We have always run one subnet 10.0.0.0 with a DNS server of 10.0.0.20 with less than 20 clients, shortly we have another company moving into the office sharing the same structured cabling, however I would like to keep them on a different subnet.
We have allocated them with one of the WAN IPs made available to us by our ISP by introducing a switch that each subnet's firewall plugs in to, those Firewalls are 10.0.0.1 and 192.168.16.1. All works well, but some of the PC's on 10.0.0.1 (typically those that are DHCP) try to use 192.168.100.1 for DNS and fail I cannot work out why they are trying to use it though.
DHCP is disabled for 192.168.16.x, it is not a domain and the IP config of all the clients on 10.0.0.0 seems fine, all pointing at 10.0.0.20 for DNS.
If anyone could tell me where I am being stupid that would be great.