How to log NAT translations

How to log NAT translations

[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?

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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Re: How to log NAT translations

[Jan Engelhardt]

On Tuesday 2010-09-14 19:24, Italo Valcy wrote:

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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

Re: How to log NAT translations

[Italo Valcy]

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Hi Jan,

Em 14-09-2010 14:54, Jan Engelhardt escreveu:
> On Tuesday 2010-09-14 19:24, Italo Valcy wrote:
> 
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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

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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Re: How to log NAT translations

[Jan Engelhardt]

On Tuesday 2010-09-21 04:25, Italo Valcy wrote:

>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.

Re: How to log NAT translations

[Pablo Neira Ayuso]

On 21/09/10 11:26, Jan Engelhardt wrote:
> On Tuesday 2010-09-21 04:25, Italo Valcy wrote:
> 
>> 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.

Re: How to log NAT translations

[Jozsef Kadlecsik]

On Tue, 21 Sep 2010, Pablo Neira Ayuso wrote:

> On 21/09/10 11:26, Jan Engelhardt wrote:
> > On Tuesday 2010-09-21 04:25, Italo Valcy wrote:
> > 
> >> 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'

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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