Michael wrote:
> Hi,
> I have installed new kernel 2.4.21, and now all my connections to the
> services that my broadband router runs by itself are refused - that is,
> I can not access www (web-based router/firewal administration) and lp
> (printer attached to the router) connections are refused. At the same
> time it works fine as the gateway to the WAN - I am able to browse the
> Internet. The router is USR8000, and I am running Debian 3.0 with a
> custom built kernel. Below is the output of the tcpdump with the old
> kernel, where everything works fine, and with the new kernel, where the
> connection to the 192.168.123.154/www is refused. Can someone advise me
> on what may be the reason?
>
> old kernel: 2.2.20-idepci
> tcpdump: listening on eth0
> 15:43:54.560040 192.168.123.149.1202 > 192.168.123.254.www: S
> 2279303454:2279303454(0) win 16060 > 0,nop,wscale 0> (DF)
> 15:43:54.561491 192.168.123.254.www > 192.168.123.149.1202: S
> 331674700:331674700(0) ack 2279303455 win 5840
> ....
> the connection is accepted
>
> new kernel 2.4.21-custom
> tcpdump: listening on eth0
> 15:27:03.527038 192.168.123.149.32786 > 192.168.123.254.www: SWE
> 4056883529:4056883529(0) win 5840 > 0,nop,wscale 0> (DF)
> 15:27:03.528470 192.168.123.254.www > 192.168.123.149.32786: R 0:0(0)
> ack 4056883530 win 5840
>
> the connection is refused.
>
> Thank you in advance,
> - Michael
>

Ok, got it. The explicit congestion notification flags (SWE) are not
supported by my router. Turned it off and it worked:
echo 0 >/proc/sys/net/ipv4/tcp_ecn

Thanks!