10 Port Forwarding

By:

Stephen Carville

Rev:

08/23/02

Port Forwarding is also possible using OpenSSH (Sec 17.2).

10.1 Using xinetd redirect function

The simpliest and, in my opinion, the preferred way to handle redirecting unencrypted connections is to use the redirect capability built into xinetd.

If necessary, add services names to /etc/services. For example:
geofwd  50005/tcp           # GeoTrac forwarded port

1. Add service file to /etc/xinetd.d. Example file:
   # default: on 
   # description: forward connections to indian:1005 
   service geofwd 
   { 
      flags = REUSE 
      socket_type = stream 
      wait = no 
      user = root 
      redirect = 192.168.124.4 1005 
      log_on_failure += USERID 
   }
2. Restart xinetd
   # /etc/rc.d/init.d/xinetd restart

10.2 Using Netcat

The netcat utility is sometimes described as the 'Swiss Army Knife'' of the network. Here we are using it for very basic port forwarding from an externally accessible server to an internal server. If it is not necessary to run the forwarding service continiously, on Redhat it is prefereable to use xinetd forwarding.

1. Install netcat from CDROM or from ftp
   # rpm -Uvh ftp://volga/pub/RPMS/nc-*.rpm
2. Add services names to /etc/services. For example:
   geofwd  50005/tcp           # GeoTrac forwarded port(netcat)
3. Add service file to /etc/xinetd.d. Example file:
4. # default: on 
   # description: forward connections to panama:1005 
   service geofwd 
   { 
      flags = REUSE 
      socket_type = stream 
      wait = no 
      user = root 
      server = /usr/bin/nc 
      server_args = 192.168.124.38 1005 
      log_on_failure += USERID 
   }
5. Restart xinetd
   # /etc/rc.d/init.d/xinetd restart