Arch Linux

Breakage

Member

From: London

Registered: 2008-02-12

Posts: 198

Website

Slow internet speed because of RWIN and MTU

I've got a problem with cable modem "DHCP" speed the default internet settings for arch are very slow for me on a 2mb connection, I get 1700kbps max where as on other distros and windows i'm getting 1960+kbps the issue is RWIN size and MTU size.

With the default settings my RWIN is "128960" when it should be set to "51100" for my speed, also MTU is 576 which is very low (dialup MTU speed I think) for a cable modem which should be "1500".

I've tried setting my RWIN size in /etc/sysctl.conf like this in arch:

# Tweaks for faster broadband...
net.core.rmem_default = 51100
net.core.rmem_max = 51100
net.core.wmem_default = 51100
net.core.wmem_max = 51100
net.ipv4.tcp_wmem = 51100 51100 51100
net.ipv4.tcp_rmem = 51100 51100 51100
net.ipv4.tcp_mem = 51100 51100 51100
net.ipv4.tcp_rfc1337 = 1
net.ipv4.ip_no_pmtu_disc = 0
net.ipv4.tcp_sack = 1
net.ipv4.tcp_fack = 1
net.ipv4.tcp_window_scaling = 0
net.ipv4.tcp_timestamps = 0
net.ipv4.tcp_ecn = 0
net.ipv4.route.flush = 1

With extra tweaks for window scaling 0, timestamps 0 etc.. and done "sudo sysctrl -p" to set it.

But after retesting my settings at dslreports.com I get a very low RWIN like "9654" for some reason, does anyone know how to permanently set it to "51100" ?

I also have a problem with settings MTU I done "sudo ifconfig eth0 mtu 1500" that works fine but gets reset on reboot, I've looked though this thread http://ubuntuforums.org/showthread.php?t=82093 and it needs to be set in "/etc/network/interfaces" but I have no such directory.

So anyone know how to Permanently RWIN MTU for a DHCP network in arch?

EDIT: I've managed to set MTU to 1500 on boot now speeds are up to 1958kbps, now just wondering about RWIN

Last edited by Breakage (2008-02-24 05:33:52)

gorn

Member

Registered: 2008-02-01

Posts: 56

Re: Slow internet speed because of RWIN and MTU

You probably want tcp_window_scaling = 1, not 0.

Window scaling is used to let you have a bigger window size. The only reason to turn it off is if you are behind a router that distorts your TCP packets and causes connection issues. There is such a router between my school and the internet, and so I have my network script shut off tcp_window_scaling when connecting to the wireless at school. But I keep it on elsewhere.

Try turning it on and giving it a go.

Breakage

Member

From: London

Registered: 2008-02-12

Posts: 198

Website

Re: Slow internet speed because of RWIN and MTU

Thanks for the tip gorn and sorry for the late reply, will try it out.

javonera

Member

Registered: 2007-05-28

Posts: 16

Re: Slow internet speed because of RWIN and MTU

Breakage, how did you managed to set MTU at boot? I was just searching how to do it