http inspection, the CSM is not even aware there is a cookie.

For the CSM the traffic is simply TCP data.

So the problem must be somewhere else.

If possible capture a trace of the CSM portchannel and attach it to this post or send it to me directly at gdufour@cisco.com

Thanks,

Gilles.

[AaronKwok]

Hi Gilles,

Apparently after changing the buffer as suggest it manage to resolve the problem. Now cookie size more than 4000 on the webpage are able to load without any problem. Some how even though the CSM is not performing any http inspection, I believe the CSM still need to process the cookie in one ways or another. Any possible explanation. Thanks

[Gilles Dufour]

then you must be doing some sort of http inspection.

Send the config and I'll let you know what it is.

Do you have 'persisten rebalance' ?

Gilles.