Each name requested from a DNS server consists of different parts: One part consists of the actual name of the host or service to be reached, another part identifies the domain. Within a local network, specifying the domain is optional. Examples of these names would be "www.domain.com" or "ftp.domain.com".
Without a DNS server in the local network, every name that is not known locally would be searched for on the default route. By using a DNS server, any name that has a known IP address can be found directly at the correct peer. In principle, the DNS server can be a separate computer in the network. However, the DNS server is best located directly in the device for the following reasons:
- When operated as a DHCP server, the device can independently distribute the IP addresses for the computers in the local network. The DHCP server is therefore already familiar with all of the computers on its own network by their computer name and IP address. An external DNS server might have difficulties keeping the relationships between IP address and name up to date in case of dynamic address assignment by the DHCP server.
- When routing Windows networks via NetBIOS, the device also knows the computer names and IP addresses in the other networks connected via NetBIOS. Furthermore, computers with a fixed IP address can also enter themselves into the NetBIOS table to make their names and addresses known.
- The DNS server in the device can also be used as a convenient filter mechanism. Requests for undesirable domains can be blocked for the entire LAN, for certain subnets only, or even for individual computers, simply by specifying the domain name.
