Home > Articles > Certification > Microsoft Certification

This chapter is from the book

Planning DNS Forwarding Requirements

Before a discussion of forwarding and slave DNS servers can be undertaken, some general knowledge of how DNS clients query a DNS server to resolve IP addresses is of some use.

In a TCP/IP network, a DNS resolver is any system that has been configured with one or more DNS server IP addresses and that performs queries against these DNS servers. The DNS resolver is part of the DNS Client service, which is automatically installed when Windows is installed. The resolver can request one of two types of queries from a DNS server: recursive or iterative.

A recursive query is a DNS query that is sent to a DNS server from a DNS resolver asking the DNS server to provide a complete answer to the query, or an error stating that it cannot provide the information. If the DNS server is also configured as a forwarder, the query can be forwarded directly to another DNS server. If the query is for a name outside of the local DNS server's zone of authority, it performs an iterative query against a root DNS server, which then responds with the IP address of the DNS server whose zone of authority includes the desired IP top-level domain. Additional iterative queries are then performed until the name is resolved into its IP address or an error is produced.

An iterative query is a DNS query that is sent by a DNS server to another DNS server in an effort to perform name resolution. Consider the example of a workstation (DNS resolver) in the bigcorp.com domain that wants to communicate with a Web server located in the smallcorp.com domain. Figure 3.3 illustrates the process by which the IP address for http://www.smallcorp.com will be resolved to its IP address. Recall that www is a typical alias for a Web server or bank of clustered Web servers.

Figure 3.3Figure 3.3 The initial recursive query results in several iterative queries in an effort to resolve the name to an IP address.

  1. The DNS resolver (the local workstation) sends a recursive query to its local DNS server requesting the IP address of http://www.smallcorp.com.

  2. The local DNS server, which is also configured as a forwarder, does not have information about http://www.smallcorp.net in its zone of authority and thus issues an iterative query to a root DNS server for the IP address of http://www.smallcorp.com.

  3. The root DNS server does not have the requested information about the IP address of http://www.smallcorp.com, but it does know the IP address of a nameserver for the smallcorp.com zone. It provides this information back to the requesting DNS server.

  4. The local DNS server next issues an iterative query to the DNS server for the smallcorp.net zone asking it for the IP address of http://www.smallcorp.com.

  5. The smallcorp.net DNS server is authoritative for that zone, so it provides the requested IP address back to the local DNS server for http://www.smallcorp.com.

  6. The local DNS server next passes the IP address of http://www.smallcorp.com back to the requesting workstation.

  7. The client can now make a connection to http://www.smallcorp.com.

So, with the discussion of how DNS queries are performed and resolved under your belt, you can begin to plan for configuration and usage of DNS forwarders on the network.

A DNS forwarder is a DNS server that accepts forwarded recursive lookups from another DNS server and then resolves the request for that DNS server. This can be useful if you do not have local copies of your internal DNS zone and want to have your local DNS server forward DNS queries to a central DNS server that is authoritative for your internal DNS zone. Caching-only servers make good DNS forwarders. If the DNS forwarder does not receive a valid resolution from the server that it forwards the request to, it attempts to resolve the client request itself.

A DNS slave server is a DNS forwarder server that will not try to resolve a resolution request if it doesn't receive a valid response to its forwarded DNS request. You will typically see this type of DNS server implemented in conjunction with a secure Internet connection.

A new feature in Windows Server 2003, conditional forwarding, enables administrators to direct DNS requests to other DNS servers based on domain. Previous versions of Microsoft DNS supported only one forwarder, so if forwarding were enabled, all requests would be sent to a single server. This is used frequently when you want requests made to the internal network to be forwarded to a master DNS server that stores internal DNS zones, but have resolution requests that are made to Internet domains be sent to the Internet using the standard resolution process.

TIP

Because enabling conditional forwarding is a new capability with Windows Server 2003's DNS service, you need to be familiar with how this works and when you might need to use it.

Figure 3.4 shows the Forwarders tab of the DNS server Properties dialog box.

Let's say that you have a single internal domain called lab1.area51partners.com. You need to forward any queries to that domain directly to the primary DNS server for the lab1.area51partners.com domain. The Windows Server 2003 DNS service enables you to configure forwarding for a single domain, a group of domains, or all domains. Earlier versions of the Windows DNS service supported only forwarding of all domains—it was an all-or-nothing proposition. The functionality of being able to split forwarding among multiple servers while still resolving some domains locally is known as conditional forwarding. Figure 3.5 shows the IP address that has been configured for conditional forwarding to the internal domain.

Figure 3.4Figure 3.4 The Forwarders tab is used configure where this server will send DNS requests if another DNS server will be supplying some or all of the DNS resolution for that server.

Figure 3.5Figure 3.5 Conditional forwarding enables you to configure specific DNS servers by domain.

NOTE

If you disable recursion in the DNS server properties, you will not be able to use a forwarder. Forwarding DNS requests requires that the DNS server be capable of making recursive queries.

A common implementation of DNS forwarders in a Windows Server 2003 network has one specific DNS server being allowed to make queries to DNS servers outside of the firewall. This allows the firewall to be configured to allow DNS traffic only from this specific DNS server to leave the protected network, and allows only valid replies back to the DNS server to enter the protected network. Through this approach, all other DNS traffic—both inbound and outbound—can be dropped at the firewall, adding to the overall security of the network and the DNS service. Figure 3.6 illustrates this concept.

Figure 3.6Figure 3.6 DNS forwarders can be implemented to control DNS traffic into and out of the protected network.

Forwarders can be used to ensure that DNS queries have the best possible chance of being answered with the requested information. As you have seen, they also can be implemented to increase security of the DNS service on your network. With security in mind, we examine other ways you can configure additional security on your DNS servers.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020