ACE and MTU settings

Unanswered Question
Jun 6th, 2010

I'm running an ACE module in a CAT 6513.  we recently ran into the following issue:

We have organizations all across the country connecting to a server farm running MS SharePoint.  This server farm consists of 3 load balanced servers.

Some organizations couldnt open web pages and it appeared to be an issue with the size of the content.  Packet captures at the client side identified the "dont fragment" bit being set during the TCP/IP communication process.

Our thoughts were to use the path MTU settings and allow fragmenting on the servers to handle/adjust as necessary.  after making these adjustments, the problem persisted.  Only after hard coding the MTU settings on the servers to a value of 1360  did the problem resolve.

Of note.  Prior to making any change on the server side, we had some customers connect directly to the server(s) and it worked fine.

I suppose I'm not clear on what the ACE would be doing to cause this issue.  I have looked through the configuration and the only MTU settings are at the interface level and those are all set to 1500.  I guess i'm not clear on how MTU's affect the traffic as well...

Anybody that could provide any insights on this it would be appreciated.


I have this problem too.
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Gilles Dufour Mon, 06/07/2010 - 00:25

This is most probably a MSS issue (not MTU).

What software version ?

L7 rule or L4 rule ?

show np 1 me-stats "-snorm" ...any drop mss exceeded ?



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