Configure Network Services - MCSA Windows Server 2012 R2: Installation and Configuration Study Guide - page 88

Mail Exchanger Record

The mail exchanger (MX) record is used to specify which servers accept mail for this
domain. Each MX record contains two parameters—a preference and a mail server, as
shown in the following example:

domain IN MX preference mailserver_host

The MX record uses the preference value to specify which server should be used if more
than one MX record is present. The preference value is a number. The lower the number,
the more preferred the server. Here's an example:

example.com. IN MX 0 mail.example.com.
example.com. IN MX 10 backupmail.example.com.

In the example, mail.example.com is the default mail server for the domain. If that
server goes down for any reason, emailers then use the backupmail.example.com mail
server.

Service (SRV) Record

Windows Server 2012 R2 depends on some other services, like the Lightweight Directory
Access Protocol (LDAP) and Kerberos. Using a service record, which is another type of
DNS record, a Windows 2000, XP, Vista, Windows 7, Windows 8, and all Windows
Server products can query DNS servers for the location of a domain controller. This makes
it much easier (for both the client and the administrator) to manage and distribute logon
traffic in large-scale networks. For this approach to work, Microsoft has to have some way
to register the presence of a service in DNS. Enter the service (SRV) record.
Service (SRV) records tie together the location of a service (like a domain controller)
with information about how to contact the service. SRV records provide seven items of
information. Let's review an example to help clarify this powerful concept. (Table 2.4
explains the fields in the following example.)

ldap.tcp.example.com. 86400 IN SRV 10 100 389 hsv.example.com
ldap.tcp.example.com. 86400 IN SRV 20 100 389 msy.example.com

Table 2.4 The SRV record structure

Field Meaning

Domain for which this record is valid ( ldap.tcp.example.com. ).

Domain name

TTL Time to live (86,400 seconds).

This field is always IN , which stands for Internet. Class