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Amartya_Ghosh_1's avatar
Amartya_Ghosh_1
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Mar 10, 2014

TCP Window Scaling in F5 LTM 11.2

We are observing some weird behaviour on the traffic passing through LTM in one of our setup. While analyzing TCP captures we identified LTM is disabling windows scaling ( Negotiated scale factor 0x0 ). We have taken multiple captures and final observation was that LTM recieves the packet with Win=8192 ( Negotiating scale factor 0x8 ) but packets leaving the LTM has Negotiated scale factor 0x0.

 

I have already verified the RFC1323 extension "Extensions for High Performance" is enabled in the TCP profile and even implemented LAN/WAN optimised profiles but do not see any difference in the traffic behaviour.

 

Setup: Remote server<--->FW<--->F5 (LTM)<--->Node

 

Anyone have idea or inputs on this ??

 

application delivery
deployment
LTM
microsoft
performance

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  • boneyard's avatar
    boneyard
    Icon for MVP rankMVP
    Mar 11, 2014

    your layout seems to have gone, could you redo it?

     

    anyway window scaling is a two sided deal i believe, both sides must want to do it. when you try to reach your end point without the bigip in between, is window scaling working then?

     

    also for better understanding can you output the virtual server config (cli) and the tcp profiles?

     

  • boneyard's avatar
    boneyard
    Icon for MVP rankMVP
    Mar 16, 2014

    sorry it took a little longer. it has been a while since i worked with this so i had to configure it to see how it worked.

     

    it is the Send Buffer / Receive Buffer that "enables" window scaling. remember the bigip is a full proxy (at least on your standard virtual servers), so if its buffers are only 64k max then window scaling is not needed. so if you increase them the bigip will start doing window scaling to enable these larger buffers.

     

    tcp-wan-optimized / tcp-lan-optimized play with different settings, but not with the actual Send / Receive buffer, so using them isnt enough.