From: Lore <skizzo82@yahoo.com>
To: Henrik Nordstrom <hno@marasystems.com>
Cc: Netfilter Users <netfilter@lists.netfilter.org>
Subject: Re: libipq: problems changing destination port
Date: Mon, 31 Oct 2005 16:37:05 +0100 (CET) [thread overview]
Message-ID: <20051031153705.42467.qmail@web52803.mail.yahoo.com> (raw)
In-Reply-To: <Pine.LNX.4.61.0510292351550.15219@filer.marasystems.com>
First of all I have to apologize with Henrik because I
replied directly to him (I didn't noticed that Yahoo
replies only to the sender by default).
then it comes the repost:
Ok...
I do a new checksum... before changing the port I
checked that the checksum Algorithm was right by
comparing the system computed check with the one
computed by me.
Everything was right.
but in the moment I change the port the packet never
arrives.
Here's what comes out from TCPDump fetching on port
2026 the packets (originally for port 2022) that I
changed... from the first Ack on...:
root@morningmoon:/home/lore# tcpdump -i wlan0 dst port
2026 -vvv
tcpdump: listening on wlan0, link-type EN10MB
(Ethernet), capture size 96 bytes
16:27:50.094991 IP (tos 0x0, ttl 64, id 39743, offset
0, flags [DF], proto: TCP (6), length: 60)
192.168.0.4.32788 > geronte.cs.unibo.it.2026: S, cksum
0x5034 (correct), 2890202236:2890202236(0) win 5840
<mss 1460,sackOK,timestamp 14378819 0,nop,wscale 2>
16:27:50.119230 IP (tos 0x0, ttl 64, id 625, offset
0, flags [DF], proto: TCP (6), length: 40)
192.168.0.4.32788 > geronte.cs.unibo.it.2026: R, cksum
0x36fd (correct), 2890202237:2890202237(0) win 0
16:27:52.971108 IP (tos 0x0, ttl 64, id 39745, offset
0, flags [DF], proto: TCP (6), length: 60)
192.168.0.4.32788 > geronte.cs.unibo.it.2026: S, cksum
0x447b (correct), 2890202236:2890202236(0) win 5840
<mss 1460,sackOK,timestamp 14381820 0,nop,wscale 2>
16:27:52.995399 IP (tos 0x0, ttl 64, id 626, offset
0, flags [DF], proto: TCP (6), length: 40)
192.168.0.4.32788 > geronte.cs.unibo.it.2026: R, cksum
0x36fd (correct), 2890202237:2890202237(0) win 0
Any Idea?
Thanks a lot...
lore
--- Henrik Nordstrom <hno@marasystems.com> ha scritto:
> On Sat, 29 Oct 2005, Lore wrote:
>
> > and in the code I change the tcphdr->dest to 2021,
> do
> > a new checksum and verdict it with NF_ACCEPT.
> >
> > The packet get's silently dropped and I don't know
> > why...
>
> Should work.. but make sure you get the TCP header
> checksum correct...
>
> What does tcpdump say?
>
> Also beware that conntrack won't be too happy if you
> modify the
> "connection details" like this. If you need
> conntrack loaded such mangling
> of the packets is better left to NAT..
>
> Regards
> Henrik
>
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next prev parent reply other threads:[~2005-10-31 15:37 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-10-29 12:59 libipq: problems changing destination port Lore
2005-10-29 21:54 ` Henrik Nordstrom
2005-10-31 15:37 ` Lore [this message]
2005-10-31 16:35 ` Henrik Nordstrom
2005-10-31 19:27 ` Lore
2005-11-01 0:24 ` Henrik Nordstrom
2005-11-01 15:11 ` Martijn Lievaart
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