Monday, January 30, 2006

PortForwarding on Linux .. the easy way - (not through SSH)

this info might not be tempting for home user with only one PC ... but it worth it for ppl who owns a few linux boxes in a large network ... there are many uses of portforwarding ... but i'll leave that to y'all to explore it ... in this thread, i'll explain 2 ways of doing portforwarding on linux ... i'll not cover portforwarding using iptables coz its quite hard to understand .. hehehe .. (i dun understand it oso) ...

OPTION 1: The easy and secure way : Using SSH portforwarding
this method is very easy ... however .. u'll need an SSH server running sumwhere in the network to create the tunnel ...

let assume the SSH server is called : mysshd.server
your pc is called : localhost
and the target PC is called : remote.system

if you want a port in localhost to forward its request to a port to remote.system use this command


$ ssh user@mysshd.server -L [localport]:remote.system:[remoteport]
** dont include the [ ]

this will open a port @ localhost:localport that redirects to remote.system:remoteport ...

if you want a port in mysshd.server to forward it requests to remote.system or another pc on the network ..


$ ssh user@mysshd.server -R [porttoopen]:remote.system:[targetport]
** dont include the [ ]

this will open a port @ mysshd.serverorttoopen that redirects to remote.system:targetport ...

NOTE: the requests are tunnelled through SSH protocol .. so .. its quite slower bcoz SSH encrypts all transactions .. but it is very secure this way ...

Minus point : this can only work to forward TCP connections ... it wont work for UDP

OPTION 2: Using Portfwd

theres a userspace program to do portforwarding on linux ... it is called portfwd .. u can get it from http://sourceforge.net/projects/portfwd/

extract it, compile, and install it ... by default the executable will be installed at /usr/local/sbin/portfwd ..

to forward a TCP connection ... create a plaintext file .. lets call it portfwd.cfg ... and insert these lines


tcp { [localport] { => remote.system:[remoteport] } }
** dont include the [ ]

then execute


# /usr/local/sbin/portfwd -c portfwd.cfg

this will open a TCP port @ localhost:localport to remote.system:remoteport

UDP forwarding is similar ... juz change tcp to udp in the config file ..

for more options .. read the manpages and the documentations

well ... think thats all .... enjoy!! ..

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