Red Hat Bugzilla – Bug 217063
Fails to access http://www.itu.int - possible TCP issue
Last modified: 2007-11-30 17:11:49 EST
Description of problem:
Access to http://www.itu.int is impossible.
Not only from a browser (firefox), but also from more basic methods
telnet www.itu.int 80
Either way, the transfer starts, but rapidly comes to a crawl.
One could say the problem should be reported to the site admin, but because
there is no problem accessing this site from a WindowsXP machine they probably
wont be very responsive :)
Note that it works with the "telnet" method on WindowsXP so there is nothing
specific to the browser itself.
Also note that the WindowsXP machine from which I can access this site
successfully is on the same network (hence going through the very same
router/firewall) as the linux machines from which I observe the failure.
Bottom line, it looks like a TCP issue specific to linux and this Web site. (I
have the same result with various flavours of linux - Ubuntu, Knoppix, FC4.)
Created attachment 142015 [details]
tcpdump while doing "telnet www.itu.int 80" from a FC6 host
Can be examined with "tcpdump -nnv -r <filename>
This attachement show the bug (look at the timestamps).
Created attachment 142018 [details]
tcpdump while doing "telnet www.itu.int 80" from a WindowsXP host
Can be view with "tcpdump -nnv -r <filename>.
This one show a transfer that works diligently.
I have noticed two differences between the two tcpdump's provided above.
1. the ack sent from FC6 are tagged "tox 0x10" while they are tagged "tox 0x0"
I have forced a "tos 0x0" with the following
iptables -A OUTPUT -t mangle -p tcp --dport 80 -j TOS --set-tos 0x0
2. in those same ack packets, I see the "win" value much smaller from FC6 than
I did not find a way to force that to a higher value.
3. I have taken a tcpdump while doing a http transfer from another site. It
shows the same behaviour as the one that fails from www.itu.int on FC6. i.e.
"tos 0x10" and small "win" value. But the transfer works just fine.
*** This bug has been marked as a duplicate of 207373 ***