Debian can't load web page - Kubuntu can

Azizcoos · 12-30-2006, 03:45 PM

Quote:

echo 0 >/proc/sys/net/ipv4/tcp_window_scaling

That works here with konqueror on sid amd64. What does it do?

craigevil · 12-30-2006, 04:58 PM

Wtf? Using echo 0 >/proc/sys/net/ipv4/tcp_window_scaling and I can connect to the site.

With it on I can't even with firewall off and a direct connection to my cable modem. Weird.

Is that something that is in the kernel?
If it is , it might explain why I couldn't connect and others using "pure" Debian Sid could; since I am using a Sidux kernel 2.6.18.5-slh-up-1 and not a "vanilla" Debian kernel.

uselpa · 12-30-2006, 05:00 PM

The funny thing is, on Ubuntu this value is set to 1, not 0. Exactly as on my Slackware box. So it's probably not this value directly, but something linked to it.

uselpa · 12-30-2006, 05:48 PM

It appears to be an issue with TCP window scaling and broken routers. The scaling options have changed as of kernel 2.6.17 and the problem seems to occur if you have a lot of RAM and of course a broken network equipment between you and the server.

Setting back the values to those of an earlier kernel does the trick:

Code:

root@slackw:$ echo "4096 16384 131072" > /proc/sys/net/ipv4/tcp_wmem
root@slackw:$ echo "4096 87380 174760" > /proc/sys/net/ipv4/tcp_rmem

And I checked on Ubuntu, it has exactly those values which explains why it works.

Some reading on this issue.

rickh · 12-30-2006, 06:52 PM

From my 64-bit Debian, Kernel 2.6.18-3, 512MB RAM ... which handles the site fine:

Code:

debian64:~# cat /proc/sys/net/ipv4/tcp_wmem
4096    16384   1048576
debian64:~# cat /proc/sys/net/ipv4/tcp_rmem
4096    87380   1048576
debian64:~#

craigevil · 12-30-2006, 07:40 PM

cat /proc/sys/net/ipv4/tcp_wmem
4096 16384 2097152
cat /proc/sys/net/ipv4/tcp_rmem
4096 87380 2097152

Without using the echo 0 > /proc/sys/net/ipv4/tcp_window_scaling cant connect to the site. Using the 0 connects to the site almost instantly.

Did this and now it works without doing echo 0 > /proc/sys/net/ipv4/tcp_window_scaling

vi /etc/sysctl.conf

add the following two lines

net.ipv4.tcp_wmem = 4096 16384 131072
net.ipv4.tcp_rmem = 4096 87380 174760

sysctl -p

Which is basically the same thing uselpa said to do. So it does come down to something having to do with the kernel I take it?

Wonder what other sites I couldn't connect to that this might have fixed? Thanks for the information on how to fix this issue.

Azizcoos · 12-30-2006, 07:49 PM

Here's the info from my three afflicted systems:

Code:

uname -r
2.6.18-2-amd64
cat /proc/sys/net/ipv4/tcp_wmem
4096    16384   4194304
cat /proc/sys/net/ipv4/tcp_rmem
4096    87380   4194304

uname -r
2.6.18-3-686
cat /proc/sys/net/ipv4/tcp_wmem
4096    16384   262144
cat /proc/sys/net/ipv4/tcp_rmem
4096    87380   262144

uname -r
2.6.17-2-k7
cat /proc/sys/net/ipv4/tcp_wmem
4096    16384   524288
cat /proc/sys/net/ipv4/tcp_rmem
4096    87380   524288

After changing them as suggested, they all work!
So is this a kernel bug or what?