I hope someone can tell me what's going on woth this problem:

I have a mandrake 10.1 system, connected via a US Robotics router to a cable modem. I also have two windoze pcs on the same router. All machines have a 100mbit/sec NIC installed, all are MSI athlon based boards, less than 12 months old. All machines use DHCP, but the router is configured to always give the same ip (192.168.123.100) to the linux machine, and port 80 is forwarded to that ip.

When surfing the net on the linux machine, most sites work just fine but just occasionally, I come across one that is really, really really slow. Now for the bizzare bit... going to that same site on the windoze machine, hooked up by the same router - the site comes up just perfect.

One example is www.monkeybuttons.com - a site my wife uses for her quilting. wget shows a transfer rate of 31 bytes per second!! (yes, bytes!) but on the windoze machines, it comes up instantly. I also experienced the same at sun.java.com when trying to download the JVM for linux, I was getting transfer speeds of less than 1k/sec wheras on windoze, I get the expected 80k/sec

I've checked that the network config on linux is ok, it's got the right gateway and dns settings, in fact wget on the monkeybuttons site shows the ip is resolving just fine, I just get a chronically bad download speed.

I've stopped almost all the services on the linux (nfs/samba/sshd etc) and checked that it's not configured to use any sort of proxy server. I even did a fresh install of mandrake and still I have the problem.

I've also ttried turning off all port forwarding at the router, and also tried placing the linux server in the DMZ.

I'm no newbie but this has got me totally confused! I can't even begin to think what the issue may be here. How can just the odd few sites be very very slow on one machine but not on others on the same network???

Can any networkin gurus help me here? PLEASE????!!!

Yeah.. that problem drove me NUTS !

asuming you have the same problem as me ofcourse.

Some 2.6.x linux kernels have a tweaked tcp window size that in theory should allow for a more efficiant network.

and id did... however some time after this tweak was introduced to the kernel tree, it was discovered that some MS windows firewall's and some Routers were broken, and simply refused to forward these tcp packets.

The sites that are running slow are the sites that have such broken firewall's on route between the server, and your computer.

there are 2 fixes that i know of.

1: use a sysctl system call to change the tcp window size back to default. (this can also be done with the /proc interface)

im sorry i cant remember the exact command, but atleast im pointing you in the right direction.. its been mentioned a few times on this site, search for things like "sysctl tcp window size broken firewalls slow internet"

2: upgrade to the latest kernel, i think the tweak was removed after it was realied how much broken hardware there is out there.

hope this helps.

THANKYOU THANKYOU THANKYOU!!!!!!!!!!!!!!!!!!!!

You most certainly pointed me in the right direction, you gave the wrong parameter but othwerwise described the problem and was easily able to track down the fix.

If I ever win the lottery you can have half the winnings!!!!!

It's the tcp window scaling that some routers don't like...

I didn't find it here but there's a good page that explains it and I'll paste the relevant commands here for others to find in the future...

I hope it's ok to quote a para from another website, if not I'm sorry...
This is from lwn.net at http://lwn.net/Articles/92727/

"In the mean time, anybody running a current kernel who is having trouble connecting to a needed site can work around the problem with a command like:


echo 0 > /proc/sys/net/ipv4/tcp_default_win_scale
or by adding a line like:


net.ipv4.tcp_default_win_scale = 0
to /etc/sysctl.conf.
"

Now I gotta spend a few hours setting up my brand new installation again. duh. Oh well, it's all good learning!

oops..
glad to hear i could help anyways.

wow, half a lottery win.. sounds like you were REALLY struggling withthis one, ill keep my fingers crossed for you, lol.