DNS: Service Records Basics

Introduction

This article handles Service Records in DNS without going into complete details. After reading this article you all will have a basic understating  about why DNS creates these service records (see in Figure 1) automatically inside a forward lookup zone.

 

Figure 1

 

As we all know that in our domain environment we have Sites and Services (logical in AD) and we configure them as per our physical network/subnet between different sites and accordingly our DNS creates Service records for these sites for machines to know that which server they need to contact in case if they want to contact the services which are mostly provided by a domain controller.

 

There are multiple service records inside the forward lookup zone which are required by the machines (as mentioned in Figure 1) on network because these machines need to contact variety of Active Directory Services. These records serves as the service records for machines and provide them a way to locate the way where these services exist (on which server or domain controller). These SRV records are like a Host A record however they just not only identify the server where a service exist but also what service exist on that server. In case if a machine which resides in DEN site (See Figure 2) looking for Kerberos service, should check _sites container because it contains the records of servers on which Kerberos service exist for that particular site and accordingly machine can contact any of them (in case of more than one server):

 

Figure 2

 

There is also a concept of Priority and Weight and we can priorities a server in case if there are more than one server in a particular site which cater the request for services which are same like LDAP, GC and Kerberos etc.

 

Priority and Weight can be set by Right Clicking on the service record itself (see Figure 3) and among all the servers whichever server  has a Lower Value set in Priority and a Higher Value set in Weight would be contacted first by the machines in that particular site:

 

Figure 3

Administrator can priorities a server in case if a particular server has more resources available than other servers in a site and they think that making a priority is good for their environment.

 

TIP: In case of accidental deletion of these records you can run below commands (see Figure 4) in CMD (elevated mode) and it will fix the issue for you.

 

Figure 4

Hope this article will add value to your knowledge about service records.