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smp_86112's avatar
smp_86112
Icon for Cirrostratus rankCirrostratus
Aug 14, 2008

TCP Window Size on Forwarding (IP) Virtual Server

We recently found that our LTMs are significantly throttling application performance because the TCP window sizes on our default TCP profile are 8k.

 

 

Now I'm engaged in troubleshooting poor application response on another application whose server is accessed through a Forwarding (IP) Virtual Server. Not being very familiar with the specifics of forwarding virtual servers, I expected to see a protocol profile somewhere in the configuration where I could then adjust the window sizes. However it appears there is no such profile applied to this type of VS.

 

 

Does a Forwarding (IP) Virtual Server apply the TCP window sizes in the default TCP profile (or some other profile)? Or does it simply pass through the window size advertised by the client and the server? Looking at the FastL4 profile config, the TCP Window Scale Model is set at "Preserve" so I suspect that is precisely what is happening. Just looking for confirmation.

 

 

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  • dennypayne's avatar
    dennypayne
    Icon for Employee rankEmployee
    Aug 14, 2008
    I'm not sure if a forwarder uses default window sizing or not (would be a good support question) but you are correct that there is no way to manipulate the window sizing in a FastL4 profile other than changing the TCP Window Scale Model to "Strip" (which I'm not sure what good that would do). Interestingly on a 9.4.3 box I'm looking at the online help also says you can set it to "Rewrite" however that option is not actually available in the drop-down box. That may be a bug in the help or the GUI, not sure which. I'm thinking this definitely deserves a support case to clarify this.

     

     

    Denny