Dependency of Active Directory on DNS

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DNS Records that are required for proper functionality of Active Directory

 

We know that DNS servers serves more than resolving Name to IP and IP into Name. It is core protocol or you can say daddy of all protocols over a network.

In this article I have tried to visualize and explain all the core records of DNS without which Active Directory cannot function properly.

Here are the list of all core SRV, A and C-Name records that are used by Active Directory and Domain clients.

Please Note: The Red marked records in below table are used by Non-SRV-Aware Clients

 

Mnemonic Type DNS Record Requirements
  1. PDC
SRV _ldap._tcp.pdc._msdcs.<DnsDomainName> One per domain
  1. GC
SRV _ldap._tcp.gc._msdcs.<DnsForestName> At least one per forest
  1. KDC
SRV _kerberos._tcp.dc._msdcs.<DnsDomainName> At least one per domain
  1. DC
SRV _ldap._tcp.dc._msdcs.<DnsDomainName> At least one per domain
A <DomainControllerFQDN> One per domain controller (domain controllers that have multiple IP addresses can have more than one A resource record)
  1. GcIpAddress
A gc._msdcs.<DnsForestName> At least one per forest
  1. DsaCname
CNAME <DsaGUID>._msdcs.<DnsForestName> One per domain controller

 

Below I have mentioned the location of all these important records, with their properties and NSLOOKUP commands to verify if the record exists correctly or not. I have taken screenshot from a single domain lab, on default site i.e. my domain itself represent the forest. So results may vary if you explore these in big infrastructure.

 

 

In the records Properties window, you will notice below few fields:

Priority-    The priority of the server. Clients attempt to contact the server with the lowest priority.

Weight –   A load-balancing mechanism that is used when selecting a target host from those that have the same priority. Clients randomly choose SRV records that specify target hosts to be contacted, with probability proportional to the weight

Port Number-    The port where the server is listening for this service.

Target –   The fully qualified domain name of the host computer.

 

 

 

Host Records for SRV-Aware Clients

  1. PDC Record – _ldap._tcp.pdc._msdcs.<DnsDomainName>

Allows a client to locate the server that is acting as the primary domain controller (also known as a “PDC”) in the mixed-mode domain named in DnsDomainName . Only the PDC emulator master of the domain registers this SRV record.

 

 

 

  1. GC Record – _ldap._tcp.gc._msdcs.<DnsForestName>

Allows a client to locate a Global Catalog (gc) server for this forest. Only domain controllers that are functioning as Global Catalog servers for the forest named in DnsForestName register this SRV record.

 

 

  1. KDC Record – _kerberos._tcp.dc._msdcs.<DnsDomainName>

Allows a client to locate a domain controller that is running the Windows implementation of the Kerberos KDC service for the domain named in DnsDomainName . All Windows Server–based domain controllers that are running the KDC service (that is, that implement a public key extension to the Kerberos v5 protocol Authentication Service Exchange subprotocol) register this SRV record.

 

 

  1. DC Record – _ldap._tcp.dc._msdcs.<DnsDomainName>

Allows a client to locate a domain controller (dc) of the domain named by DnsDomainName . All Windows Server–based domain controllers register this SRV record.

 

 

  1. Domain FQDN A Record  – <DomainControllerFQDN>

This record helps to locate the domain controllers IP address in a domain.

 

Host Records for Non-SRV-Aware Clients

 

  1. GC IP Address – gc._msdcs.<DnsForestName>

Allows a non-SRV-aware client to locate any Global Catalog server in the forest by looking up an A record. A name in this form is returned to the LDAP client through an LDAP referral. A non-SRV-aware client looks up this name; an SRV-aware client looks up the appropriate SRV resource record.

Net Logon also registers a DNS CNAME (alias) record for use by Active Directory replication The Locator does not use this record.

 

 

  1. DsaCname Record – <DsaGUID>._msdcs.<DnsForestName>

Allows a client to locate any domain controller in the forest by looking up an A record. The only information that is known about the domain controller is the GUID of the directory system agent (also known as the “DSA”) object for the domain controller and the name of the forest in which the domain controller is located. This record is used to facilitate renaming a domain controller.

 

To know more about SRV records in DNS , please refer to below article

http://technet.microsoft.com/en-us/library/cc961719.aspx

 

 

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AD Integrated DNS

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DNS Scenario – AD integrated DNS

Your company, Contoso Ltd has a main office and a branch office. The offices are connected by a WAN link. Contoso has an Active Directory forest that contains a single domain named ad.contoso.com.

The ad.contoso.com domain contains one domain controller named DC1 that is located in the main office. DC1 is configured as a DNS server for the ad.contoso.com DNS zone. This zone is configured as a standard

primary zone. You install a new domain controller named DC2 in the branch office. You install DNS on DC2.

You need to ensure that the DNS service can update records and resolve DNS queries in the event that a WAN link fails.

What should you do?

A. Create a new stub zone named ad.contoso.com on DC2.

B. Create a new standard secondary zone named ad.contoso.com on DC2.

C. Configure the DNS server on DC2 to forward requests to DC1.

D. Convert the ad.contoso.com zone on DC1 to an Active Directory-integrated zone.

Correct Answer: D

Explanation

An AD integrated DNS can automatically get all the updates from AD. Later these records can be transferred to secondary DNS server to avoid any downtime during WAN link issue.


AD integrated DNS and Security

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DNS Scenario – AD Integrated DNS and Security

Your network consists of a single Active Directory domain. All domain controllers run Windows Server 2008 R2 and are configured as DNS servers. A domain controller named DC1 has a standard primary zone for contoso. com. A domain controller named DC2 has a standard secondary zone for contoso.com.

You need to ensure that the replication of the contoso.com zone is encrypted. You must not lose any zone data.

What should you do?

A. Convert the primary zone into an Active Directory-integrated stub zone. Delete the secondary zone.

B. Convert the primary zone into an Active Directory-integrated zone. Delete the secondary zone.

C. Configure the zone transfer settings of the standard primary zone. Modify the Master Servers lists on the secondary zone.

D. On both servers, modify the interface that the DNS server listens on.

Correct Answer: B

Explanation:

All non-AD integrated DNS zones are saved in a text file i.e. .dns file and it is not encrypted