Port-Forwarding With rinetd On Debian Etch

1 Preliminary Note
In this example I'm trying to redirect HTTP traffic (port 80) from the IP address 192.168.0.101 to the IP address 192.168.0.100.
Please note that rinetd is not able to redirect FTP because FTP requires more than one socket.

2 Installing And Configuring rinetd
To install rinetd, we simply run
apt-get install rinetd
rinetd's configuration file is /etc/rinetd.conf. To forward HTTP traffic from 192.168.0.101 to 192.168.0.100, we add the line 192.168.0.101 80 192.168.0.100 80:
vi /etc/rinetd.conf
#
# this is the configuration file for rinetd, the internet redirection server
#
# you may specify global allow and deny rules here
# only ip addresses are matched, hostnames cannot be specified here
# the wildcards you may use are * and ?
#
# allow 192.168.2.*
# deny 192.168.2.1?

#
# forwarding rules come here
#
# you may specify allow and deny rules after a specific forwarding rule
# to apply to only that forwarding rule
#
# bindadress    bindport  connectaddress  connectport
192.168.0.101 80 192.168.0.100 80
# logging information
logfile /var/log/rinetd.log
# uncomment the following line if you want web-server style logfile format
# logcommon
Then we restart rinetd:
/etc/init.d/rinetd restart
Now run
netstat -tap
and you should see that rinetd is listening on port 80 (www):
server2:~# netstat -tap
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 *:sunrpc                *:*                     LISTEN     1956/portmap
tcp        0      0 server2.example.com:www *:*                     LISTEN     2485/rinetd
tcp        0      0 *:3025                  *:*                     LISTEN     2347/rpc.statd
tcp        0      0 *:auth                  *:*                     LISTEN     2306/inetd
tcp        0      0 localhost.localdom:smtp *:*                     LISTEN     2294/exim4
tcp6       0      0 *:ssh                   *:*                     LISTEN     2326/sshd
tcp6       0      0 server2.example.com:ssh ::ffff:192.168.0.3:4776 ESTABLISHED2409/0
server2:~#


Now when you direct your browser to a web page on the IP address 192.168.0.101, it should receive that page from the server with the IP address 192.168.0.100.
Instead of specifiying the port numbers in /etc/rinetd.conf, you can also use the service names. The service names are stored in /etc/services, so when you open that file, you will see that the service for port 80 is named www on Debian.
grep 80 /etc/services
server2:~# grep 80 /etc/services
www             80/tcp          http            # WorldWideWeb HTTP
www             80/udp                          # HyperText Transfer Protocol
socks           1080/tcp                        # socks proxy server
socks           1080/udp
amanda          10080/tcp                       # amanda backup services
amanda          10080/udp
omirr           808/tcp         omirrd          # online mirror
omirr           808/udp         omirrd
canna           5680/tcp                        # cannaserver
zope-ftp        8021/tcp                        # zope management by ftp
webcache        8080/tcp                        # WWW caching service
tproxy          8081/tcp                        # Transparent Proxy
omniorb         8088/tcp                        # OmniORB
omniorb         8088/udp
server2:~#
So you could use the following configuration in /etc/rinetd.conf, it has the same effect as the first one:
vi /etc/rinetd.conf
#
# this is the configuration file for rinetd, the internet redirection server
#
# you may specify global allow and deny rules here
# only ip addresses are matched, hostnames cannot be specified here
# the wildcards you may use are * and ?
#
# allow 192.168.2.*
# deny 192.168.2.1?

#
# forwarding rules come here
#
# you may specify allow and deny rules after a specific forwarding rule
# to apply to only that forwarding rule
#
# bindadress    bindport  connectaddress  connectport
192.168.0.101 www 192.168.0.100 www
# logging information
logfile /var/log/rinetd.log
# uncomment the following line if you want web-server style logfile format
# logcommon
And to make rinetd listen on all IP addresses that are configured on the system where it is installed, we can use 0.0.0.0 as the bindaddress:
vi /etc/rinetd.conf
#
# this is the configuration file for rinetd, the internet redirection server
#
# you may specify global allow and deny rules here
# only ip addresses are matched, hostnames cannot be specified here
# the wildcards you may use are * and ?
#
# allow 192.168.2.*
# deny 192.168.2.1?

#
# forwarding rules come here
#
# you may specify allow and deny rules after a specific forwarding rule
# to apply to only that forwarding rule
#
# bindadress    bindport  connectaddress  connectport
0.0.0.0 80 192.168.0.100 80
# logging information
logfile /var/log/rinetd.log
# uncomment the following line if you want web-server style logfile format
# logcommon
After you've restarted rinetd...
/etc/init.d/rinetd restart
... rinetd should now listen on all interfaces (*:www):
netstat -tap
server2:~# netstat -tap
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 *:sunrpc                *:*                     LISTEN     1956/portmap
tcp        0      0 *:www                   *:*                     LISTEN     2503/rinetd
tcp        0      0 *:3025                  *:*                     LISTEN     2347/rpc.statd
tcp        0      0 *:auth                  *:*                     LISTEN     2306/inetd
tcp        0      0 localhost.localdom:smtp *:*                     LISTEN     2294/exim4
tcp        0      0 server2.example.com:www 192.168.0.3:4798        TIME_WAIT  -
tcp6       0      0 *:ssh                   *:*                     LISTEN     2326/sshd
tcp6       0    148 server2.example.com:ssh ::ffff:192.168.0.3:4776 ESTABLISHED2409/0
server2:~#


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