MCTS Guide to Configuring Microsoft Windows Server 2008 Active Directory Chapter 9: Configuring DNS for Active Directory
Objectives Describe the structure of Domain Name System Install and use the DNS Server role in Windows Server 2008 Configure DNS zones Configure advanced DNS server settings Monitor and troubleshoot DNS MCTS Windows Server 2008 Active Directory 2
Introduction to Domain Name System Domain Name System (DNS) is a distributed hierarchical database composed mainly of computer name and IP address pairs In order to resolve a name to an address, a DNS lookup will often require multiple queries to a hierarchy of DNS servers MCTS Windows Server 2008 Active Directory 3
The Structure of DNS DNS can be described as an inverted tree structure Entire DNS tree is called the DNS namespace Each domain has one or more servers that are authoritative for the domain Root servers keep a database of addresses of other DNS servers managing top-level domain names, called top-level domain (TLD) servers MCTS Windows Server 2008 Active Directory 4
The Structure of DNS (cont.) MCTS Windows Server 2008 Active Directory 5
The DNS Database A zone is a grouping of DNS information that represents one or more domains and possibly subdomains Zones contain a variety of record types called resource records, which contain information about network resources DNS records can be added and changed by: Static updates Dynamic updates MCTS Windows Server 2008 Active Directory 6
The DNS Database (cont.) DNS resource record types MCTS Windows Server 2008 Active Directory 7
The DNS Lookup Process Two different types of DNS lookup can be performed Iterative query A DNS server will respond with the best information it has to satisfy the query, or it may give a referral response Recursive query DNS server processes the query until it responds with an address that satisfies the query or with an I don t know message A typical DNS lookup made by a DNS client can involve both recursive and iterative queries DNS clients maintain a Hosts file that can contain static DNS entries; Hosts is stored in %systemroot%\system32\drivers\etc MCTS Windows Server 2008 Active Directory 8
The DNS Lookup Process (cont.) MCTS Windows Server 2008 Active Directory 9
DNS Server Roles DNS servers can perform one or more of the following roles for a zone: Authoritative server Holds a complete copy of a zone s resource records Forwarder A DNS server to which other DNS servers send requests they can t resolve themselves Conditional forwarder DNS server to which other DNS servers send requests targeted for a specific domain Caching-only server Does not have zones; it fields DNS queries, does recursive lookups to root servers, or sends requests to forwarders and then caches the results MCTS Windows Server 2008 Active Directory 10
DNS Zones Three different types of zones Primary zone Contains a read/write master copy of all resource records for the zone; it is considered authoritative for the zone Secondary zone Contains a read-only copy of all resource records for the zone; it is considered authoritative for the zone Stub zone Contains a read-only copy of only the SOA and NS records for a zone and the necessary A records to resolve NS records; not authoritative MCTS Windows Server 2008 Active Directory 11
Installing DNS DNS installation begins by installing the DNS Server role in Server Manager If the DNS server is intended to manage domain name services for Active Directory, DNS Server role should be installed on a domain controller Windows automatically detects whether or not the server is configured as a domain controller and then integrates DNS zones with Active Directory MCTS Windows Server 2008 Active Directory 12
Creating DNS Zones An Active Directory integrated zone is a primary or stub zone with the DNS database stored in an Active Directory partition Installing DNS on a domain controller that is part of an existing domain will have zone information copied to it automatically during AD replication Some situations may require that a zone be created manually Zones that are not Active Directory integrated are referred to as standard zones MCTS Windows Server 2008 Active Directory 13
Creating DNS Zones (cont.) MCTS Windows Server 2008 Active Directory 14
Active Directory-Integrated Zones Store the zone in Active Directory check box means you want the zone stored in an Active Directory partition Standard zones are stored in a text file called zonename.dns, which is located in the %systemroot%\system32\dns folder Active Directory-integrated zones have the following advantages over a standard zone: Automatic zone replication Multimaster replication and update Secure updates Efficient replication MCTS Windows Server 2008 Active Directory 15
Zone Replication Scope After selecting the zone type and specifying the zone to be stored in Active directory, you are asked to select the zone replication scope with one of these options: To all DNS servers in this forest To all DNS servers in this domain To all domain controllers in this domain (for Windows 2000 compatibility) To all domain controllers specified in the scope of this directory partition MCTS Windows Server 2008 Active Directory 16
Forward and Reverse Lookup Zones Next, you are asked whether a zone should be a forward lookup zone or a reverse lookup zone FLZ Forward lookup zone contains records that translate names to IP addresses, such as A, AAAA, and MX records RLZ Reverse lookup zones contain PTR records that map IP addresses to names and is named after the IP network address (IPv4 or IPv6) of the computers whose records it contains MCTS Windows Server 2008 Active Directory 17
