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Network connectivity problems w/default 2.6.8.1 sysctl settings



Starting last night I was unable to access Gmane via either NNTP or HTTP.
The TCP handshake succeeds, but nothing further happens. After a great deal
of troubleshooting (including about an hour on the phone with my ISP this
evening), I finally determined that the problem is with a sysctl setting
that changed somewhere between the 2.6.7 and 2.6.8.1 vanilla kernels.

The problem sysctl is net/ipv4/tcp_default_win_scale. On vanilla 2.6.7, this
defaults to 0. On vanilla 2.6.8.1, this defaults to 7. With it set to
anything higher than 4, I have problems with Gmane.

The kernel itself is not to blame, as I had no problems accessing Gmane from
this system before last night - it's probably an issue similar to that
sometimes seen with ECN turned on.

I don't know if this has been reported before (though I haven't seen
anything on this list), but I wanted to let people running recent 2.6
kernels know that, if they experience odd TCP networking issues (successful
handshake, but no data transfer), they should check this setting.

Adam



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