A Record Lookup: Finding IP Addresses for Domains
Look up A records to find the IPv4 addresses a domain resolves to. Understand what A records do, how DNS resolution works, and how to diagnose common issues.
What A Records Do
An A record maps a domain name to an IPv4 address, as defined in RFC 1035 Section 3.4.1. When a browser, mail server, or any other client needs to connect to example.com, the DNS resolver queries for an A record and gets back an address like 93.184.216.34. Without an A record (or a CNAME that eventually resolves to one), the domain has no IPv4 destination — connections fail.
A domain can have multiple A records pointing to different IP addresses. This is how DNS-based load balancing works: the resolver returns all addresses and the client picks one, distributing traffic across servers. Round-robin DNS is the simplest form, though most production setups pair it with health checking at the load balancer layer.
How DNS Resolution Works for A Records
When you query a domain, the resolver follows the delegation chain described in RFC 1034 from root to TLD to authoritative nameserver. At each step, the resolver asks "who is responsible for this zone?" until it reaches the server that holds the actual A record. The final authoritative answer includes the IPv4 address and a TTL value that controls how long resolvers cache the result.
If a CNAME record exists for the queried name, the resolver follows the alias first, then looks up the A record for the CNAME target. This adds a resolution step — and a potential point of failure if the CNAME target does not have an A record.
Common A Record Issues
Wrong IP address. The A record points to an old server after a migration. The domain resolves, but traffic goes to the wrong destination. Verify the IP matches your current hosting provider's assigned address.
Missing A record. The domain has no A record and no CNAME. Browsers show "DNS_PROBE_FINISHED_NXDOMAIN" or similar errors. This usually means the record was never created or was accidentally deleted during a DNS change.
CNAME conflict at the apex. A bare domain (example.com, no www) cannot have a CNAME alongside other record types like MX or TXT. Some DNS providers offer ALIAS or ANAME records as a workaround, which synthesize an A record from a CNAME target at query time.
Multiple A records with stale entries. If you added a second server and later decommissioned it without removing the A record, roughly half of connections will fail. Audit your A records after any infrastructure change.
A Records vs. AAAA Records
A records return IPv4 addresses (32-bit, like 93.184.216.34). AAAA records return IPv6 addresses (128-bit, like 2606:2800:220:1:248:1893:25c8:1946). Modern best practice is to publish both — a dual-stack configuration — so clients with IPv6 connectivity can use it while IPv4-only clients still work. Use the AAAA Lookup tool to check IPv6 alongside your A records.
Checking A Records
Use the mxio A Lookup to query A records for any domain and see every IPv4 address returned, along with TTL values. For a broader view of all record types on a domain, use the DNS Lookup tool.
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