problem in asp.net session and authentication with network

[Ken Tech]

I got some problem on session and authentication on asp.net web site as
describe below

First Scenario
Develop on developper machine (windows 2000 Prof)
- Website reside on Virtual directory of Deffault website
(localhost/[asp.net_site]/start.aspx)

When move to
Staging Server (windows 2000 server)
- Create virtual Website (in addition of Default website which has been
stopped) with different IP (same port 80). (DNS or Computer/start.aspx)

Request.IsAuthenticated does not work when using DNS name(Map to the new IP
create on stagining server) or Computer Name but work fine if browsing with
IP (IP/start.aspx)

Second Scenario
First Scenario
Develop on developper machine (windows 2000 Prof)
- Website on Virtual directory of Deffault website

When move to
Staging Server (windows 2000 server)
- Create virtual directory inside default web site.
- Server also acting as router (contains 2 NIC) for linking between 2
network

asp.net Session loss when Client browser browse from outside network (Main),
work fine when browsing from Client inside network(NAT)

Does anyone got the same problems?

Ken