Dynamic Updates Final step allows you to choose whether and how to use dynamic updates, which can be configured in one of three ways Allow only secure dynamic updates Allow both nonsecure and secure dynamic updates Do not allow dynamic updates Dynamic updates enable DNS client computers to register and dynamically update their resource records with a DNS server whenever changes occur MCTS Windows Server 2008 Active Directory 18
Creating Zones from the Command Line Dnscmd.exe can create and configure various DNS settings Basic syntax: dnscmd server /command Examples: Create a new primary Active Directory-integrated zone named zone1 that allows only secure dynamic updates: dnscmd server99 /ZoneAdd zone1 /DsPrimary Add an A record for the host named host1 in zone1 with the IP address 192.168.200.99: dnscmd server99 /RecordAdd zone1 host1 A 192.168.200.99 MCTS Windows Server 2008 Active Directory 19
Configuring DNS Zones Zones can be viewed and changed in DNS Manager DNS Manager provides the following options: Status Type Replication Dynamic updates Aging MCTS Windows Server 2008 Active Directory 20
Configuring DNS Zones (cont.) MCTS Windows Server 2008 Active Directory 21
Aging and Scavenging Resource Records Stale resource records can degrade server performance, provide incorrect information, and generally make DNS less reliable and efficient Enabling scavenging causes the server to check for stale records periodically and deletes those meeting the criteria for a stale record Options in the Zone Aging/Scavenging Properties dialog box Scavenge stale resource records No-refresh interval Refresh interval The zone can be scavenged after MCTS Windows Server 2008 Active Directory 22
Start of Authority Records SOA records are found in every zone and contain information that identifies the server primarily responsible for the zone as well as some operation properties for the zone The SOA record contains the following information: Serial number Primary server Responsible person Refresh interval Retry interval Expires after Minimum (default) TTL MCTS Windows Server 2008 Active Directory 23
Name Server Records NS records specify FQDNs and IP addresses of authoritative servers for a zone NS records are also used to refer DNS queries to a name server that has been delegated authority for a subdomain Glue A records are A records containing a name server s IP address and are used to resolve NS record information MCTS Windows Server 2008 Active Directory 24
Zone Delegation Zone delegation is transferring authority for a subdomain to a new zone, which can be on the same server or another server The server hosting the parent zone maintains only an NS record pointing to the DNS server hosting the delegated zone _msdcs subdomain exists inside every Windows domain zone and holds SRV records for Microsofthosted services, such as global catalog, LDAP, and Kerberos MCTS Windows Server 2008 Active Directory 25
Zone Delegation (cont.) MCTS Windows Server 2008 Active Directory 26
Using Stub Zones Stub zones are a special type of zone that contain only an SOA record, one or more NS records, and the necessary glue A records to resolve NS records Reasons for using stub zones Maintenance of zone delegation information In lieu of conditional forwarders Faster recursive queries Distribution of zone information MCTS Windows Server 2008 Active Directory 27
Zone Transfers A zone transfer copies all or part of a zone from one DNS server to another and occurs as a result of a second server requesting the transfer from another server Zone transfers can be initiated in two ways Refresh interval DNS notify Zone transfers are configured in the Zone Transfers tab of a zone s Properties dialog box, which has the following options: Allow zone transfers To any server Only to servers listed on the Name Servers tab Only to the following servers Notify MCTS Windows Server 2008 Active Directory 28
Incremental Zone Transfers Two types of zone transfer Full zone transfers Incremental zone transfers Both master and slave DNS servers must support incremental zone transfers to use them During the initiation of an incremental zone transfer, the serial number decides whether the slave or the master determines the differences between its current zone data and the zone data on the other server MCTS Windows Server 2008 Active Directory 29
Using WINS with DNS Windows Internet Name Service (WINS) is a legacy name service used to resolve NetBIOS names, sometimes referred to as single-label names Similar to DNS in that it keeps a database of name-toaddress mappings Generally used in environments that require NetBIOS resolution or where applications depend on it The WINS tab has the following options: Use WINS forward lookup Do not replicate this record IP address Time to live (TTL) MCTS Windows Server 2008 Active Directory 30
Using the GlobalNames Zone GlobalNames zone (GNZ) allows administrators to add single-label names to DNS, giving client computers the ability to resolve these names without including a DNS suffix in the query Entries must be made manually Can assist mobile users by dropping the need for remembering a resource s FQDN Enabled via dnscmd.exe Dnscmd server /config /EnableGlobalNamesSupport 1 MCTS Windows Server 2008 Active Directory 31
DNS Forwarders Referring a DNS query to a forwarder can be more efficient under some situations When the DNS server address for the target domain is known When only one DNS server in a network should make external queries When a forest trust is created When the target domain is external to the network and an external DNS server s address is known Conditional forwarding allows queries for particular domains to particular name servers and all other unresolved queries to a different server MCTS Windows Server 2008 Active Directory 32
