[ILUG] Mystery POP mail problem (connections refused to 192.168.*.* numbers)

[Kenn Humborg]

Joe Desbonnet wrote:
> 
> Does anyone know whats happening here? This is on a Linux (RH5.0) machine
> which has happily collected email (via dialup) and acted as a local POP
> server for the last 2 years. All of a sudden (yesterday) the machine starts
> refusing access to the local computers on the LAN (using 192.168.6.* IP
> numbers). The strange thing is that *occasionally* it does allow access.
> 
> Its using a tinet nameserver. And what is this
> read-rfc1918-for-details.iana.net host name (I know RFC 1918 refers
> to the 192.168.* allocations) but the where that host name comes
> from I have no idea.

If you're going to use 192.168 networks, you should provide your
own reverse-DNS.  In your case, you should be able to get
away with an /etc/hosts file as long as /etc/host.conf has
order=hosts,bind.

The pop server is doing a 'double reverse lookup' to check the
connection.  In fact, it's tcpwrappers that are doing it.  So 
you might get by for a while by removing entries for ipop3d
from /etc/hosts.{allow,deny}.  That might stop the name lookups.

In the long term, you'll need an internal DNS server.  See
http://www.linux.ie/intersocs98/talks/UsingLinuxAsAGateway/
for more details :-)

Kenn