What are Root Hints?


Windows DNS Server Root Hints

Что такое Windows DNS Server Root Hints

Microsoft Windows DNS Server Root Hints — это фрагмент конфигурации DNS-сервера Windows, который указывает маршруты DNS-запросов в случае, если запрашиваемый домен не может быть найден в локальных кешах DNS-сервера.

Root hints содержит информацию о корневых серверах, где хранятся информация о доменах первого уровня в глобальной сети Интернет. Каждый DNS-сервер Windows должен знать, куда отправлять DNS-запросы, если нужно найти корневой домен в Интернете.

Root hints представляют собой набор данных о корневых доменах и корневых серверах. Другими словами, это набор файлов, находящихся в системной папке DNS-сервера Windows и содержащих информацию о корневых серверах, на которые следует перенаправлять DNS-запросы, которые невозможно обработать на локальном сервере.

Root hints are DNS data stored in a DNS server. The root hints provide a list of preliminary resource records that can be used by the DNS service to locate other DNS servers that are authoritative for the root of the DNS domain namespace tree.

Root hints are used to prepare servers authoritative for non-root zones so that they can learn and discover authoritative servers that manage domains located at a higher level or in other subtrees of the DNS domain namespace. These hints are essential for servers authoritative at lower levels of the namespace when locating and finding servers under these conditions.

For example, If a DNS server (ServerA.corp.com) is answering a query for a domain, such as the anITKB.com domain, ServerA needs some assistance to locate an authoritative server (ServerB.anITKB.com) for this domain. In order for ServerA to find ServerB, or any other servers that are authoritative for the anITKB.com domain, it needs to be able to query the root servers for the DNS namespace.

By default, the DNS Server service implements root hints using a file, named Cache.dns, stored in the %systemroot%System32Dns folder on the server computer. This file normally contains the NS and A resource records for the Internet root servers.

If, however, you are using the DNS Server service on a private network, you can edit or replace this file with similar records that point to your own internal root DNS servers.

Note:If you are operating internal root servers, do not use root hints. Instead, delete the Cache.dns file entirely for any of your root servers. Your internal root server(s) need(s) to host a forward lookup zone called “.”

Domain Name System is the internet’s phonebook.

DNS is used to convert/map the domain name to an IP address.

To access a website, a client needs to know the site’s IP address, but it is tough to remember the IP addresses of each website.

A domain name is easy to remember instead of remembering the IP address of each website.

The website/requested URL is forwarded to the DNS server, and the DNS server returns the IP address for the requested website. The client is then able to access the requested site.

What is DNS root hints:

Root hints provided a list of IP addresses of DNS servers considered authoritative at the root level of the DNS hierarchy.

If the DNS server does not know the address of the requested website, it will forward the request to another DNS server.

The DNS server must know the IP address of another DNS server to forward the request.

DNS Server will contact Root Hints only when no Forwarders are available or cannot resolve the query.

Root hints are preconfigured on DNS servers. The root hints are stored in a file named CACHE.DNS that is located in at below folder.

How to check ROOT Hints:

Open DNS Server

Right-click on the DNS server name and click on Properties.

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Step3: Click on the Root Hints tab to view Root Hints.

You can add, remove and edit Root Hint from here.

What is DNS Recursion:

means the DNS server will not query to any other DNS server apart from its cache or within its local DNS server.

When we configure a DNS server to allow recursion, the server queries other DNS servers to request clients resolve domain names that are not authoritative.

It also increases the system’s vulnerability to DNS attacks if the DNS recursion is not disabled.

Disable recursion DNS:

Open DNS Server and Right click on DNS server.

Click on Properties and

Go to Advanced Tab

Click on the «Disable recursion» check box under the Server section to disable recursion.

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There are two ways to direct DNS queries out of your organization: root hints and DNS forwarders. Root hints are simply pointers to DNS servers that are higher in the DNS hierarchy, sometimes to the most authoritative DNS servers on the Internet. Root hints are used to configure servers that are authoritative for non-root zones such that they can discover authoritative servers that manage domains located at a higher level of the namespace or in other subtrees. The best use of root hints is on internal DNS servers at lower levels of the namespace. Root hints should not be used for querying DNS servers outside your organization; DNS forwarders are better equipped for performing this function.

