Trouble shooting for port forwarding , Want to make sure port is forwarded

Trouble shooting for port forwarding , Want to make sure port is forwarded

[John Joseph]

Hi 
    For the purpose of trouble shooting  , one  setup
which I had done  for redirecting port 110 to port
8110 ( same machine)  . For this purpose   I gave the
command as 

iptables -t nat -A PREROUTING  -p tcp --dport 110 -j
REDIRECT --to-port  8110

   Now after this . When I do a tcpdump for port 8110
, I do not get any results , when I  access port 110 
                
        Since the tcpdump results for  port 8110  is
not  seen , what can we conclude from , Is port
forwarding happening here ?
                      Thanks 
                            Joseph John 


		
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Re: Trouble shooting for port forwarding , Want to make sure port is forwarded

[Guillaume]

John Joseph wrote:
> Hi 
>     For the purpose of trouble shooting  , one  setup
> which I had done  for redirecting port 110 to port
> 8110 ( same machine)  . For this purpose   I gave the
> command as 
> 
> iptables -t nat -A PREROUTING  -p tcp --dport 110 -j
> REDIRECT --to-port  8110
> 
>    Now after this . When I do a tcpdump for port 8110
> , I do not get any results , when I  access port 110 
>                 
>         Since the tcpdump results for  port 8110  is
> not  seen , what can we conclude from , Is port
> forwarding happening here ?
>                       Thanks 
>                             Joseph John 
> 
> 
> 		
> ___________________________________________________________ 
> Try the all-new Yahoo! Mail. "The New Version is radically easier to use" – The Wall Street Journal 
> http://uk.docs.yahoo.com/nowyoucan.html
> 

Hi,

After enabling a dnat traffic, you need to allow it in the "filter" 
table with a rule that look like this:
iptables -t filter -A INPUT -p tcp --dport 8110 -j ACCEPT

Regards
Guillaume


-- 
Guillaume
E-mail: silencer_<at>_free-4ever_<dot>_net
Blog: http://guillaume.free-4ever.net
----
Site: http://www.free-4ever.net

Re: Trouble shooting for port forwarding , Want to make sure port is forwarded

[Pascal Hambourg]

Hello,

John Joseph a écrit :
> Hi 
>     For the purpose of trouble shooting  , one  setup
> which I had done  for redirecting port 110 to port
> 8110 ( same machine)  . For this purpose   I gave the
> command as 
> 
> iptables -t nat -A PREROUTING  -p tcp --dport 110 -j
> REDIRECT --to-port  8110
> 
>    Now after this . When I do a tcpdump for port 8110
> , I do not get any results , when I  access port 110 

This is normal. Tcpdump sees the incoming original packets when they 
arrive at the interface, before they are DNATed or REDIRECTed by 
iptables in the PREROUTING chain.