The Domain Name System (DNS) exists to translate human-readable domain names into IP addresses that computers use to communicate. At the center of that process is the A record, one of the most fundamental DNS record types. Every time someone loads a website, DNS resolution happens first. If that resolution fails, nothing else works.
A record misconfigurations are one of the most common causes of unexpected downtime during website migrations and infrastructure changes.
Understanding how A records work is essential for understanding how browsers locate servers, how root domains are configured and why DNS resolution is different from HTTP redirects.
What is an A record?
An A record, short for “Address record,” maps a hostname directly to an IPv4 address. When someone enters a domain name into a browser, the browser queries DNS to determine where that domain lives. If the domain has an A record, DNS returns the corresponding IP address.
For example, the apex (root) domain might have an A record like this:
hubspot.com → 104.17.91.187
This means that when DNS is asked for hubspot.com, it returns the IPv4 address 104.17.91.187. The browser then connects directly to that IP address to request the website.
Subdomains can also use A records. For example, a blog hosted on a separate server might use:
blog.hubspot.com → 172.64.154.108
In this case, DNS resolves blog.hubspot.com directly to the IP address 172.64.154.108, allowing the browser to connect to the server hosting the blog.
Unlike some other DNS record types, an A record does not point to another hostname. It resolves straight to an IP address. There is no aliasing and no additional DNS lookup required beyond retrieving the record itself.
How an A record works in practice
When a user types a domain into a browser, several steps occur before any webpage loads. First, the browser queries DNS to find the IP address associated with the domain. If an A record exists, DNS responds with the IPv4 address defined in that record.
The browser then connects to that IP address and sends an HTTP request for the requested hostname. At this point, web server logic and application behavior take over.
It is important to note that this DNS resolution happens before any HTTP request is made. The A record simply tells the browser where to connect. It does not control redirects, content or application logic.
A record vs AAAA record
An A record maps a hostname to an IPv4 address. An AAAA record performs the same function but maps to an IPv6 address instead. As IPv6 adoption increases, many domains publish both A and AAAA records.
When both exist, modern systems may prefer IPv6 if available. From a configuration standpoint, however, the concept is the same: both A and AAAA records enable DNS to resolve a hostname directly to an IP address.
A record vs CNAME record
A records and CNAME records are both part of DNS, but they serve different purposes.
An A record maps a hostname directly to an IPv4 address. When DNS resolves the hostname, it returns that IP address immediately.
A CNAME record maps one hostname to another hostname. The DNS must then resolve that second hostname before returning the final IP address.
An example of an A record would look like:
example.com → A → 203.0.113.10
An example of a CNAME record would look like:
blog.example.com → CNAME → hosting.example.net
hosting.example.net → A → 76.223.34.124
In this case:
- example.com resolves directly to an IP address using an A record.
- blog.example.com points to another hostname using a CNAME record.
- DNS must then resolve that hostname to determine the final IP address.
Where A records are commonly used
A records are commonly used when a hostname should resolve directly to a known IPv4 address. This often occurs when:
- Mapping a domain to a specific server or load balancer.
- Connecting infrastructure to a fixed IP endpoint.
- Configuring apex (root) domains such as example.com.
Root domains frequently use A records because traditional DNS rules do not allow a CNAME at the apex of a domain. As a result, apex domains typically resolve through A or AAAA records.
Where CNAME records are commonly used
CNAME records are useful when one hostname should alias another hostname rather than resolve directly to an IP address. This is common for:
- Subdomains managed by external services.
- CDN endpoints.
- SaaS integrations that manage their own infrastructure.
Because the CNAME points to another hostname rather than an IP address, the service provider can change the underlying infrastructure without requiring DNS changes on your domain.
Common misconceptions about A records
One common misunderstanding is that an A record performs a redirect. It does not. DNS resolution only determines which IP address a browser should connect to. Once the browser reaches the destination server, that server may return an HTTP response such as a 301 or 302 redirect. In other words, DNS decides where the request goes, while redirects determine what happens after the request arrives.
Another misconception is that DNS record choices directly influence SEO rankings. Search engines do not rank pages based on how a domain resolves in DNS. What matters is whether the site resolves reliably, loads quickly and returns correct HTTP responses.
It is also common to assume that only one A record can exist per hostname. In reality, multiple A records can be configured for the same hostname, often as a simple form of load distribution. In this case, DNS may return multiple IP addresses and the client selects one.
Common mistakes when configuring A records
Even though A records are conceptually simple, misconfigurations are common in production environments. Because DNS sits at the foundation of every web request, small mistakes can have a large impact.
Because every web request begins with DNS resolution, A record accuracy is critical. Careful planning, TTL management and post-change validation help prevent avoidable outages and inconsistent behavior.
Below are the most frequent issues teams encounter when managing A records.
1. Forgetting to update the A record after an IP change
An A record maps directly to an IP address. Because IP addresses are often tied to specific infrastructures, changes such as a server migration, infrastructure upgrade or hosting transition typically require updating the A record to point to the new IP address.
A common failure scenario occurs when an application is successfully moved to a new server, but DNS is left pointing to the old IP address. Users may reach outdated content if the old server is still active, encounter connection errors or experience inconsistent behavior depending on how traffic is routed. Because DNS operates independently from application deployment, it must be explicitly updated during infrastructure changes.
2. Ignoring TTL before making changes
TTL (Time to Live) determines how long DNS resolvers cache a record before checking for updates. If an A record has a high TTL and you change the IP address, some users may continue resolving the old IP for hours or longer.
Experienced teams typically lower the TTL 24-48 hours before a planned migration. This reduces propagation delays during cutover and minimizes the window of inconsistent resolution. Failing to account for TTL often leads to confusion when some users see the new server while others continue hitting the old one.
