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 performance tests going via the LTM compared to straight to the server gives about the same result, but as the latency increases, speed doing via the LTM starts to fall below going straight to the server thru the firewall. One key difference that's shown up in packet captures - in the initial SYN+ACK the server sends back to the client, it shows the server supports TCP Window Scaling option, or WSOPT as it's abbreviated in Wireshark. I've been trying to figure out how to support this option on the F5, can't make it happen. TCP Window Scaling is part of RFC 1323 so it should be included in the default tcp profile, but I don't see it in the capture. Is anyone out there familiar with this option, and knowledgeable of the trick to making it work?

How do I enable the TCP Window Scaling option?

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.

JG
Cumulonimbus
Dec 13, 2014
Window Scaling is enabled in the default tcp profiles on F5. See "SOL7559: Overview of the TCP profile" ( https://support.f5.com/kb/en-us/solutions/public/7000/500/sol7559.html ).
John_Heyer_1508
Cirrostratus
Dec 13, 2014
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
  Cumulonimbus
  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.
nitass_89166
Noctilucent
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
  Cirrostratus
  Dec 13, 2014
  That's probably something to do with it. I had created a custom TCP profile in order to turn on Rate Pace (which significantly speed things up) and also set these per F5 recommendations: Proxy Buffer Low: 98304 bytes Proxy Buffer High: 131072 bytes Send and receive buffer are not changed though: Send Buffer: 65535 bytes Receive Window: 65535 bytes
- John_Heyer_1508
  Cirrostratus
  Dec 13, 2014
  Ahhh so I set "Send Buffer" and "Receive Window" to match the Proxy Buffer High, now WSOPT is showing up in the packet captures and speeds are actually surpassing hitting the server directly
- John_Heyer_1508
  Cirrostratus
  Dec 13, 2014
  This is 11.5.1 HF6 btw
nitass
Employee
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
  Cirrostratus
  Dec 13, 2014
  That's probably something to do with it. I had created a custom TCP profile in order to turn on Rate Pace (which significantly speed things up) and also set these per F5 recommendations: Proxy Buffer Low: 98304 bytes Proxy Buffer High: 131072 bytes Send and receive buffer are not changed though: Send Buffer: 65535 bytes Receive Window: 65535 bytes
- John_Heyer_1508
  Cirrostratus
  Dec 13, 2014
  Ahhh so I set "Send Buffer" and "Receive Window" to match the Proxy Buffer High, now WSOPT is showing up in the packet captures and speeds are actually surpassing hitting the server directly
- John_Heyer_1508
  Cirrostratus
  Dec 13, 2014
  This is 11.5.1 HF6 btw
Karthick1
Cirrus
Dec 18, 2019
@ John Heyer 150875 , Thanks it works ..