[PLUG] DNS trouble and something called protocol 17.

[Bill]

As for your question about using a mail server on a private ip address, 
you just need to set up port forwarding for smtp and pop3/imap.  If your 
firewall is based in a 2.2.x kernel you would use commands like

ipmasqadm portfw -f
ipmasqadm portfw -a -P tcp -L (yer external ip here) 25 -R (yer internal 
private ip here) 25

This will forward ALL the port 25 stuff coming into the external interface 
to the machine you designate by the second, private, ip.  Then you gotta 
do the same for port 110 for pop3 and whatever port imap uses.  

The problem is most 2.2 kernels don't have portfw enabled, so you'll 
probably have to roll yer own.  2.4 kernels are supposed to be more likely 
to have portforwarding compiled in by default, but I don't have experience 
using them as a firewall yet.  

Best thing is to go to the ip masq how to at www.linuxdoc.org, which is 
where I always go when I have to figure out how to do anything with ip 
masq.  The BSDs also do port forwarding, and some would argue that they 
are more secure.  Not me, cause I haven't played with them yet.

www.linuxdoc.org/HOWTO/IP-Masquerade-HOWTO