Domain

The fully qualified domain name (FQDN) for the domain to which this resource record applies.

Service

The universal symbolic name of the TCP/IP service, such as "_telnet" or "_smtp" to be served by this record.

Protocol

The transport protocol that is used by this service. In most cases, this value is either Transmission Control Protocol (TCP) or User Datagram Protocol (UDP), although other transport protocols can be used if they are implemented for your network.

Priority

A number between 0 and 65535 that indicates the priority or level of preference given for this record to the host that is specified in Host offering this service.

Priority indicates this host’s priority with respect to the other hosts in this domain that offer the same service and are specified by different service location (SRV) resource records. Lower numbers are given higher preference. The highest priority or preference goes to a host (offering the service that is specified in this record) that has a priority value of zero (0).

Where more than one service location (SRV) resource record is present for a specific service, the host with the lowest preference number is given first to Domain Name System (DNS) clients. If this host fails or is not reachable, the SRV-specified host with the next highest preference number is the next host that is used.

If two or more hosts that are listed in the service location (SRV) resource record for a specified service share the same preference number, DNS clients can try hosts of equal preference in random order.

Weight

A number between 1 and 65535 to be used as a load-balancing mechanism. When you select among more than one target SRV host for the type of service (specified in Service) that use the same Priority number, you can use this field to weight preference toward specific hosts. Where several hosts share equal priority, SRV-specified hosts with higher weight values that are entered here should be returned first to resolver clients in SRV query results.

We recommend that you use a value of 0 (no weighting) when load-balancing is not needed. This reduces processing time for SRV queries and makes SRV resource records more readable.

Port number

The TCP/IP server port on the host that offers the service that is specified in Service on the target host that is specified in Host offering this service. The range of port numbers is 0 through 65535. This number is often—but not required to be—a well-known reserved port number as specified in Requests for Comments (RFC) 1700, "Assigned Numbers." Depending on the value in Protocol that is included in this record, the port number can represent either a UDP or TCP port.

Host offering this service

The FQDN of the target host that provides the type of TCP/IP-based service that is described in Service. This name must match a valid host (A) resource record in the DNS domain namespace. If a target FQDN consisting of a single period (".") is used here, it indicates to any DNS resolvers (clients) requesting this type of service that this service is not available for this domain.

Allow any authenticated user to update all DNS records with the same name. This setting applies only to DNS records for a new name.

When this option is selected, it permits the resource record to be updated dynamically. When the update is performed, the host requesting the update is granted permission to modify the resource record, but all other nonadministrative permissions are removed from the access control list (ACL) that protects the resource record. This makes it possible for the administrator to create a secure resource record for a host that is not yet online and still enable the resource record to be updated dynamically when the host obtains its IP address through Dynamic Host Configuration Protocol (DHCP).