JANET Off-site Resolver Service

Resolvers are programs that handle the process of DNS resolution, i.e. looking up the name of a computer within your domain. A client program, such as a web browser, will contact a resolver with a request for a look-up, for example to find the numeric IP address equivalent to a given Internet name. The resolver formulates a DNS query that will answer the client's request and send that query to the appropriate nameserver to find the required information. When the resolver receives the answer to the query, it returns the information to the original client computer. Every computer on a local network must be able to contact a resolver before it can look up information in the DNS; the IP address of the resolver (and possibly also a backup resolver) must be entered into the computer as part of its initial configuration. Resolvers must be able to contact nameservers elsewhere on the Internet so they can work through the tree of Internet names to find the nameserver able to answer each individual query.

Resolver activity is therefore quite different from authoritative nameserver activity, though the two functions can often be provided by a single computer. If a primary or secondary nameserver is within the local network then it may be possible to have it act as a resolver for local clients. It is not recommended to allow a local nameserver to act as a general resolver for external clients as this may conflict with its most important function.

Note: The above is a heavily simplified description of part of the DNS, intended only to explain the purpose and limitations of the JANET Off-site Resolver Service. For more complete information, please consult these references.

What does the Service offer?

JANET(UK) recommends that each JANET organisation should have at least one resolver locally in its own campus network unless some good reason makes that impracticable. If a client computer cannot contact a resolver then it will in practice be cut off from the Internet and possibly from other computers in the same network.

Nevertheless JANET(UK) accepts that there is a requirement for a central last-resort service. Organisations with very small networks may find it appropriate to use an off-site resolver, and JANET(UK) has set up this service for their benefit. Dedicated resolvers located in the core of JANET will answer queries for domain name resolution that come from client computers on a customer organisation's network. Access to these servers is enabled only for the JANET IP addresses of those organisations which have registered for the service. Note that this service is intended to support e-mail and web use by a customer organisation, but not to resolve local queries, such as name resolution for a local printer, which should be done through local name directories if a local DNS service is not used.