However, on the bright side, slow DNS lookups are usually easy to diagnose once you know where to look. In this guide, we’ll cover the common causes of slow DNS lookups and the steps you can take to identify and fix them.
What Causes Slow DNS Lookups?
Before fixing a slow DNS lookup, it helps to understand what can cause it in the first place.
When you enter a domain such as example.com into your browser, your device needs to find the domain’s IP address before it can connect to the server. This requires a DNS lookup. Depending on the situation, your device may check its local DNS cache first. If the answer isn't cached, the query may be sent to a recursive DNS resolver. That resolver may then need to contact other DNS servers to find the correct answer.
Several things can slow down this process, and a few of them are listed below:
Slow or Overloaded DNS Servers
The DNS resolver you're using may be experiencing high traffic, technical problems, or network congestion. Your internet service provider usually assigns a DNS resolver automatically, but you aren't necessarily limited to using it. A slow resolver can increase the time needed to resolve domains, especially if the issue occurs repeatedly.
High Network Latency
DNS queries have to travel between your device and a DNS resolver. If that resolver is geographically far away or the network connection between you and the resolver is slow, DNS queries can take longer. This can be especially noticeable on unstable Wi-Fi connections, congested networks, or connections with high latency.
Too Many DNS Lookups
Some websites require many DNS lookups before a page can fully load. For example, a website may load resources from several third-party domains, such as analytics platforms, advertising networks, content delivery networks, and external APIs.
Each additional domain may require its own DNS lookup. While DNS caching can reduce the impact, a large number of external resources can still contribute to slower page loading.
DNS Misconfiguration
Incorrect DNS records can cause lookup problems or force resolvers to make additional queries. Issues with records such as A, AAAA, CNAME, MX, and NS records can affect how quickly a domain resolves. Incorrect nameserver settings can also cause delays or failed lookups.
DNSSEC-Related Problems
DNSSEC adds a layer of authentication to DNS responses. When configured correctly, it helps protect users from certain types of DNS attacks.
However, incorrect DNSSEC configuration can cause validation problems. In some cases, resolvers may spend additional time processing a query or return an error instead of the expected DNS response.
Problems With Authoritative Nameservers
A recursive resolver eventually needs to communicate with the authoritative nameserver responsible for a domain. If that nameserver is slow, unreachable, poorly configured, or experiencing network issues, DNS resolution can also slow down.
How to Check if DNS is Actually the Problem
Before changing your DNS settings, first make sure DNS is actually causing the delay. A website taking too long to load does not always mean that DNS lookups are slow.
For example, the problem could be with the web server hosting the website, your internet connection, the browser, a database, or one of the third-party services the website uses. If you change your DNS settings without checking the actual cause, you may end up fixing something that was never broken.
This is what you should ideally do:
Start With an Online DNS Lookup
You can use an online DNS lookup tool such as Nslookup.io to check a domain's DNS records without using command-line tools. Enter the domain you're troubleshooting and run a lookup to see the DNS information associated with it.
You may see records such as A, AAAA, CNAME, MX, NS, SOA, and TXT records. Looking at these records gives you a basic picture of how the domain's DNS is configured. For slow DNS lookups, however, simply checking whether a record exists isn't enough. You also need to look at which DNS server is answering the query and how it responds.
Compare Different DNS Servers
The same domain can be queried through different DNS servers, and they may not all respond in exactly the same way. A lookup that is slow through one resolver may be much faster through another.
Try querying the same domain through different public DNS resolvers and compare the results. If one resolver consistently responds more slowly than the others, the problem could be related to that resolver or the network path between your device and the resolver.
On the other hand, if several different resolvers show similar delays for this domain while other domains resolve quickly, the problem may be further along the DNS resolution process. In that case, the domain's authoritative nameservers or DNS configuration may need closer attention. This comparison is useful because it helps you narrow down the source of the delay instead of assuming that the domain itself is responsible.
Check the Authoritative DNS Server
If several public DNS resolvers appear to be slow, the next step is to check the domain's authoritative DNS servers.
Authoritative DNS servers are responsible for providing the official DNS records for a domain. When a recursive resolver needs an answer that isn't already available in its cache, it eventually contacts the authoritative server responsible for that domain.
Checking the authoritative server can therefore help you determine whether the delay is happening at the resolver level or closer to the domain's own DNS infrastructure. If the authoritative server responds normally while one public resolver is noticeably slower, the issue may be related to that resolver or the network path between the two. If the authoritative server is also slow or frequently unavailable, the domain's DNS hosting or nameserver setup may need to be investigated.
Look at Individual DNS Records
Slow DNS resolution isn't always caused by the domain as a whole. Sometimes, a particular record or part of the DNS configuration can contribute to the problem.
For example, check the CNAME record to see whether a hostname points to another hostname. When several CNAMEs are chained together, the resolver may need to perform additional lookups before it can reach the final destination. Unnecessary or complicated CNAME chains can therefore add extra steps to DNS resolution.
You can also check A and AAAA records to see where a domain resolves for IPv4 and IPv6 connections. If you're troubleshooting email, MX records show which mail servers handle messages for the domain. NS and SOA records can provide useful information about the domain's DNS infrastructure.
Looking at these records together can help you spot missing records, unexpected CNAMEs, incorrect configurations, or other issues that may require further investigation.