DNS forwarders are DNS servers on your network that are used to forward DNS queries for a separate DNS namespace from internal DNS clients to DNS servers that can resolve the query. In a manner of speaking, the key difference between root hints and forwarders is that forwarders create a chain of DNS servers that ascend the DNS hierarchy, while root hints shoot right for the top. You designate a DNS server on a network as a forwarder by configuring the other DNS servers in your network to direct those queries that cannot be resolved to that particular server. A DNS forwarder is the sole means for enabling name resolution for host names in external namespaces, notably the Internet. It can also improve the efficiency of name resolution by offloading the processing of queries to other DNS servers, rather than performing some very resource intensive, constant replication of external namespaces. A new DNS feature that was introduced with Windows Server 2003 is Conditional Forwarding, which uses forwarders that can be configured to forward queries according to specific domain names to make name resolution more efficient.

When a DNS client sends a query to a DNS server, the DNS server looks at its own database to see if the query can be resolved using its own zone data. The server will also examine its cache of resolved queries and send the data back to the client that sent the query. If the DNS server is configured to forward for the domain name designated in the query, the query is forwarded to the IP address of the DNS forwarder that is associated with that domain name. If the DNS server has no forwarder listed for the name designated in the query, it attempts to resolve the query using standard recursion.You can use conditional forwarders to enhance and improve upon both internal and external name resolution.

Remember that with a stub zone, certain records exist on the DNS server hosting the stub zone, whereas a conditional forwarder is used to forward DNS resolutions to specific DNS servers based on domain name.

In planning your DNS namespace, you will encounter situations in which you might need to use any of the types of forwarders that we discussed. The way you configure your forwarders within your environment will affect how well queries are answered. If your forwarding scheme is poorly designed, it will affect your ability to properly direct and resolve these queries. For this reason, you need to consider some issues prior to implementing forwarders into your environment:

■ Keep it simple Implement only as many forwarders as necessary for optimum resolution performance. If possible, don’t overload internal DNS servers with dozens of DNS forwarders. Keep in mind that every time a DNS server attempts to process a query, it first attempts to resolve it locally, and then forwards it sequentially through its list of known DNS forwarders.This creates additional overhead by using system resources to complete the query request.

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■ Balance is key One common mistake in using DNS forwarders is pointing multiple internal DNS servers to a single, external DNS forwarder. This practice simply creates a bottleneck within your environment. To keep a DNS forwarder from becoming a bottleneck—and a single point of failure—consider creating more than one DNS forwarder and load-balance your forwarding traffic.

■ No «chains of love» Unless it is completely unavoidable, do not chain your DNS servers together in a forwarding configuration. In other words, if you are configuring your internal DNS servers to forward requests for www.learn-aboutdns.com to server X, do not configure server X to forward requests for

www.learnaboutdns.com to server Y, and so on. Doing so will just create additional overhead and increase the amount of time it takes to resolve a query.

■ Know your forwarders In our discussion of conditional forwarders, we mentioned how they could be used for Internet resolution outside your environment. If you plan to use conditional forwarders in this manner, make sure that you know where these forwarders are and who is managing them. For example, make sure that company XYZ is not using a third-party DNS hosting company (such as www.mydns.com) to host their DNS names.You must also be sure you trust your forwarders to be available and that their IP addresses do not change. These servers can potentially be anywhere in the world and run by any number of people.

■ Remember the big picture Keep your entire infrastructure in mind when you are configuring a forwarding scenario. In our Name Resolution University example, it wouldn’t make sense to forward requests from the Vancouver office to the Halifax office, considering that the query would have to cross North America. Since there are other network «hops» between Vancouver and Halifax, this would be inefficient. Examine your network bandwidth prior to implementing DNS forwarders, and even when sufficient bandwidth exists, try to keep your DNS forwarders in the same physical location as your internal DNS servers.

Continue reading here: Active Directory Integrated versus Primary Zones

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Конфигурация Windows DNS Server Root Hints

Некоторые компоненты Root hints, включая файлы zone.root и cache.dns, являются стандартными частями DNS-конфигурации Windows и обновляются в процессе обновления системы. В базовой конфигурации Root hints имеет записи о двух корневых серверах: A и B. Если Root hints установлен правильно, DNS-сервер Windows может автоматически получать доступ к этому файлу и использовать его, чтобы искать домены.

Некоторые управляющие записи, которые могут быть добавлены к Root hints, включают следующие:

How Do Root Hints Work?

