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Objective: When an external (ie, wlan) connection is attempted to
port 26 on the radio, forward that traffic ("destination NAT") to a
computer on my internal LAN.<br>
<br>
Firewall rules in the radio (rules #3 & #7 in the filter chain,
and rule #1 in the NAT chain, have been inserted by me):<br>
<br>
<font color="#3333ff"><i><tt><small>/ip firewall filter print<br>
Flags: X - disabled, I - invalid, D - dynamic<br>
0 ;;; default configuration<br>
chain=input action=accept protocol=icmp
src-address=44.0.0.0/8<br>
<br>
1 ;;; default configuration<br>
chain=input action=accept connection-state=established<br>
<br>
2 ;;; default configuration<br>
chain=input action=accept connection-state=related<br>
<br>
3 chain=input action=accept protocol=tcp
in-interface=wlan1-gateway dst-port=26<br>
<br>
4 ;;; default configuration<br>
chain=input action=drop in-interface=wlan1-gateway<br>
<br>
5 ;;; default configuration<br>
chain=forward action=accept
connection-state=established<br>
<br>
6 ;;; default configuration<br>
chain=forward action=accept connection-state=related<br>
<br>
7 chain=forward action=accept protocol=tcp
in-interface=wlan1-gateway dst-port=26<br>
<br>
8 ;;; default configuration<br>
chain=forward action=drop connection-state=invalid<br>
<br>
/ip firewall nat print<br>
Flags: X - disabled, I - invalid, D - dynamic<br>
0 ;;; default configuration<br>
chain=srcnat action=masquerade to-addresses=0.0.0.0
out-interface=wlan1-gateway<br>
<br>
1 chain=dstnat action=dst-nat to-addresses=192.168.0.250
protocol=tcp in-interface=wlan1-gateway dst-port=26</small></tt></i></font><br>
<br>
I use the same technique on my Linux boxes, and it works fine
(albeit iptables is slightly different). However, when accessing my
radio from an external IP address, no connection is made (times
out). If I change the dstnat rule action to "accept", the
connection is refused. The logs for port 26 on the target device
(192.168.0.250) show no connection attempt. In the (default) srcnat
chain, "action=masquerade" implies NATting on the return trip (into
the LAN). The same thing needs to happen in a dstnat chain, but I
don't see a way to do that; I'm "assuming" that the OS
automatically does that. When doing DNAT on Linux, I have to do
that manually, with the same rule in the "PREROUTING" and "OUTPUT"
NAT chains, but those chains don't exist in my radio.<br>
<br>
Ideas welcome (note that "action=masquerade" is not valid in a
dstnat chain).<br>
<br>
-- Dean<br>
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