FQDN resolves externally but not internally

Hi,

I work in a building where there are 2 companies.
However we share the internet connection and the firewall.

Our ISP (BT) has given us 14 public static IP addresses.

Now, internally we're all on the same network but we use our own server for fileserving and webserving.
THe firewall software is WinRoute.

In the building there are 2 webservers, one that belongs to the other guys which has internal ip address of 192.168.2.252 the firewall has been setup to forward any requests from 217.xx.xx.17 (ive put in xx cos i wouldnt like to reveal the actual ip address, sorry to seem paranoid) to 192.168.2.252, i.e to their webserver.

the firewall and their webserver sit on the same pc. 192.168.2.252 and its default external address is 217.xx.xx.17

My webserver has an ip address of 192.168.2.254 internally.
THe firewall (which sits on 192.168.2.252 (winroute)) has been set to forward any requests from 217.xx.xx.21 ti 192.168.2.254

What a did was setup a sub domain

subdomain.mydomain.co.uk to point to 217.xx.xx.21. Which works fine on the outside. Everyone can access that ip address or sub-domain and see my webserver.

BUt internally, when i enter 217.xx.xx.21 or even subdomain.mydomain.co.uk, i get the other guys webserver instead. i.e 217.xx.xx.17 .

when i ping subdomain.mydomain.co.uk, it also returns 217.xx.xx.17 instead of 217.xx.xx.21 .

I added an entry into my host file to see if that would resolve the issue

i.e 192.168.2.254 subdomain.mydomain.co.uk

but that hasnt worked. can somebody please help me, or give me some direction

Thanks

edit your /etc/resolv.conf to use a (the) nameserver everybody from the outside does