DNS Records Lync Server Uses

Lync Server utilizes DNS for several purposes. Not only do traditional hostname-to-IP address lookups occur, Lync Server utilizes specialized DNS records to identify particular services much like Active Directory does. Lync Server is even able to use DNS round robin to provide load balancing between sites. Some record examples include

• A or address records

• PTR or pointer records

• SRV or service location records

Lync Server requires registration of hostnames of servers as A records. Administrators implementing the DNS load-balancing features of Lync Server are required to specify the server FQDN and the cluster FQDN using the same IP address for each server in the cluster and A records for all clusters that contain an Enhanced registrar. For example:

The more unusual DNS records used by Lync Server are SRV records. These are used to identify resources of a particular type that are either providing a specific service or that are in a particular location. This is where the subdomains come into play. For example:

_sipinternal._tcp.companyabc.com

SRV records hold additional information, such as

Domain: Companyabc.com

Service: _sipfederationtls

Protocol: _tcp

Priority: 10

Weight: 100

Port number: 5061

Host offering this service: FQDN of host

This enables a client to ask DNS where to find a host providing a specific service, and DNS can return one or more answers. By using Priority and Weight, one can enforce a behavior of how loads are shared or directed.