Local DNS resolver
A local DNS resolver is standard piece of software installed on the server performing DNS lookups that can lookup the Fully Qualified Domain Name (FQDN) for any IP address. This software is available from the OS vendors of all OSes supported with ASL and is normally installed on most systems, and by all known control panels. If you are not sure if your system has a local resolver, please ask your OS or control panel vendor to confirm.
Examples of this include:
- Local caching DNS server
- Local installation of the Berkeley Internet Name Domain (BIND) DNS (Domain Name System) server
In both of these examples, the DNS servers need to be configured with the ability to lookup any zone on the Internet, and not just locally served zones. This is generally the standard configuration of a DNS server, however you should check to make sure this is the case. DNS servers that can only look up locally served zones are not resolvers, they rely on remote DNS servers sometimes referred to as forwarders to do resolution for them.
For example, if a server wants to know what the FQDN for 1.2.3.4 is, a local resolver would look this up via DNS by connecting directly to the root DNS servers to find the authoritative DNS server for that zone. A forwarder, which is not a local resolver, would only request the FQDN from another DNS server, and that server would connect to the root DNS servers. The use of remote resolvers adds another step in the process, and causes the lookups to be considerably slower, and when remote resolvers are shared by multiple systems this can add additional delays as the remote resolver works to service requests from multiple systems.
A Local resolver is different from a remote resolver in that:
- all the software necessary to perform the lookup and to manage and present the response is installed on the server performing the lookup
- the local resolver will "talk" directly to the Internets root DNS servers. This reduces the number of steps needed to do the lookup, which is orders of magnitude faster than remote resolvers
- the local resolver is only serving requests for its server, reducing the work load and decreasing response teimes
- the local resolver also has the advantage of caching responses locally. So if an address is resolved, remote queries are not necessary for that address until the answer expires from the cache. This causes future lookups to occur instantly.
