What Is a Caching DNS Server?
The domain name system is an essential part of the Internet. DNS eliminates the obvious hassle of memorizing every website's IP address, the complex resolution process involves many DNS servers. For instance, a caching DNS server speeds up the resolution process for domain names you have already visited recently in the past. In this article, learn what a caching DNS server is, how it works, and the benefits of using one.
What is a caching DNS server?
A caching DNS server is a type of server that temporarily stores DNS query results to speed up subsequent requests for the same domains. It saves previously resolved domain name records in its memory. This process is called DNS caching.
Essentially, when you try to look up a website by its hostname, your computer contacts a DNS server to resolve the site’s name into an IP address. The problem is that this request won’t be completed until the domain name is converted into an IP address.
The goal of a caching DNS server, also called a DNS caching resolver, is to store the response locally in the DNS cache up until the TTL (Time-To-Live) expires. Once the information saves to the cache memory, the next time you request the same domain, the result arrives instantaneously.
This implies there’s no need to query authoritative DNS servers repeatedly for the same data. Caching servers is more beneficial from a client’s perspective. They make the DNS system more efficient and accessible for clients.
There are two types of caching DNS servers: recursive DNS servers, which perform the entire DNS resolution on behalf of the client and cache the results, and authoritative DNS servers, which are responsible for authoritative DNS records for specific domains.
Distinct from traditional DNS servers, caching servers provide information for a much wider range of domains while handling frequent requests quickly. They ultimately reduce the overall traffic on authoritative DNS servers following fast responses to queries.
Properties of caching DNS servers
Identifying a caching DNS server can come down to three primary properties: access to public DNS data, the ability to serve data to simple clients, and maintenance of a recently requested data cache.
Caching DNS servers have access to the entire range of public DNS data. The caching DNS server can access all publicly available domain name information because it knows how to navigate the global DNS hierarchy. It starts with knowledge of the root DNS servers and can follow referrals to find the correct authoritative server for the domain.
They also have the ability to serve data to simple clients. Most modern devices rely on simple DNS clients, known as "stub resolvers," to handle DNS queries. These clients don't perform the full DNS resolution process themselves.
Instead, they send a query to a more capable server and expect a complete answer in return. A caching DNS server can handle these requests by performing the necessary steps to resolve the domain name fully.
Finally, these servers maintain a cache of recently requested data. One of the key benefits of a caching DNS server is its ability to "cache," the results of recent DNS queries. When a client requests a domain name, the caching DNS server checks its cache first. If the server already cached the requested data, the server can respond much more quickly than if it had to retrieve the data from scratch.
How do caching DNS servers work?
The DNS cache concept emerged in an effort to save time and reduce traffic on the Internet. This system permits the Internet service provider (ISP) to cache DNS resolution requests for a set time frame on its DNS server. The cached information is referred to as the DNS cache.
Here’s how a DNS cache server works.
- The client sends a DNS query. When a client, like a web browser, requests to resolve a domain name, the request travels to a caching DNS server or resolver.
- The resolver performs a cache check. The DNS resolver first checks its cache to see if it already has the DNS records for the requested domain name. If the cache has the record, the client receives it immediately.
- The resolver queries upstream. If the resolver can't find the record, the DNS resolver will query upstream servers, such as the root DNS servers, then the top-level domain servers, and finally the authoritative DNS server for the domain, to resolve the domain name.
- The resolver caches the result. Once the DNS resolver obtains the DNS records from the authoritative server, it caches this information for a limited amount of time. This allows future queries for the same domain to be resolved more quickly.
One scenario involves a high-traffic website. A caching DNS server reduces the strain on the authoritative server by handling repeated queries locally.
What is a DNS cache?
A DNS cache is a temporary memory of all queries made to a DNS server from your browser. Records of all the recent visits, including A records for IPv4 addresses and AAAA records for IPv6 addresses, are contained here.
When you search a website, the database saves its IP address inside for later use. Even attempted visits to websites go into the database. Essentially, the information stored in the memory is about previous DNS lookups on a machine's operating system.
The device can automatically refer to the DNS cache when the user asks a web browser to load those websites. It will look up the domain name before issuing a request to the outside network.
A DNS cache keeps these records as long as they are valid. Each DNS record has a TTL value, which determines how long it should be cached.
Once the TTL expires, the cached record is discarded, and a fresh query is made to an authoritative DNS server when the domain is requested next round.
We need a DNS cache to improve the speed of Internet browsing. Without it, every DNS query would need to travel through the entire DNS hierarchy to finally get the answer. It would start at the root DNS servers and working its way down to the authoritative name server for the domain.
