Hello,
the man page of iptables says:
TCPMSS
This target allows to alter the MSS value of TCP SYN packets, to
control the maximum size for that connection (usually limiting it to
your outgoing inter-
face's MTU minus 40 for IPv4 or 60 for IPv6, respectively).
Of course, it can only be used in conjunction with -p tcp. It is only
valid in the mangle
table.
but when i put a TCPMSS rule into the filter table:
eris:~# iptables -I FORWARD -o eth2 -p tcp --syn -j TCPMSS --set-mss 1440
it shows up inserted:
eris:~# iptables -vnL FORWARD
Chain FORWARD (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source
destination
2 104 TCPMSS tcp -- * eth2 0.0.0.0/0
0.0.0.0/0 tcp flags:0x17/0x02 TCPMSS set 1440
10758 6553K ACCEPT all -- * * 0.0.0.0/0
0.0.0.0/0 state ESTABLISHED
0 0 GLOBAL_INVALID_STATE all -- * *
0.0.0.0/0 0.0.0.0/0 state INVALID
341 17732 BAD_TCP_PACKETS tcp -- * *
0.0.0.0/0 0.0.0.0/0
0 0 eth2_to_eth1 all -- eth2 eth1 0.0.0.0/0
0.0.0.0/0
341 17732 eth1_to_eth2 all -- eth1 eth2 0.0.0.0/0
0.0.0.0/0
0 0 ACCEPT all -- * * 0.0.0.0/0
0.0.0.0/0 state RELATED
0 0 LOG all -- * * 0.0.0.0/0
0.0.0.0/0 limit: avg 1/sec burst 3 LOG flags 0 level 6 prefix
`IPT_DROP_FORWARD '
eris:~#
and it actually seems to work:
eris:~# tshark -n -i eth2 tcp port 80
273.366753 62.178.111.127 -> 193.99.144.85 TCP 1989 > 80 [SYN] Seq=0
Len=0 MSS=1440 WS=0
So is the man page wrong?
From what i know from the netfilter concept, packet alteration should
be done in the mangle table, so the man page is right from theory, but
practically the target extension does not care?
eris:~# uname -a
Linux eris 2.6.24-etchnhalf.1-686 #1 SMP Sat Aug 15 16:51:49 UTC 2009
i686 GNU/Linux
eris:~# iptables --version
iptables v1.4.5
Thank you for clarification,
regards
Mart
--
To unsubscribe from this list: send the line "unsubscribe netfilter" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
