cannot access a site with kernel 2.6.7 or 2.6.8, 2.6.6 is ok

[Daniel Lawson]

>Only the 2.6.6 will access http://www.carsdirect.com/
>The other two will just hang.
>I used the same config file for each with a 'make oldconfig'
>
>I tried Firefox 0.9.1, 
>Konqueror 3.2.2-4 (kde 3.2.2-6 Red Hat),
>and Mozilla (no version available while running Firefox).
>
>I thought the site was down but accessed it from XP using Firefox 0.9.1
>Then I rebooted to the lowest kernel and it worked in Linux.
>
>
>What in the kernel could posibly cause this with only this site?
>  
>

Having ECN enabled can cause this. Some routers see the ECN bit and for 
some unknown reason, drop packets with them enabled on the floor.

cat /proc/sys/net/ipv4/tcp_ecn

If the result is 1, you have ECN enabled. If it's 0, you don't, and 
there is some other problem. Some routers drop packets with TOS bits 
enabled, but thats more likely to be a firewall-related issue (ie, your 
forwarding path enables TOS)

If you have ECN enabled, you can disable it by doing

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

as root. You can also set

net.ipv4.tcp_ecn=0

in /etc/sysctl.conf (not sure if this is correct for FC2, it's the 
standard place however) To have this fix applied automatically.


see http://www.wlug.org.nz/ECN for some more information.




-- 
Daniel Lawson
WAND Group, Computer Science Department
University of Waikato
email: daniel at wand.net.nz 	phone: +64 7 838 4466  ext 6254