What is DNS caching?
DNS caching is the process of temporarily storing DNS query results in a cache, either on a client device, a local server, or a dedicated caching DNS server. Caching reduces the time it takes to resolve domain names.
Initially, the process involves querying authoritative DNS servers that store the necessary records. But these servers are limited in number and handle a massive volume of requests daily.
If every DNS query had to reach an authoritative server, the process would slow down. The servers could become overloaded in the long run.
By caching the information about IP addresses associated with domain names at various points in the network, you retrieve websites more quickly.
DNS caching can occur at multiple levels within the network infrastructure, including on:
- Local device caches. Each operating system has a built-in DNS resolver that stores cached DNS records. If you revisit the site, the cached result is used instead of querying a DNS server.
- Router caches. Home routers have their own DNS caching mechanisms. When a device on the network requests a DNS resolution, the router caches the response. All devices connected to the router can benefit from the cached DNS records.
- ISP DNS servers. Internet vendors operate DNS servers that cache results for their customers. When multiple users request the same domain, the ISP's DNS server responds quickly from its cache.
- Authoritative DNS servers. Even authoritative DNS servers can cache DNS records for their domains. These accelerate repeated queries for the same domain.
The benefit of DNS caching is that it updates periodically when the DNS TTL expires. Your operating system can still navigate to the website without the help of DNS resolution.
Benefits of using a caching DNS server
Using a caching DNS server offers several benefits to a user. From accelerated response times to decreased bandwidth consumption, consider the advantages to using this server.
Accelerated response times
A caching DNS server improves website loading times while surfing around the web. Because the data stays directly in its cache memory, the server helps bypass the need to query the authoritative server again. In corporate networks, it fastens resolutions.
Enhanced online security
The server contributes to online security by mitigating the impact of certain types of cyber attacks. For instance, during a DDoS attack, a caching DNS server can provide quick responses from its cache.
Again, the exposure to potential DNS spoofing attacks is minimized, as fewer queries are sent out to potentially compromised servers.
Decreased bandwidth consumption
It reduces the need to send these queries across the network to external DNS servers. This reduction in traffic conserves bandwidth, particularly in environments with few network resources.
Better user experience
Faster response times from cache servers lead to a seamless user experience. Users enjoy quicker access to the websites they are seeking, and the reduction in DNS-related delays enhances overall satisfaction with Internet services.
Configuration options for a caching DNS server
Proper configuration of a caching DNS server targets to improve three aspects: optimal performance, security, and compatibility with other network components.
Ensure that you properly set up cache memory and expiration policies. This is all about how much data the server should store. Larger caches can store more DNS records but require more memory. Smaller caches might fill up quickly, leading to more frequent cache evictions.
TTL values help set expiration policies. While it’s possible to override these values, respect the TTL set by those who are responsible for maintaining authoritative servers.
Additionally, configure cache invalidation and updates. Cache invalidation involves removing outdated DNS records from the cache when necessary. The process can be automated by setting rules based on specific conditions, such as TTL expiration or changes in DNS records. The cache should populated with fresh data.
A caching DNS server can also integrate with other caching mechanisms like content delivery networks (CDNs) or browser caching to create a multi-layered caching strategy. CDNs, for example, cache website content closer to the user, reducing load times even further.
Best practices for implementing a caching DNS server
Implementing a caching DNS server requires adherence to best practices to achieve the desired benefits. Follow these practices in order to properly implement caching servers.
- Choose the right caching strategy. Short TTLs ensure DNS records are up-to-date but can increase the number of external queries. Longer TTLs reduce the load on external servers but risk serving outdated data. So, consider the nature of the cached DNS records.
- Optimize cache size and expiration. Regularly monitor cache usage and adjust the size as needed. An overly large cache can consume excessive resources.
- Monitor cache security. The caching DNS server ought to be configured correctly to prevent DNS cache poisoning. You’re recommended to implement DNSSEC to verify the authenticity of DNS data.
- Ensure compatibility with other network infrastructure. Beyond compatibility with other components, the server’s cache settings should not conflict with those of client devices in your network.
Frequently asked questions
What is the difference between a caching DNS server and a traditional DNS server?
A caching DNS server stores DNS query results temporarily, while a traditional DNS server queries external servers directly.
How does a caching DNS server improve website loading times?
It reduces repeated queries by retrieving DNS records from the local cache instantly.
What is the problem with DNS cache?
It can cause issues if the cached information becomes corrupt or outdated.
