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.

Caching-only name servers, also known as caching DNS resolvers or recursive DNS resolvers, play a vital role in the Domain Name System (DNS) by improving the efficiency, performance, and reliability of domain name resolution. They do not host any authoritative DNS records themselves but rather act as an intermediary between clients and the authoritative name servers that hold the actual DNS records.
The primary purpose and usefulness of caching-only name servers can be described as follows:

1. Reduced Latency: By caching DNS query results, caching-only name servers can significantly reduce the latency associated with domain name resolution. When a client sends a DNS query, the caching-only name server checks its cache for the requested information. If the information is found in the cache and has not expired, the caching-only name server returns the cached data to the client, avoiding the need for additional queries to the root, TLD, or authoritative name servers.
2. Lowered Query Load: Caching-only name servers help lower the overall query load on the root, TLD, and authoritative name servers. By storing previously resolved query results, caching-only name servers can answer subsequent requests for the same information without querying the upstream servers, reducing the number of queries those servers need to handle.
3. Improved Resilience: In case of temporary unavailability or network issues affecting an authoritative name server, caching-only name servers can still respond to queries with cached data (provided the Time to Live, or TTL, has not expired). This feature improves the resilience of the DNS infrastructure, ensuring that domain name resolution can continue even when faced with network issues or server outages.
4. Faster Client Response: Caching-only name servers are typically configured to be geographically close to the clients they serve, resulting in faster response times for DNS queries. This proximity to clients helps to improve the overall user experience by reducing the time it takes to resolve domain names and access resources on the internet.
5. Load Balancing and Redundancy: Caching-only name servers can be deployed in clusters, providing load balancing and redundancy for DNS query handling. This setup ensures that DNS queries are distributed evenly across multiple servers and that the service remains available even if one or more servers experience downtime.

In summary, caching-only name servers are a crucial component of the DNS infrastructure, enhancing the efficiency, performance, and reliability of domain name resolution. They achieve this by caching query results, reducing latency, lowering query loads on upstream servers, and providing improved resilience, faster client response times, and load balancing and redundancy.

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.

1. bind (includes DNS server, named)
2. bind-utils (utilities for querying DNS servers about host information)
3. bind-libs (libraries used by the bind server and utils package)
4. bind-chroot (tree of files which can be used as a chroot jail for bind)
5. 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.

Click the Quiz link below to take a brief multiple-choice quiz on name servers.
Name Servers - Quiz