| Lesson 8 || Caching-only name servers |
| Objective || Describe the Purpose and Usefulness of Caching-only Name Servers |
Purpose and Usefulness of Caching-only Name Servers
A caching-only name server is a name server process with no authoritative information of its own.
Instead, it relies entirely on information obtained by recursion.
Because name servers cache the results of recursive queries for a while, a caching server will, over time, build up a substantial amount of DNS information.
The purpose of using a caching-only server is to eliminate some of the network traffic generated by the steps in the example above.
Suppose that a host is running a caching-only name server process, and the resolver library on that machine is directed to consult that local name server process.
This process does not require network access (the two processes will use UNIX interprocess communication).
If the resolver library is making a new query, the caching-only server will need to use recursion to find the answer; but subsequent requests for that information can be satisfied using the cached information.
Thus, caching eliminates a substantial amount of network traffic.
The usefulness of caching servers is particularly striking on machines running Web browers.
A typical Web page contains multiple links to the same machine, so that a user moving through a Web page generates multiple DNS queries asking about the same target.
If the local name server satisfies these requests (after the first one) without using the network, the user will get much better performance.
If your workstations connected to internet and using internet services, and if your DNS server is outside your network, the name resolution requests can take more time.
If you have a caching-only name server in your network, these name resolution queries are stored locally,
so that again if you have a name resolution query from any of you network client for the same host resolved before, you can save significant time.
The following RPMs need to be installed on the Linux computer, which is going to function as caching-only nameserver.
- bind (includes DNS server, named)
- bind-utils (utilities for querying DNS servers about host information)
- bind-libs (libraries used by the bind server and utils package)
- bind-chroot (tree of files which can be used as a chroot jail for bind)
- caching-nameserver (config files for a simple caching nameserver)
The default configuration file for the caching-only name server is /etc/named.caching-nameserver.conf . A sample /etc/named.caching-nameserver.conf configuration file is copied below.
Name Servers - Quiz
Click the Quiz link below to take a brief multiple-choice quiz on name servers.
Name Servers - Quiz