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Collaboration, Voice & AV · Intermediate

Domain Name System Service Record (DNS SRV)

A DNS record type that maps a service and protocol to the hostname, port, priority and weight of servers that provide it.

Definition

Collaboration systems rely heavily on SRV records: _cisco-uds._tcp for internal CUCM discovery, _collab-edge._tls for MRA, _sip._tcp and _sips._tcp for SIP routing between domains, and _xmpp-server._tcp for federation. Priority selects preferred servers, and weight load-balances among equal priorities. Microsoft Teams uses DNS records such as _sipfederationtls._tcp for some federation scenarios.

Example

_sips._tcp.example.com SRV 10 50 5061 expe1.example.com directs secure SIP traffic to Expressway-E.

Exam tip

Lower SRV priority is preferred; weight only matters among records with equal priority.

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