we have a DNS server with the domain ddd.no
we have two domains that we use to point our users to our web servers www.ddd.no
now we bought and external web hosting plan (to build some sites outside our network) whish is test.ddd.no & portal.ddd.no
how we can make things work that users in the LAN have normal access to the old sites with no problem and if some one use portal.ddd.no then it will point him to the external site.
with no need to configure portal.ddd.no & test.ddd.no in our DNS server (the internal server on our LAN)
what I mean if the sub-domain test , portal or what ever sub-domain if it in not configured on our DNS server then it will look for it in the internet.