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brad_11440's avatar
brad_11440
Icon for Nimbostratus rankNimbostratus
Jan 15, 2009
Solved

FastL4 vs Optimized TCP Profiles

We run active/standby 6400 (platform D63a) LTM's for our production applications. They are accessed via clients on a private network with an average latency around 80ms. Nearly all of our virtual se...
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  • smp_86112's avatar
    smp_86112
    Jan 20, 2009
    Maybe it's about the right time to have you post your VIP config from the bigip.conf. It's possible you have other settings applied to the VIP which conflict with a FastL4 profile??? Also it might be helpful to paste the values of the TCP profile you have applied.

     

     

    Regarding the window size...the behavior you see was bothering me for a long time until it finally clicked in my brain. Yes, the TCP window size always starts at 4380. The trick is to understand whether the LTM is sending or receiving data. When the LTM is sending data, as in this case, there is no need for the LTM to increase its receive window - which is the parameter you refer to in the trace.

     

     

    When the LTM is receiving large amounts of data and you do a trace, you'll see that the LTM receive window starts out at 4380, and quickly increases to the value of the Receive Window as specified in the TCP profile that is applied.

     

     

    The LTM is smart - it starts out with a small window size so it does not need to allocate more memory than necessary for the TCP connection. If it needs to adjust the receive window (when it is receiving data), you'll see it go up.
JRahm's avatar
JRahm
Icon for Admin rankAdmin
Jan 15, 2009
If you're only decisive at layer 4 and below (and you don't need oneconnect), fastL4 is the way to go as it utilizes the Packet Velocity asic on your hardware (though only in assist mode in your case since you're using snat). If you want to optimize http in any way, you'll need the tcp+http profile combination. I've done this with the lan-optimized profile with 20000 connections/second at 300 Mbps traffic on a 3400 (single processor) and CPU never hit 15% and the memory utilization never climbed above 400MB. The 6400 is rated much much higher than that, so unless you are currently really pushing the box, you should be fine with the optimized profile. I would recommend the LAN optimized, even with the WAN environments, it has worked well for me and I've heard the same from other users that it performs better. Your mileage may vary, so test if you can, set up a vip in parallel that you can push X percentage of users to for piloting.