Plugging in LAN connection breaks ADSL Internet access

[Stuart]

We recently had broadband ADSL installed at our main and satellite offices -
both are tiny LAN set-ups which would periodically dial ISDN to enable
synchronisation of a line of business database.

Now with an ADSL router at either end the goal is to use VPN to achieve
synchronisation. At the main office with one server and seven clients, the
broadband internet works brilliantly with the server plugged into the router
*if* the router is not connected to the LAN hub. As soon as I connect the
router to the LAN via another port all Internet traffic stops - the LAN
still functions perfectly and all the clients are receiving perfectly valid
TCP/IP settings from the router. I cannot fathom why plugging in the LAN
should cause the Internet link to fail.

Clients are accepting routable IPs from a small CIDR range assigned by our
ISP, though if I switch to non-routable 192.168 addresses and try to use NAT
the situation still remains the same. I have spent a lot of time verifying
cabling and TCP/IP settings, but now I'm stumped as to how to further
troubleshoot the system.

I would be grateful for any suggestions about how to pin-point the problem -
eventually the parters plan to install Terminal Services at the main office
and use our clunky old local and remote machines as thin client terminals,
however we are totally stalled in the migration process.

Thanks in advance.

Stuart

 

[Marina Roos]

Are you using 2 nics in the server? Check the bindingorder and make sure the
internal nic is on top. Internal nic should have a blank gateway. External
nic should be on a different IP-range and the gateway should point to the
router-IP. External nic should only have TCP/IP bound to it.
DNS on both internal and external nic should point to your
server-IP. ISP-DNS-numbers should be set in tab Forwarders of DNS-server.
Also make sure you've done the regedits in 292822 as you're going to use
RRAS.
Check the options 003, 006, 015 in DHCP-server, Scope options. If you have
W9x, Me or NT4-clients, make sure WINS is installed on the server and add
options 044 and 046 (0x8).

Marina