Forum Discussion

John_Heyer_1508's avatar
John_Heyer_1508
Icon for Cirrostratus rankCirrostratus
Dec 13, 2014

How do I enable the TCP Window Scaling option?

I've been doing some performance tests uploading and download large files over SSL with an F5 LTM in the middle. The virtual server setup is standard, using the default tcp profile.   In most per...
application delivery
deployment
LTM
performance
TMSH
  • nitass_89166's avatar
    nitass_89166
    Dec 13, 2014

    what version are you running? have you tried to increase send/receive buffer e.g. 65536 bytes?

    Note: Beginning in 11.4.0, the window scale functionality is built into the TCP profile and cannot be manually disabled or enabled; it will be negotiated if the send or receive buffer is larger than 65535 bytes.

    sol7559: Overview of the TCP profile

    https://support.f5.com/kb/en-us/solutions/public/7000/500/sol7559.html
John_Heyer_1508's avatar
John_Heyer_1508
Icon for Cirrostratus rankCirrostratus

That's certainly my understanding, but the packet captures don't lie, and I don't see it in the syn+ack coming back from the F5.

 

Direct from the server, it's clearly there:

 

 

JG's avatar
JG
Icon for Cumulonimbus rankCumulonimbus
Dec 13, 2014
You can run tcpdump on the backend app server to see what tcp options F5 advertises; and you can also run it on the end-user side.