How to log NAT translations

DISCUSSION Italo Valcy 4 participants 6 messages Sep 14, 2010 – Sep 21, 2010

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Italo Valcy

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2010-09-14 17:24 UTC #0 lore raw

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Hi guys!

I'm a newbie in this mainling list, so I'm sorry if this question was already asked.

I'd like to have more specific logging output of NAT translation in iptables. Is there an way to logging of ORIGINAL_IP/ORIGINAL_PORT + TRANSLATED_IP/TRANSLATED_PORT?

I know that I can put a logging rule before my NAT rule, but this way I haven't the TRANS_IP/TRANS_PORT... for instance:

iptables -t nat -I POSTROUTING -s 10.0.0.0/24 -j SNAT --to 172.16.0.1 iptables -t nat -I POSTROUTING -s 10.0.0.0/24 -j LOG

In the above example I don't know how to get the TRANS_PORT...

I also know that we can access this information through /proc/net/ip_conntrack (or using netstat-nat), but to get all translation of a whole day its a big overhead to parse that file all the time...

Thanks for any help!

- --
Saudações,

Italo Valcy :: http://wiki.dcc.ufba.br/~ItaloValcy
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Jan Engelhardt

2010-09-14 17:54 UTC #1 lore raw

Quoted 11 lines · Italo Valcy

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Hi guys!
I'm a newbie in this mainling list, so I'm sorry if this question was already asked.
I'd like to have more specific logging output of NAT translation in iptables. Is there an way to logging of ORIGINAL_IP/ORIGINAL_PORT + TRANSLATED_IP/TRANSLATED_PORT?

conntrack -E

Italo Valcy

author

2010-09-21 02:25 UTC #2 lore raw

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Hi Jan,

Em 14-09-2010 14:54, Jan Engelhardt escreveu:

Quoted 7 lines · Italo Valcy

Quoted 6 lines
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Hi guys!

Quoted 8 lines

Quoted 6 lines
I'm a newbie in this mainling list, so I'm sorry if this question was already asked.
I'd like to have more specific logging output of NAT translation in iptables. Is there an way to logging of ORIGINAL_IP/ORIGINAL_PORT + TRANSLATED_IP/TRANSLATED_PORT?
conntrack -E

Thank you for the reply.

Actually, I wanna something more simple and specific than the command above. Using 'conntrack -E', I still have to parse the package events NEW, UPDATE and DESTROY if I wanna know the of a NAT, for example. Furthermore, with 'conntrack -E', in my opinion, we have an important overhead of the output (it's so many messages to write to stdout - or even redirect to a file)...

My ideia is to write a NAT (or conntrack) helper (as a kernel module) that monitors the DESTROY event of a DNAT and try to find out when was the NEW event of the same connection (maybe we have this information in some struct..); then we write a log message (like LOG target does) which contains ip_src-orig/port_src-orig, ip_src-translated/port_src-translated, ip_dst/port_dst, duration of the NAT (a little bit similar to Cisco/Asa NAT logging..). What do you think? Where can I find some documentation to read?

Thank you so much for any help!

- --
Saudações,

Italo Valcy :: http://wiki.dcc.ufba.br/~ItaloValcy
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Jan Engelhardt

2010-09-21 09:26 UTC #3 lore raw

Quoted 3 lines · Italo Valcy

Actually, I wanna something more simple and specific than the command above. Using 'conntrack -E', I still have to parse the package events NEW, UPDATE and DESTROY if I wanna know the of a NAT

So use conntrack -Ee NEW to limit the output :)
If that is still too much overhead, I'm sure you can directly use libnetfilter_conntrack's library interface to get at these events.

Pablo Neira Ayuso

2010-09-21 09:45 UTC #4 lore raw

Quoted 9 lines · Jan Engelhardt

Quoted 3 lines · Italo Valcy
Actually, I wanna something more simple and specific than the command above. Using 'conntrack -E', I still have to parse the package events NEW, UPDATE and DESTROY if I wanna know the of a NAT
So use conntrack -Ee NEW to limit the output :)
If that is still too much overhead, I'm sure you can directly use libnetfilter_conntrack's library interface to get at these events.

You can refine this a bit more with:

`conntrack -Ee NEW --any-nat'

It was introduced in conntrack-tools-0.9.15.

Jozsef Kadlecsik

2010-09-21 10:22 UTC #5 lore raw

Quoted 7 lines · Pablo Neira Ayuso

Quoted 6 lines · Jan Engelhardt
Quoted 3 lines · Italo Valcy
Actually, I wanna something more simple and specific than the command above. Using 'conntrack -E', I still have to parse the package events NEW, UPDATE and DESTROY if I wanna know the of a NAT

Quoted 7 lines

Quoted 3 lines
So use conntrack -Ee NEW to limit the output :)
If that is still too much overhead, I'm sure you can directly use libnetfilter_conntrack's library interface to get at these events.
You can refine this a bit more with:
`conntrack -Ee NEW --any-nat'

Yes, but it's strange to use 'conntrack' for logging. Isn't it simpler to use ulogd2 and the ulogd_inpflow plugin?

Best regards,
Jozsef
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