network problem after yum update

Hi, I just did a yum update (about 600 MB) to kernel 2.6.17-1.2139_FC5
I can browse some websites but not others (no reply e.g. from www.linuxquestions.org I am contacting you through my second FC3 PC).
So I had a look with ethereal and saw that some packages sent by my system have a checksum error (GET / HTTP/1.1). But this happens for both, the sites that reply and the ones that don't.
I also noticed before the update some such checksum errors.
I don't know if they have anything to do with the problem.

yum update, ssh, mail download also don't work anymore, no reply.
I am stuck for the moment. What can I do?

Thanks
Ernst

More:
ping still works for all sites.
ssh works on LAN but not external net.
Disabling Firewall and SELinux did not help.

My second PC (FC3) also sends out http requests with checksum errors, yet web browsing works well! Maybe this is not the cause of the trouble.
The troubled PC uses FC5 64-bit.

Workaround: I boot with the older kernel-2.6.16-1.2111_FC5 and all is fine.
Still no idea what is wrong with kernel-2.6.17-1.2139_FC5

(added to messge #1. Sorry can't delete this one)

Ernst:

I am seeing the same problem after updating to the 2.6.17-1.2174_FC5 kernel via YUM. An Ethereal sniffer trace shows several "TCP Previous Segment Lost" error packets, also "TCP Window Updates", and "TCP Retransmissions" for HTTP traffic to/from the internet and I'm even getting these errors on intranet FTP traffic between my two PC's on the same subnet.

The workaround is the same as yours, boot with the original FC5 kernel (2.6.15-1.2174_FC5). Sounds like somebody broke the TCP/IP stack in 2.6.17-1.2174.

Evan Wheeler

The solution is to disable tcp window scaling. As root, execute this command.

sysctl -w net.ipv4.tcp_window_scaling=0

Then retry your failing connections.

Many thanks to jcliburn for your help.

Wishing to know some background I did a search on 'tcp window scaling' and found http://lwn.net/Articles/92727
which satisfied my curiosity.