Duplicate Public IP Addresses?

[arvind doraiswamy <arvind.doraiswamy () gmail com>]

Hey Guys,
Maybe this is a bit of a basic question but I thought I'd ask here all
the same. Please let me know if this is too Non Firewall to be posted
:)

Over the years a lot of clients have used Public IP addresses on an
Internal network. So there's whole internal ranges with 80.x.x.x . Now
almost all of those systems do not have publicly reachable services at
all. Lets also assume that there is some website somewhere which has
the 80.x.x.x IP address assigned to it and people DO visit it and use
its "services". All ok so far.

What though if the internal network suddenly decided to make one of
his systems a web server , put a site onto it and pushed it on to the
Internet with the same 80.x.x.x address that was assigned to the
server when it was part of the Internal Network? Effectively it means
that now.. 2 servers ; the original web server (A) and the new web
server (B) both have an IP of 80.x.x.x (SAME).

Now I haven't done this practically and checked what will happen , but
I have a few questions in mind.

a) What happens to all the traffic going to A? Does it still go there
or do clients of A get redirected to B?
b) What about B wrt Question a) ?
c) What about DNS servers everywhere? What IP addresses will they
cache and how will they ensure that people are "routed" correctly?
d) Isn't this a very easy DOS condition? Anyone just changes IP ,
registers with their own DNS and sits back and waits?

Am I missing something? It just seems to easy to do..so I thought I'd
post here and get educated :)

Thnx
Arvind
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