The root hints file contains a list of thirteen root nameservers, identified by letters “a” through “m”. Each root nameserver typically has multiple IP addresses associated with it, which improves resilience in the case of network failure or downtime.

A Windows DNS server uses root hints to perform Internet or external DNS lookups when it doesn’t have the requested information in its local DNS zone files. In this case, the server sends a recursive DNS lookup request to one of the root nameservers, together with the requested domain name.

The root nameserver responds with a referral to the TLD nameservers responsible for that particular domain. The DNS server sends another recursive query to one of these servers with the domain name, and the process continues until a match is found.

If the initial root server doesn’t respond, then the automatic failover mechanisms within the DNS server will try the next available root server until a successful match is found or all thirteen servers have been exhausted.

How to configure Root Hints?

Why Are Root Hints Important?

Root hints are an essential component of the DNS infrastructure. They provide a consistent and reliable way for servers to locate relevant nameservers when they don’t have the required information locally. Without root hints, DNS servers would have no way of locating TLD nameservers or unknown domains outside their local network.

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Moreover, root hints establish the hierarchy and authority of the DNS, which enables the Internet to function smoothly and efficiently. They provide a way for DNS servers to validate the authenticity of requests and prevent potential security breaches or DNS hijacks by malicious third parties.

Зачем нужен Windows DNS Server Root Hints

Root hints необходим для перенаправления DNS-запросов на другие DNS-сервера, когда запрашиваемый домен не может быть найден на текущем DNS-сервере Windows. Без этой функции многие DNS-запросы будут отклонены а без этого сервер не сможет осуществлять связь между узлами в Интернете.

What Are Root Hints?

Root hints are a small database residing on a DNS server. They contain a list of well-known top-level domain (TLD) nameservers, including their corresponding IP addresses.

Root hints are important because they allow servers to find records that they don’t already have, and they establish the hierarchy and authority of the DNS.

Why are Root Hints important for DNS Server management?

Root Hints are essential for DNS Server management as they allow the Windows DNS Server to resolve domain names quickly and accurately. Without Root Hints, the DNS Server would need to send every query to the root name server to resolve the domain name, delaying the process and introducing points of failure in the infrastructure.

Как установить Windows DNS Server Root Hints

Windows DNS Server Root Hints предустановлен на каждом сервере DNS Windows, и обновлять его можно с помощью мастера настройки DNS. Если необходимо изменить Root Hints на DNS-сервере Windows, следует перейти в раздел «DNS-серверы» в панели управления устройством и открыть свойства DNS-сервера. Затем нажмите на кнопку «Root Hints» и добавьте или измените соответствующие записи.

Windows Domain Name System (DNS) servers often rely on root hints to perform lookups for domain names not stored in their local zone files. The root hints file contains a list of nameservers running at the root level of the DNS hierarchy, and it provides the address records for those nameservers.

Root Hints are a set of preconfigured DNS server addresses that act as reference points for the Windows DNS Server to resolve domain names that are not already stored in its local cache. The Root Hints contain the IP addresses for the 13 root name servers that manage the top-level domain names (.com, .org, .net, etc.) and the generic top-level domain names (gTLDs) like .com, .info, .biz, etc.

The Root Hints redirect the Windows DNS Server to the correct root name server for a specific domain name, allowing the DNS Server to resolve domain names and route network traffic accurately.

Best Practices for Root Hints

Every time the Windows DNS Server receives a query for a domain name that is not stored in its local cache, it contacts one of the Root Hints to resolve the domain name. The Root Hint returns the IP address of the root name server that manages the domain name. The Windows DNS Server then forwards the query to the root name server which returns the IP address for the authoritative name server (ANS) for the domain name.

The Windows DNS Server then contacts the ANS to resolve the domain name and returns the IP address to the client that initiated the query.


Windows DNS Server Root Hints является необходимой функцией для всех DNS-серверов Windows и обеспечивает связь между узлами в Интернете. Root hints позволяет Windows DNS-серверу выполнять DNS-запросы и содержит информацию обо всех корневых серверах доменов, находящихся в глобальной сети Интернет. Как мы выяснили, Root hints устанавливается на каждом сервере DNS Windows и обновляется с помощью мастера настройки DNS.


Root hints are an essential part of the DNS infrastructure, providing a way for servers to locate and validate relevant nameservers. By automatically downloading the latest list of root nameservers, a Windows DNS server can ensure that it has the most accurate and up-to-date information available.

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