Redirecting internal tcp connections

Jose Maria Lopez Hernandez jkerouac at bgsec.com
Fri Apr 15 19:57:56 CEST 2005


El vie, 15-04-2005 a las 14:12 -0300, marcus escribió:
> Hi, I have a lpd server on a remote host that ISP blocks port 515. I try 
> to use something like "lpr -Plp at remotehost.com:900" but lprng doenst 
> seems to recognize the port argument. So, I think to use iptables to 
> redirect TCP requests on port 515 to port 900 but I dont know how. I've 
> tried the following:
> 
> #iptables -A OUTPUT -p tcp --dport 515 -j REDIRECT --to-port 900
> 
> This gives me a "iptables: Invalid argument"
> 
> Any ideas?

You have to do this in the nat table and the prerouting or
output chain, and you should use DNAT instead of REDIRECT,
because REDIRECT is for packets with destination your own
machine. So we have:

iptables -t nat -A PREROUTING -p tcp --dport 515 -j DNAT --to-
destination remotehost.com:900

Regards.

-- 

Jose Maria Lopez Hernandez
Director Tecnico de bgSEC
jkerouac at bgsec.com
bgSEC Seguridad y Consultoria de Sistemas Informaticos
http://www.bgsec.com
ESPAÑA

The only people for me are the mad ones -- the ones who are mad to live,
mad to talk, mad to be saved, desirous of everything at the same time,
the ones who never yawn or say a commonplace thing, but burn, burn, burn
like fabulous yellow Roman candles.
                -- Jack Kerouac, "On the Road"





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