Re: ipt_unclean: TCP flags bad: 4

Luigi Genoni (kernel@Expansa.sns.it)
Sun, 22 Jul 2001 19:51:43 +0200 (CEST)


There was a bug introduced with kernel 2.4.6, but it was
solved with one of the latest 2.4.7-pre patch, i do not remember which
one.

actually i was happily using tcp_unclean on my production servers, but
with 2.4.6 i was forced to avoid it.
I still have to try 2.4.7 to see if it works properly.

If you use a rule like

iptables -A INPUT -m unlean -j DROP

are you still able to connect in/out of your box?

bests
Luigi

On Sun, 22 Jul 2001, Alan J. Wylie wrote:

>
> I've just upgraded to 2.4.7, and I'm getting lots of errors:
>
> ipt_unclean: TCP flags bad: 4
>
> I only see them when my ppp link is up - pppd version 2.4.0
>
> Looking at ipt_unclean.c it seems that this message will be generated
> when I send a packet with flags set to RST only.
>
> I've run a ppp session with the pppd option "record" turned on, and
> analysed the output with "ethereal". This is indeed what is on the
> wire. I'm no expert on TCP I'm afraid. The complete TCP stream
> follows:
>
> ------------------------------------------------------------------------------
> No. Time Source Destination Protocol Info
>
> 129 12.800000 62.137.113.223 news.svr.pol.co.uk TCP
> 1148 > nntp [SYN] Seq=3684831495 Ack=0 Win=5840 Len=0
>
> 131 12.900000 news.svr.pol.co.uk 62.137.113.223 TCP
> nntp > 1148 [SYN, ACK] Seq=2607886663 Ack=3684831496 Win=32736 Len=0
>
> 137 13.300000 62.137.113.223 news.svr.pol.co.uk TCP
> 1148 > nntp [FIN, ACK] Seq=3684831502 Ack=2607887466 Win=7090 Len=0
>
> 142 13.400000 62.137.113.223 news.svr.pol.co.uk TCP
> 1148 > nntp [RST] Seq=3684831503 Ack=0 Win=0 Len=0
> ------------------------------------------------------------------------------
>
> --
> Alan J. Wylie http://www.glaramara.freeserve.co.uk/
> "Perfection [in design] is achieved not when there is nothing left to add,
> but rather when there is nothing left to take away."
> Antoine de Saint-Exupery
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