Hi, this is my first post to this list. I have tried goggling, but I have
failed, and i think now it's time to ask for help.
I am running a firewall with Debian Linux (kernel 2.6.15) and am I am
expriencing a strange behavior in a simple SNAT rule.
I was running a dual gateway equal cost multipath configuration, but I
have reverted to a single gateway configuration to be sure that the issue
was not with the dual gateway config.
eth2 is my WAN interface, with address 217.221.234.74. My lan is
10.0.0.0/16, and I have a SNAT rule that says:
iptables -t nat -A POSTROUTING -o eth2 -j SNAT -s 10.0.0.0/16 --to-source
217.221.234.74
Running a simple "ethereal -i eth2 'not host 217.221.234.74'" I can see
that sometimes some packets go through WAN interface without being SNATed
by netfilter.
Tipically I can see a lot of correctly SNATed traffic, and once every
minute or so, some packets that seem to belong to an existent connection,
that go through with the original "from" address (in the 10.0.0.0/16
network)
this is an example taken from tethereal:
5062.581579 10.0.0.51 -> 207.68.178.134 TCP 1069 > www [FIN, ACK] Seq=0
Ack=0 Win=64526 Len=0
5062.581602 10.0.0.51 -> 207.68.178.134 TCP 1070 > www [FIN, ACK] Seq=0
Ack=0 Win=65535 Len=0
5063.687959 10.0.0.51 -> 207.68.178.134 TCP [TCP Retransmission] 1070 > www
[FIN, ACK] Seq=0 Ack=0 Win=65535 Len=0
5064.016036 10.0.0.51 -> 207.68.178.134 TCP [TCP Retransmission] 1069 > www
[FIN, ACK] Seq=0 Ack=0 Win=64526 Len=0
5066.094266 10.0.0.51 -> 207.68.178.134 TCP [TCP Retransmission] 1070 > www
[FIN, ACK] Seq=0 Ack=0 Win=65535 Len=0
5067.078602 10.0.0.51 -> 207.68.178.134 TCP [TCP Retransmission] 1069 > www
[FIN, ACK] Seq=0 Ack=0 Win=64526 Len=0
5070.906759 10.0.0.51 -> 207.68.178.134 TCP [TCP Retransmission] 1070 > www
[FIN, ACK] Seq=0 Ack=0 Win=65535 Len=0
5071.806521 10.0.0.51 -> 195.113.232.83 TCP 1065 > www [RST, ACK] Seq=0
Ack=0 Win=0 Len=0
5071.806642 10.0.0.51 -> 195.113.232.83 TCP 1067 > www [RST, ACK] Seq=0
Ack=0 Win=0 Len=0
5071.806657 10.0.0.51 -> 195.113.232.83 TCP 1066 > www [RST, ACK] Seq=0
Ack=0 Win=0 Len=0
5071.806765 10.0.0.51 -> 195.113.232.83 TCP 1068 > www [RST, ACK] Seq=0
Ack=0 Win=0 Len=0
5073.094312 10.0.0.51 -> 207.68.178.134 TCP [TCP Retransmission] 1069 > www
[FIN, ACK] Seq=0 Ack=0 Win=64526 Len=0
5077.923046 10.0.0.12 -> 207.68.178.239 TCP [TCP Retransmission] remoteping
> www [FIN, ACK] Seq=0 Ack=0 Win=64294 Le n=0
5080.531986 10.0.0.51 -> 207.68.178.134 TCP [TCP Retransmission] 1070 > www
[FIN, ACK] Seq=0 Ack=0 Win=65535 Len=0
5085.125717 10.0.0.51 -> 207.68.178.134 TCP [TCP Retransmission] 1069 > www
[FIN, ACK] Seq=0 Ack=0 Win=64526 Len=0
5099.782192 10.0.0.51 -> 207.68.178.134 TCP [TCP Retransmission] 1070 > www
[FIN, ACK] Seq=0 Ack=0 Win=65535 Len=0
5109.188539 10.0.0.51 -> 207.68.178.134 TCP [TCP Retransmission] 1069 > www
[FIN, ACK] Seq=0 Ack=0 Win=64526 Len=0
5116.244053 10.0.0.12 -> 207.68.178.239 TCP [TCP Retransmission] remoteping
> www [FIN, ACK] Seq=0 Ack=0 Win=64294 Le n=0
Is this a known bug of my kernel/netfilter version? Is there something I
can do to fix it?
Thanks.
--
Fabio "Kurgan" Muzzi
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