Difference between revisions of "Local DNS resolver"
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Revision as of 12:21, 8 July 2013
A local DNS resolver is standard piece of software typically installed on the server performing the lookup 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.
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. DNS servers that can only look up locally served zones are not local resolvers, they rely on remote DNS servers sometimes referred to as forwarders.
For example, if a server wants to know what the FQDN for 1.2.3.4 is, it 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. This adds another step in the process, and causes the lookups to be considerably slower.
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, and 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, and 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.
