How to redirect/forward port traffic from a
certain port to another on Linux
In the University where I study right now
Arnhem Business School
(ABS) the outbound traffic to
port numbers 25, 110 and
995 are filtered.
This is quite unhandy counting the fact that I'm completely
dependable to read both my school and job mails via the nice SMTP
and POP3 protocols with Thunderbird (Icedove) as called in
Debian.
Therefore I looked for a good way to create a port redirect from
the
filtered 25, 110 and 995 to allowed outbound
ports.
A quick
nmap port scan revealed me
that the three outbound
ports 2010 and 2050 and 2060 are
allowed to pass network traffic.
Therefore after some research on forums onine and some consulting
in
irc.freenode.net I've found a way to add a redirect rule
with iptables.
Below are the three rules I used to redirect my
ports 25,110 and
995 to
port numbers 2010 2050 and 2060 on localhost
where a qmail mail server is serving my mail
debian:~# /sbin/iptables -t nat -I PREROUTING -p tcp --dport
2050 -j REDIRECT --to-ports 25
debian:~#
debian:~# /sbin/iptables -t nat -I PREROUTING -p tcp --dport 2010
-j REDIRECT --to-ports 110
debian:~#
debian:~# /sbin/iptables -t nat -I PREROUTING -p tcp --dport 2060
-j REDIRECT --to-ports 995
debian:~#
That's all now I just had to change the configuration in my
Thunderbird client and set the
ports 2050, 2010 and
2060 in place of the normal
25, 110, 995