CSM is stripping tcp options when stickyness is configured

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Jul 15th, 2009
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I've found, what i think is a bug, in our CSM and want to share, and hopefully you've something to add (or solve?)

cisco CSM software 4.2.11 on a 6509 chassis, software 12.2.18 SXF15a

When configured a VIP with either ssl stickiness or regular stickiness, i noticed that the CSM is stripping all tcp options (except mss) in the first tcp/ip syn packet.

so, loosing tcp options like: Selective ACK, window scaling, tcp timestamps, which are the basics of high performance TCP/IP.

Without stickness, the tcp options are not touched.

Does anyone recognize this phenomena ?

Any Idea's?

PS: i noticed this after a complaint of a very slow website hosted by us in combination of some packetloss at the client.


Arjan Filius

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David Coupez Wed, 07/15/2009 - 07:12
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Few months ago, I had a similar problem. After weeks of investigation, it occured the problem was caused by a defect network adapter driver.

Is this problem always occur on all hosted servers?

siennax Wed, 07/15/2009 - 21:52
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Thanks for your reaction and questions.

I took only some "random samples" and noticed the difference (finally after "some hours" that:

-Sticki configured VIP/serverfarm, accessed on the VIP will strip all tcp options.

-accessing the real servers not.

as it concerns (in hour case) all same NIC's, NIC/server/client issues are excluded.

In our case there is no other device involved (with the two cases, via VIP and direct to real) othere then die CSM itself.


Arjan Filius

PS: i'm a month on holiday after today, a colleague will attend this thread.


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