Two-faced Security Problem? Dammit Janus?

[pcw@access.digex.net (Peter Wayner)]

Not exactly crypto, but the same idea:

I've been trying to hook up an HTTP server sitting on a Mac at the end of
my normal PPP connection. This was just supposed to be a test, but I kept
getting annoying connection problems whenever someone tried to GET a page
from me. The connection wouldn't go through about half of the time.

After poking around for a week, I discovered that my home machine,
newray.digex.net, is listed in the Digex's nameservers TWICE! Once with the
IP address that my home machine is waiting for (199.125.128.5) and once
with some other IP address in the digex space (164.109.211.61). If you do
an nslookup on the name, you get both addresses. I believe that the
technically correct thing for someone to do is to choose one of the
addresses at random to distribute the load between two machines pretending
to be one. This explains the connection failures that happened half of the
time.

This has led me to wonder, though, whether this is some sort of security
breech. For instance, could there be someone out there mascarading as me?
Normally I run Eudora, Netscape, Telnet and other outward bound
applications. It was almost a fluke that I noticed that there were two
entries.

Does some software need to find its IP address in a DNS table? For
instance, does Eudora need to look up  164.109.211.61 to find
"newray.digex.net"? If someone was using this software on the mascarading
node, they would need to set up an entry in the tables to make everything
work. They just assumed I would never get inbound traffic.

Any theories on this?

-Peter "More Paranoid Than Ever" Wayner