Domain Name Service (DNS), though typically invisible to the user, is the most fundamental tool associated with use of the Internet. The Internet uses the IP protocol and all IP traffic must have a source host address and a destination host address in the form of 207.193.0.0. Unfortunately, these addresses are extremely cumbersome and nearly impossible to remember.

The function of DNS is to map the required IP addresses into more user-friendly, easy-to-remember host names. For example, the IP address of the SBCIS mail server could be 207.193.0.1, but its associated host name is swbell.net. DNS allows users to document the correlation between their IP addresses and host names. Each site is responsible for documenting the correlation between their own IP addresses and host names. This information is then propagated to other DNS servers all over the world. Everyone on the Internet relies on this mapping to easily access hosts and resources.

Also since hosts at a specific site are associated with a specific IP network address, all hosts at that site can be grouped together into a single domain. In this way, many Internet sites can reuse a host name such as "compass", as long as they each belong to different domains. To clarify, compass.pacbell.net does not correspond to the same IP address as compass.pacbell.com, since the domain "pacbell.net" is associated with the 207.11.1.0 network and the domain "pacbell.com" is associated with the 157.164.4.0 network. Of course, two computers cannot have the same host name if they are part of the same domain.

One or more hosts running specialized software provide the DNS for a particular site; these hosts are commonly referred to as name servers or domain name servers. Customers are responsible for providing one primary name server at their location or they can choose to use SBCIS' optional Primary DNS service.

As part of our basic service, SBCIS offers Dedicated Access customers the option of using one of our name servers as a primary or secondary name server, for one fully qualified domain per customer. There is no additional charge for secondary DNS and a nominal charge for primary DNS services. The advantage of such a configuration is that if the primary name server fails, the SBCIS name server can provide the required mapping between host names and IP addresses.

Without a secondary name server, the site would be virtually isolated from the rest of the Internet. Remote users would find hosts at that site to be unresponsive to their host names. Likewise, local users trying to reach any host would be forced to manually enter the destination IP address in place of its host name. Please note that not providing DNS is NOT a security feature; it will not prevent your site from receiving data since the IP addresses for your site can easily be found or guessed.