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New Member

TCP Window Size


When downloading files from a server that connects via an SSL connetion terminated on CSS, we're seeing very slow download time. When we bypass the CSS and terminate the SSL connection directly on the server, downloads are approx. 5X faster.

The server has a TCP window size of 65535, can TCP windows be adjusted on a CSS for that particular service or content rule. What's the default TCP window size ?




Re: TCP Window Size

By default, the CSS sends a client-side or server-side TCP window size of 12,288 bytes

More details at

Syed Iftekhar Ahmed

New Member

Re: TCP Window Size

Hi Syed,

Thanks for the link, it was very helpful...

One more thing, this is a snapshot of my SSL Proxy List config, can you let me know if you think it'll work. Especaially the TCP window size commands, does the order/placement matter here ?

ssl-proxy-list SSL1

ssl-server 1

ssl-server 1 rsakey INFO-test

ssl-server 1 rsacert INFO-test

ssl-server 1 vip address

ssl-server 1 cipher rsa-with-rc4-128-md5 88

ssl-server 1 tcp server window 40960

ssl-server 2

ssl-server 2 vip address

ssl-server 2 cipher rsa-with-rc4-128-md5 88

ssl-server 2 rsakey INFO-test-admin

ssl-server 2 rsacert INFO-test-admin

ssl-server 2 tcp server window 40960

ssl-server 1 urlrewrite 1 *

ssl-server 2 urlrewrite 2 *

ssl-server 1 ssl-queue-delay 0

ssl-server 2 ssl-queue-delay 0

ssl-server 1 tcp virtual nagle disable

ssl-server 2 tcp virtual nagle disable

ssl-server 3

ssl-server 3 rsakey INFO-test-su

ssl-server 3 rsacert INFO-test-su

ssl-server 3 vip address

ssl-server 3 cipher rsa-with-rc4-128-md5 88

ssl-server 3 urlrewrite 3 *

ssl-server 3 ssl-queue-delay 0

ssl-server 3 tcp virtual nagle disable

ssl-server 3 tcp server window 40960


Re: TCP Window Size

Use the following lines in your ssl services.

ssl-server <#> tcp server window 40960

ssl-server <#> tcp virtual window 40960

If it doesnt improve performance

try disabling the Nagle algorithm and setting the SSL Ack delay to


ssl-server 10 tcp virtual nagle disable

ssl-server 10 ssl-queue-delay 0


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