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Re: DNAT TCP 12345 -> 22

On 2008-03-20 Frédéric Massot wrote:
> I have servers with public IP addresses in a DMZ behind a firewall.
> The firewall has two network interface, one connected to the DMZ, the
> other to the ISP router.
> From local network, I can access the server via SSH on port 22/TCP.
> I would like to access the server from the outside on another port
> like 12345/TCP. I try to translate the SSH port on the firewall with a
> DNAT rule.
> I have these rules :
> tcp --sport $UNPRIVPORTS -d $SERVER --dport 22 -m state --state NEW -j
> iptables -t nat -A PREROUTING -i $EXTERNAL_INTERFACE -p tcp -d $SERVER
> --dport 12345 -j DNAT --to-destination $SERVER:22
> With these rules I can access the server on ports 22/TCP and
> 12345/TCP.
> How I can ensure that access will possible only on port 12345/TCP and
> not on port 22/TCP ?

Have your sshd listen on both ports, and allow only 12345/tcp inbound on
your external firewall.

Ansgar Wiechers
"The Mac OS X kernel should never panic because, when it does, it
seriously inconveniences the user."

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