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New Member

TCP Tunning

Hi all

This is a very challenging question

1) How to tune WINT servers have gigabit ethernet to make use of the 1000Mbps providied to it...ther is something needs to be done on the TCP stack to improve the performance...normally if u have a WIN NT connected with a 100Mbps makes use os just 10% of that 100Mbps...but with WIN2K there is improvement in this...But since all of my servers are WIN NT can any one suggest the best way to tune my TCP STACK to utilize the gigabit ethernet speed..Please donttell me to change the server to WIN2K.

2)How can i compress my data & Header of a IP paket on cisco routers..Is it suggested to compress only the header ,data or both??

3) How can i do the same on Access Server say AS5300??

Honest suggestion & opinions are welcome...please send me if u have any convinient links for the above settings..

waiting for ur earliest reply

nagendr urs


Re: TCP Tunning


The most common approach to increase bw-utilization is to set the tcp window size to a higher value. This is a registry setting for which you can find detailed info (and warnings) on "Windows sets this to an appropriate value without user intervention." That is what Microsoft says but many people disagree.

In a WAN there is a formula to calculate the window size:

tcp window = 1.5 * bandwidth * round-trip delay / 8.

This is bw in bits/s and delay in seconds.


In todays high-speed networks the maximum setting (65536 bytes) is not large enough. Win2k and XP use an offset-mechanism that allows for a larger size.

Compression: Do not use it on lines with speeds over 256k, it will mostly slow you down. Use either ip tcp header-compression or PPP compression with one of the available algorithms.

This can be done on any IOS platform, including the AS5300.



New Member

Re: TCP Tunning

Leo Thanks for that

i quick connection...My network consists of ATM & FR ...and u suggested that...its better to do a header compressions & it is available on all cisco IOS platform..can u please suggest how and send me a link to do it..

And as u suggested do not use it on lines with speeds greater than 256 K ?? what do u mean by that ?? ru talking abt the dial in line??

Re: TCP Tunning

Do not attempt to use compression on ATM or Frame Relay, it is not useful.

With a fast connection, it is better NOT to use compression. Explanation: The required processing overhead takes more time than simply forwarding the packet. Therefore, compression only improves througput on lines up to 256kb. On a faster line, you may even lose performance.

I would advise you to use compression ONLY on dial-up lines and low speed leased lines. This is a sample dialer configuration:

interface Dialer9

description demo1

bandwidth 64

ip unnumbered Loopback1

no ip directed-broadcast

encapsulation ppp

ip tcp header-compression

no logging event link-status

dialer remote-name demo1

dialer idle-timeout 180

dialer enable-timeout 2

dialer string 0012345678

dialer pool 1

dialer-group 1

no cdp enable

ppp authentication chap

Using ip tcp header-compression gives a significant improvement on telnet sessions because they contain lots of small packets. In a small packet, the relative gain of compressing the tcp-header is large. With applications that use larger packet-sizes (> 256 bytes) you will gain more with normal ppp compression.

To activate this:

int ...

encapsulation ppp

compress stac

See your IOS command reference for detailed info.