Configuring Traditional Forwarders To configure a traditional forwarder, right-click the server node in DNS Manager, click Properties, and click the Forwarders tab If more than one server is specified, they are queried in the order in which they re listed Additional servers are only queried if the first server provides no response No response from any forwarders triggers a normal recursive lookup process, starting with a root server MCTS Windows Server 2008 Active Directory 33
Configuring Conditional Forwarders Previously, traditional and conditional forwarders were configured under the Forwarders tab, but Server 2008 has conditional forwarders as a node in DNS Manager With forwarders and/or conditional forwarders configured, the DNS server attempts to resolve DNS queries in this order: 1. From locally stored zone resource records 2. From the DNS cache 3. From conditional forwarders 4. From traditional forwarders 5. Recursively by using root hints MCTS Windows Server 2008 Active Directory 34
Root Hints Root hints consist of a list of name servers preconfigured on Windows DNS servers that point to Internet root servers These servers contain lists of name servers that are responsible for top-level domains Root hints data comes from the Cache.dns file located in the %SystemRoot%\System32\DNS folder Internal DNS servers can be configured as root servers if the network is isolated from the public Internet MCTS Windows Server 2008 Active Directory 35
Round Robin Load sharing can be configured among servers running mirrored services Accomplished by creating multiple A records with the server s name in both records but with each entry configured with a different IP address DNS will then respond to queries by sending all addresses associated with the server s name but will also vary their order This process is called round robin because each IP address is placed first in the list an equal number of times MCTS Windows Server 2008 Active Directory 36
Recursive Queries Recursion is enabled on Windows DNS servers by default, but there are two ways to change this setting First involves configuring forwarders Second is the Disable recursion (also disables forwarders) option in the Advanced tab of the DNS server s Properties dialog box Recursion might be disabled when you have a public DNS server containing resource records for your publicly available servers, but you don t want unauthorized users using your DNS server for recursive client requests MCTS Windows Server 2008 Active Directory 37
Event and Debug Logging When DNS is installed, a new event log is created to record informational, error, and warning events generated by the DNS server Common events include zone serial number changes, zone transfer requests, and DNS server startup and shutdown events Debug logging can be enabled in the server s Properties dialog box Debug logging records selected packets coming from and going to the DNS server in a text file MCTS Windows Server 2008 Active Directory 38
Event and Debug Logging (cont.) MCTS Windows Server 2008 Active Directory 39
DNS Troubleshooting Windows has several tools to administer, monitor, and troubleshoot DNS server operation, including the following tools: DNS Manager Dnscmd.exe Event Viewer Dnslint Nslookup Ipconfig Performance Monitor Protocol analyzer MCTS Windows Server 2008 Active Directory 40
Monitoring DNS Performance DNS performance can degrade over time because of increased database size and increased client activity Dnscmd.exe can display a snapshot of server statistics with the dnscmd.exe /statistics command Performance monitor can continuously monitor and gather statistics Creating a performance baseline is good practice for troubleshooting issues that may arise later on MCTS Windows Server 2008 Active Directory 41
Monitoring DNS Performance (cont.) MCTS Windows Server 2008 Active Directory 42
Chapter Summary DNS is based on a hierarchical naming structure and a distributed database DNS can be described as an inverted tree with the root domain at the top, TLDs branching off the root, and domains and subdomains branching off TLDs The DNS database is composed of zones containing resource records, such as Start of Authority (SOA), Host (A), and Service (SRV) records MCTS Windows Server 2008 Active Directory 43
Chapter Summary (cont.) DNS lookups involve iterative and recursive queries Most lookups start from the DNS resolver with a recursive query to a DNS server; the DNS server satisfies the query or performs a series of iterative queries, starting with a root server DNS servers can perform one or more of the following roles: authoritative server, forwarder, conditional forwarder, and caching-only server Active Directory-integrated zones have the advantages of automatic replication, multimaster replication, and update, secure updates, and efficient replication MCTS Windows Server 2008 Active Directory 44
Chapter Summary (cont.) A zone can be a forward lookup zone or a reverse lookup zone SOA records contain information about a zone, including its serial number and a number of timers used for zone transfers Subdomains can be delegated to a zone on another server to improve performance and control replication scope Advanced DNS settings include configuring forwarders, root hints, round robin, recursive queries, and logging MCTS Windows Server 2008 Active Directory 45
Chapter Summary (cont.) Tools for monitoring and troubleshooting DNS include Dnscmd, Dnslint, Nslookup, Ipconfig, and Performance Monitor You need to understand the DNS query process to troubleshoot DNS problems efficiently MCTS Windows Server 2008 Active Directory 46