Compare Results From Different Locations
DNS performance can also vary depending on where the request is coming from. A domain may resolve quickly for users in one region but take longer for users in another because of differences in DNS resolvers, network routes, or the location of the DNS infrastructure.
This is particularly useful when a website appears to be slow only for users in a specific country or region. Run the same DNS lookup from different locations and compare the responses. If the domain resolves normally in one location but slowly in another, that gives you an important clue.
The problem may not be with the DNS records themselves. It could be related to a particular resolver, network route, or regional DNS infrastructure.
Don't Forget DNS Caching
DNS responses are commonly cached to avoid repeating the same lookup every time someone visits a domain. While caching improves performance, it can also make DNS troubleshooting a little confusing.
So, if you recently changed a DNS record, different DNS resolvers may continue returning the old information until their cached records expire. This is controlled by the record's TTL (Time to Live). As a result, seeing an older DNS record doesn't necessarily mean that your recent change failed. Check the domain through multiple DNS servers and give cached responses enough time to expire.
Keep in mind that an online DNS lookup tool may not cache the results it displays, but the DNS servers being queried can still have cached information.
By comparing different DNS servers, checking authoritative nameservers, reviewing individual records, and testing from different locations, you can get a much clearer picture of where a slow DNS lookup is coming from. From there, you can decide whether you need to change your DNS resolver, review your DNS configuration, investigate your authoritative nameservers, or look for a problem outside DNS altogether.
How to Fix Slow DNS Lookups
Once you've confirmed that DNS is contributing to the delay, you can start looking for the cause. The right fix depends on where the problem is happening, so it's better to work through these steps one at a time rather than changing several DNS settings at once.
Try a Different DNS Resolver
If your current DNS resolver is slow, switching to another reliable resolver may improve lookup performance. Public DNS services such as Google Public DNS, Cloudflare DNS, and Quad9 are commonly used alternatives and can be tested against your current resolver.
Don't switch immediately, though. First, compare how quickly different resolvers respond to the same domain. If another resolver consistently responds faster and provides reliable results, changing your DNS settings may help reduce lookup delays.
Restart Your Router and Network Connection
Sometimes, slow DNS lookups are caused by a temporary network problem rather than a problem with DNS itself. Restarting your router can clear certain temporary connection issues and give your network connection a fresh start.
After restarting, reconnect your device and run the DNS test again. If DNS queries are still slow across multiple devices on the same network, the problem could be related to your router, internet service provider, or DNS resolver rather than one particular device.
Check Your DNS Records
If you're troubleshooting a domain you manage, review its DNS records carefully. Look for incorrect or missing A and AAAA records, unnecessary CNAME chains, incorrect nameserver records, incorrect MX records, DNSSEC configuration errors, or authoritative nameservers that aren't responding properly.
Pay particular attention to long CNAME chains. If one hostname points to another, which points to another, the resolver may need to perform several additional steps before reaching the final destination. Removing unnecessary DNS dependencies can make the configuration simpler and easier to resolve.
Reduce Unnecessary Third-Party Domains
If you're troubleshooting a slow website, check how many external services it depends on. Scripts, images, fonts, analytics platforms, APIs, advertising services, and other third-party resources may all require DNS lookups before they can load.
A website that depends on dozens of external domains can therefore generate many DNS requests. Review these resources and remove anything that isn't necessary. Reducing unused third-party services can lower the number of DNS lookups and may improve the website's overall loading performance.
Check Authoritative DNS Server Performance
If a domain is slow to resolve through several different DNS resolvers, the problem may be closer to its authoritative DNS infrastructure. Authoritative nameservers provide the official DNS records for a domain, so their performance can affect how quickly those records are retrieved.
Check which nameservers are authoritative for the domain and see whether they respond consistently. If multiple public DNS resolvers show similar delays when querying the same domain, that is a useful clue that the problem may not be limited to one recursive resolver.
Check for Network Latency
DNS queries travel across a network between your device and the DNS resolver. If that connection has high latency, congestion, or routing problems, DNS responses may take longer than expected.
You can use tools such as ping and traceroute on macOS or Linux, or tracert on Windows, to investigate network connectivity and latency. Keep in mind that some DNS servers block or deprioritize ICMP traffic, so a failed ping does not automatically mean the DNS server is unavailable. Use these tests alongside actual DNS query results.
Give DNS Changes Time to Propagate
If you've recently changed DNS records or nameservers, don't expect every DNS resolver to show the new information immediately. DNS records have a TTL value that tells resolvers how long they can cache a response.
Because of caching, different DNS resolvers may temporarily return different results after a change. Your device may still receive an older response while another resolver has already picked up the new record. When troubleshooting recent DNS changes, check the domain through multiple resolvers and allow enough time for cached responses to expire.
Final Thoughts on Keeping DNS Lookups Fast and Reliable
As your website grows, your DNS setup can become more complex. New services, subdomains, third-party tools, and DNS changes can all affect how your domain resolves. That makes it worth checking your DNS from time to time instead of waiting for users to report a problem.
Regular DNS checks can help you spot unusual records, slow responses, or configuration changes early. They can also give you a better idea of how your domain looks to users in different locations.
Ready to take a closer look? Enter your domain in Nslookup.io to check your DNS records and see how your domain is resolving.