Petr Pisar wrote:
lukas@xxxxxxxxxxx wrote:
NAT configuration is simple but some packets are not NATed - on my
public interface packets with source address of my internal (NATed)
network appears and i have no clue what is wrong.
16:30:39.015880 IP (tos 0x0, ttl 127, id 28594, offset 0, flags [DF],
proto: TCP (6), length: 40) 10.10.10.104.3689 > 83.29.48.50.6881: F,
cksum 0x1623 (correct), 3885889894:3885889894(0) ack 3151418643 win 65535
Exactly. I can see only FIN packets which are not translated. After
looking into conntrack table, I think MASQ ignores FIN packets that are
missing in conntrack table (Is it INVALID or NEW state?).
So, I'm able to reproduce this bug. Simply send untracked FIN pakcet
from intranet station to the Internet:
$ hping2 -c 1 -F 1.2.3.4
HPING 1.2.3.4 (eth1 1.2.3.4): F set, 40 headers + 0 data bytes
--- 1.2.3.4 hping statistic ---
1 packets tramitted, 0 packets received, 100% packet loss
round-trip min/avg/max = 0.0/0.0/0.0 ms
And dump traffic on your gateway:
$ tcpdump -i ppp0 -n net 192.168.0.0/24
tcpdump: listening on ppp0
20:30:36.304397 192.168.0.2.1039 > 1.2.3.4.0: F 2063212909:2063212909(0)
win 512
Very strange behaviour have counters too. These strange packets are not
loggable after MASQ rule. It seems like a bug.
Here is my POSTROUTING chain (ppp0 is public interface):
Chain POSTROUTING (policy ACCEPT 783 packets, 126K bytes)
pkts bytes target prot opt in out source
destination
897 54437 LOG all -- * * 0.0.0.0/0
0.0.0.0/0 LOG flags 2 level 4 prefix `PRE'
4531 365K MASQUERADE all -- * ppp0 0.0.0.0/0
0.0.0.0/0
38 2258 LOG all -- * * 0.0.0.0/0
0.0.0.0/0 LOG flags 2 level 4 prefix `POST'
and after doing this excercise I can't see any change on counters in
POSTROUTING chain. Naturaly I can't see anything in the kernel log (as
you can see, I log everything before MASQ and after that).
I seems, these magic packets are completly bypassing POSTROUTING chain.
I found out too that TCP traffic goes inside this chain only with first
SYN packet. After that there the packets are I don't see them anymore.
Is it normal?
-- Petr
