BRev SRV record — service locator
SRV is the only common DNS record that carries a port number, which is its whole reason to exist: it says “the service _sip over _tcp for this domain runs on that host, at that port”. Everything else in DNS gets you to a machine and leaves the port to convention.
The name encodes the service and transport with leading underscores — _service._proto.name — and the underscores are deliberate, because they cannot appear in a normal hostname and so cannot collide with one. The RDATA then carries four fields: priority (lower is tried first, like MX), weight (proportional share among equal priorities), port, and target hostname.
Priority and weight are frequently confused. Priority picks the tier: all priority-10 targets are tried before any priority-20 target. Weight distributes traffic within a tier proportionally — two targets at weight 30 and 70 get roughly 30% and 70%. In practice SRV is what makes Microsoft 365 and XMPP autodiscovery work, how Active Directory clients find domain controllers, and the trick that lets a Minecraft server run on a non-default port without players typing it.
What a SRV record looks like
Type 33 · Service locator (priority weight port target). Zone-file form below — owner name, TTL, then the record and its RDATA.
| Name | TTL | Record | What it means |
|---|---|---|---|
| _sip._tcp.example.com. | 3600 | SRV 10 60 5060 sip1.example.com. | priority 10, weight 60, port 5060 — the preferred SIP server, taking 60% of the tier. |
| _sip._tcp.example.com. | 3600 | SRV 10 40 5060 sip2.example.com. | Same priority, weight 40 — the other 40% of traffic in that tier. |
| _sip._tcp.example.com. | 3600 | SRV 20 0 5060 sip-dr.example.com. | Priority 20: only used when every priority-10 target is unreachable. |
| _minecraft._tcp.example.com. | 3600 | SRV 0 5 25599 mc.example.com. | The Minecraft trick: players type example.com and the client finds the non-default port. |
The mistakes that break production
Forgetting the underscores or the trailing dot
The name must be exactly _service._proto.domain, and the target must be a fully-qualified hostname (with the trailing dot in a zone file). Control panels vary in whether they append the zone for you, which is how targets end up as mc.example.com.example.com — query the record and read what was actually published.
Pointing the SRV target at a CNAME
The target should resolve directly via A/AAAA records. Some clients follow a CNAME and some do not, so the result is a service that works for part of your users. Same rule as MX, and same confusing symptom.
Query a SRV record now
The box below is seeded with _sip._tcp.example.com. Choose SRV as the type and press Look up — the query goes from your browser straight to Cloudflare or Google over DNS-over-HTTPS, with no server of ours in the path.
DNS is the internet's address book: it turns a name like example.com into the addresses and service endpoints machines actually connect to. Every record has a type (what kind of fact it states) and a TTL (how long resolvers may cache it).
Record types
| Type | What it stores |
|---|---|
| A | IPv4 address |
| AAAA | IPv6 address |
| CNAME | Canonical name (alias) |
| MX | Mail exchanger (priority target) |
| TXT | Text — SPF, verifications, DKIM, arbitrary data |
| NS | Authoritative nameservers |
| SOA | Start of authority (serial, refresh, retry, expire, minimum) |
| SRV | Service locator (priority weight port target) |
| CAA | Which CAs may issue certificates |
| PTR | Reverse DNS (IP → name) |
| DNSKEY | DNSSEC public key |
| DS | Delegation signer (DNSSEC chain of trust) |
| HTTPS | HTTPS service binding (ALPN, ECH, hints) |
| SVCB | General service binding |
| TLSA | DANE — pin certificates in DNS |
| NAPTR | Name authority pointer (SIP/ENUM) |
TTL & “propagation”
DNS changes don't “push” anywhere — resolvers simply keep the old answer until its TTL runs out, then fetch the new one. So a change “propagates” in at most the old record's TTL. Planning a change? Lower the TTL (e.g. to 300s) a day in advance, make the change, then raise it back. The compare card above shows whether major public caches have picked your change up yet.
FAQ
What is the difference between priority and weight in an SRV record?
Priority selects the tier — everything at the lowest priority is tried first. Weight distributes load proportionally among targets that share a priority, so weight only matters within a tier.
What uses SRV records?
Microsoft 365 and Exchange autodiscovery, XMPP, SIP, Active Directory domain controller location, Kerberos, LDAP and Minecraft Java Edition, among others. Web browsers do not use SRV — that is what HTTPS and SVCB records are for.
Can an SRV record point to a different port?
Yes — that is the point of the type. It is the only widely deployed record that carries a port, which is why it lets a service run somewhere other than its default without every client being reconfigured.