3. Confusing DNS changes with redirect behavior
An A record does not perform redirects. It does not modify URLs, enforce HTTPS or control canonical behavior. It simply tells the browser which IP address to connect to.
When unexpected behavior occurs after updating an A record, administrators sometimes assume the DNS change caused a redirect or routing issue. In reality, redirects occur at the HTTP layer after the browser resolves DNS.
4. Accidentally creating conflicting A records
Multiple A records for the same hostname can be used intentionally for basic load distribution. However, unintentional duplication can cause inconsistent behavior.
If different A records point to servers with mismatched configurations, users may experience intermittent errors depending on which IP their resolver selects. This can make debugging especially difficult because the issue may not reproduce consistently across locations or devices. When using multiple A records, the infrastructure behind each IP must be synchronized.
5. Failing to align DNS with server configuration
Pointing an A record to a new IP address is only part of the process. The destination server must be properly configured to accept traffic for the hostname.
Common oversights include missing SSL certificates, incorrect virtual host configuration or firewall rules that block incoming traffic. In these cases, DNS resolves correctly, but the connection fails or produces certificate warnings. DNS and server configuration must be aligned for the site to function properly.
6. Leaving stale A records in place
Infrastructure changes over time. Old servers are decommissioned, hosting providers change and services are consolidated. If unused A records are left in DNS, they can create confusion during troubleshooting or future migrations.
This is especially important when multiple A records are used for DNS round-robin load balancing. When several A records exist for the same hostname, DNS may return all of them and clients will typically attempt one of the IPs. If one of those IP addresses is stale or no longer active, some users may be routed to a non-functional server or old content while others reach the correct one.
Because of this, stale records can introduce intermittent failures, inconsistent routing and difficult-to-diagnose outages. Periodic DNS audits help ensure that all A records represent active infrastructure and that load balancing configurations only include valid endpoints.
A records and redirects
A records and redirects operate at different layers of the request process. DNS resolution happens first and determines which server should resolve a request. The server may then redirect the request if the desired resource has been moved to a different URL.
In short, an A record maps a domain name to an IP address, routing traffic to the correct server. That sever can then return a redirect at the HTTP layer.
For example:
- A domain’s A record points to the server IP 203.0.113.10.
- The server at that IP responds with a 301 redirect to another URL.
In this scenario, DNS does not perform the redirect, it only routes the request to the correct server, where the redirect logic is applied.
Understanding this distinction helps when troubleshooting:
- If a site does not load, the issue may be related to DNS or IP resolution.
- If a URL changes or redirects unexpectedly, the issue likely exists at the HTTP or application layer.
Final thoughts about A records
The A record is one of the simplest yet most foundational components of DNS. It maps a hostname directly to an IPv4 address, enabling browsers to locate and connect to servers. While it does not control redirects, content or SEO directly, it forms the starting point for every web request.
Understanding how A records work clarifies the broader architecture of the web. It also helps distinguish DNS behavior from application-level behavior, reducing confusion when diagnosing site issues or configuring infrastructure.
For any domain owner or infrastructure team, mastering A records is not optional. It is foundational knowledge that supports everything built on top of it.
Frequently asked questions about A records
What does an A record do?
An A record maps a domain name or subdomain directly to an IPv4 address. When someone enters a domain into a browser, DNS uses the A record to determine which IP address the browser should connect to. It does not perform a redirect or change the URL; it simply tells the browser where the server is located.
What is the difference between an A record and a CNAME record?
An A record points directly to an IP address, while a CNAME record points to another hostname. When a CNAME is used, DNS must resolve that hostname before returning the final IP address. In other words, an A record maps a domain directly to a server, while a CNAME creates an alias that references another domain.
Can I have multiple A records for one domain?
Yes, a single hostname can have multiple A records. This is often used for basic load distribution or redundancy. When multiple A records exist, DNS may return more than one IP address and the client typically selects one. This setup can help distribute traffic across multiple servers.
How long does it take for an A record to update?
The time it takes for an A record change to take effect depends on the TTL (Time to Live) setting. The TTL controls how long DNS resolvers cache the record before checking for updates. If the TTL is set to one hour, for example, changes may take up to an hour to propagate fully. Some resolvers may also cache results longer, depending on configuration.
Can an A record cause downtime?
An incorrect A record can cause downtime if it points to the wrong IP address or to a server that is not configured properly. If DNS directs traffic to an invalid or unreachable IP, users will not be able to load the website. This is why DNS updates should be validated carefully after changes.
Is an A record a redirect?
No, an A record is not a redirect. DNS resolution happens before any HTTP request is made. An A record simply provides the IP address associated with a hostname. Redirects, such as 301 or 302 responses, are handled at the HTTP layer after DNS is resolved.
What happens if an A record is missing?
If a domain does not have an A or AAAA record (or another valid resolving record), DNS cannot return an IP address. In that case, browsers will fail to connect and users may see an error indicating that the server cannot be found. Without a resolving record, the domain cannot serve web traffic.
Do A records affect SEO?
A records do not directly affect SEO. However, correct DNS configuration affects site availability and reliability, which indirectly impacts crawlability and user experience. A misconfigured A record that causes downtime can therefore negatively affect search performance.
What is the difference between an A record and an AAAA record?
An A record maps a hostname to an IPv4 address, while an AAAA record maps a hostname to an IPv6 address. Many modern websites publish both. If both are available, systems that support IPv6 may prefer the AAAA record.
By Shannon Young
Customer Success Manager
Shannon is a seasoned professional in the customer success space. She has years of experience in a wide variety of customer-facing roles in various sectors.
Always ready to take on the next challenge, whether it be a new offensive cross stitch pattern or making her dogs sit still for another themed photo, she is prepared for anything.
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