On Thursday 11 October 2012 03:32 PM, Denys Fedoryshchenko wrote:
On 2012-10-11 12:57, Eric Dumazet wrote:
On Thu, 2012-10-11 at 12:41 +0300, Denys Fedoryshchenko wrote:
Hi all
I have NAT box, with very simple rule
iptables -t nat -I POSTROUTING -s 10.0.0.0/8 -j MASQUERADE
It can be SNAT also, and it works fine, as NAT.
When i generate icmp _reply_ packet, to some host
hping -I ppp0 -1 --icmptype 0 8.8.8.8
It will pass the box, and will exit it without NAT, e.g. with original
IP 10.x.x.x
on outgoing interface, which is not expected behavior IMHO.
Is it a bug or feature?
It depends, -s 10.0.0.0/8 wont match the rule if the source address
should be 198.23.44.55 I guess ?
I would try the more obvious
iptables -t nat -I POSTROUTING -o device -j MASQUERADE
Source is correct, it is 10.0.0.0/8 range. I tested also ICMP code 3,
it wont be NATed also.
But ICMP echo passing OK.
Also TCP RST generated same way, (i guess that don't have any match in
conntrack table), won't be NATed too.
hping -I ppp0 -R 8.8.8.8
13:01:07.074134 IP 10.0.0.142.2106 > 8.8.8.8.0: Flags [R], seq
510333079, win 512, length 0
13:01:08.074239 IP 10.0.0.142.2107 > 8.8.8.8.0: Flags [R], seq
1169580528, win 512, length 0
13:01:09.074253 IP 10.0.0.142.2108 > 8.8.8.8.0: Flags [R], seq
186548661, win 512, length 0
13:01:10.074376 IP 10.0.0.142.2109 > 8.8.8.8.0: Flags [R], seq
2135508128, win 512, length 0
13:01:11.074553 IP 10.0.0.142.2110 > 8.8.8.8.0: Flags [R], seq
1507433100, win 512, length 0
And ICMP here you can see correct behavior with icmp echo request:
12:58:22.917458 IP 10.0.0.142 > 8.8.8.8: ICMP echo reply, id 62548,
seq 0, length 8
12:58:23.917543 IP 10.0.0.142 > 8.8.8.8: ICMP echo reply, id 62548,
seq 256, length 8
12:58:24.917657 IP 10.0.0.142 > 8.8.8.8: ICMP echo reply, id 62548,
seq 512, length 8
12:58:31.047475 IP 10.0.0.142 > 8.8.8.8: ICMP net 5.6.7.8 unreachable,
length 36
12:58:32.047562 IP 10.0.0.142 > 8.8.8.8: ICMP net 5.6.7.8 unreachable,
length 36
12:58:33.047734 IP 10.0.0.142 > 8.8.8.8: ICMP net 5.6.7.8 unreachable,
length 36
12:58:54.014601 IP X.146.153.X > 8.8.8.8: ICMP echo request, id 10462,
seq 0, length 8
12:58:54.081897 IP 8.8.8.8 > X.146.153.X: ICMP echo reply, id 10462,
seq 0, length 8
I think, the following may be the reason for the behaviour you observed.
(I may be wrong, I am not an expert in iptables.)
"nat" table only consulted for "NEW" connections. ref:
<http://inai.de/images/nf-packet-flow.svg>
The ICMP echo _reply_ may not be considered as part of a "NEW"
connection, as it must be a _reply_ to some already received _request_.
So _request_ is new and _reply_ is not.
Regards,
Vignesh
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