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SRV Record Lookup

Service (SRV) records specify the hostname and port number for specific internet services.

RFC: RFC 2782
TYPE: Service Locator
FORMAT: _service._proto.name. TTL IN SRV priority weight port target.

What is SRV Record Lookup?

Unlike A records that only provide an IP address, SRV records detail exactly *where* to find a specific service by providing a target hostname, an explicit port number, a priority, and a weight.

How it Works

Client software looking for a specific service (like LDAP, SIP, or Minecraft) requests a structured SRV record (e.g., `_sip._tcp.example.com`). The DNS server replies with the server alias and explicit port where the service is listening.

Key Use Cases

Connecting to VoIP/SIP systems, Microsoft Active Directory, or XMPP chat servers.

Directing users to specific game server ports (e.g., Minecraft servers without explicitly tying them to port 25565).

Load balancing specialized services using the Weight property.

Advanced Details

SRV records eliminate the need for users to remember numeric ports. The client application simply queries the canonical service name, and the DNS dynamically yields the exact IP and Port mapping.

Cybersecurity Pros & Cons

Security Advantages
  • SRV enumeration during recon reveals hidden internal services (LDAP, Kerberos, SIP) exposed to the internet.
  • Port information in SRV records enables precise firewall rule creation for allowed service traffic.
  • SRV record abuse detection helps identify rogue services registered inside a DNS zone.
  • Priority and weight fields allow security-aware load balancing to route traffic through monitored nodes first.
Security Limitations
  • SRV records publicly disclose internal service architecture, reducing security through obscurity posture.
  • Attackers enumerate `_kerberos._tcp` and `_ldap._tcp` SRV records to map Active Directory infrastructure.
  • Misconfigured SRV records pointing to wrong ports can silently route service traffic to unintended systems.
  • No native authentication in SRV — any server can claim a service record if DNS zone security is weak.
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