DNS Server Best Practices for Security and Configuration

DNS Server Best Practices for Security and Configuration. In this post, we will have a look at some DNS server best practices for security and configuration. We will talk about the 10 most critical steps to make sure you get the best out of your DNS installation.

Let’s start with our article DNS Server Best Practices for Security and Configuration.

What is a DNS server?

A domain name server or DNS is often called the phone book of the internet. Just like the outdated telephone directory, it makes us – the user or “dialler” – find out what the name corresponds with a given number. Similarly, a unique address number identifies a DNS server’s domain. This address is the IP address.

When we type in a URL, our browser contacts the DNS to “translate” it into the domain’s corresponding IP address. After that, we navigate the internet using this IP address, which is more machine friendly. Our browser uses this “digital address” to find, the domain’s host. Subsequently, we easily retrieve resources that are shared on it.

This, of course, is the abridged version of how a DNS server works. If you want to find out more, have a look at our post entitled “What is DNS Hierarchy Architecture with Examples.” In it, you have the back-and-forth resolution process that takes place behind the local DNS server.

DNS server - the back-and-forth process
The DNS resolution process is quite complex and has multiple iterations

How will the best practices help you?

The DNS server best practices for security and configuration helps optimize and secure your “digital telephone book” by focusing on:

    • Implementing a backup plan to ensure continuity when a DNS server is down.
    • Securing the DNS server by removing vulnerabilities before they are exploited.
    • Preventing access to malicious websites that infects DNS and the network as a whole.
    • Cutting issue resolution times by making sure you have audit trails to fall back on while troubleshooting.
    • Implementing configurations that ensures communication is fast and efficient without compromising security.

We should proceed to DNS Server Best Practices for Security and Configuration.

10 DNS server Best Practices for Security and Configuration

Ok; let’s move on to the 10 most important steps you need to take to optimize and secure your DNS server:

1. Enable logging and auditing

The best way to monitor DNS activity is with the help of DNS logging. Administrators often use these captured logs to know about any malicious activities. Additionally, it also makes it easy for them to troubleshoot issues when there are problems with processes like queries or updates.

Truly, the DNS logs help with enhancing security. For example, it makes it easier to spot changes in the data cache that have been made by malicious users. They do this to divert traffic to malicious sites that compromise their devices and the data on them. This type of attack is what we call a “cache poisoning” attack.

DNS cache poisoning
DNS cache poisoning - leads users to unwanted websites

One reason administrators decide to disable DNS logging is to improve performance. But, this puts users and devices at risk and  results, at times,  in the whole network going down.

2. Redundancy is vital

Next thing is that businesses should implement at least two servers – a primary and a secondary DNS server. In turn, they ensure their business processes run uninterrupted. The reason here is that a DNS is a critical component of network applications that must be available around the clock.

So, having one DNS server down would mean that vital services like email, file sharing, and AD services will follow. All in all, that depend on the server going down. Therefore, to keep these services running, they need to have a backup DNS server to turn to when the critical one is down.

3. Hide DNS server information

Next point is that, only administrators and privileged users should have access to DNS servers or the data they store. In fact, for the most part, the only information that users should have access to is the server’s IP address.

A primary DNS server should not be visible to users who are outside the network. The server’s records not to be available to external visitors or any publicly accessible name server database. Only, the secondary DNS server is the one addressing requests from end users and the public. If your domain name needs to be visible to external users, for example.

4. Sandbox environment

Any changes and configurations made on a DNS server should be done after it has been removed from a production environment.

A single configuration error isolates users and the network and brings everything to a halt. Therefore, before implementing changes or reconfiguring a DNS server, the actions should be tested in a sandbox or test environment. This way, the production environment remains protected from any mishaps that occur in  the test environment.

5. Regular updates

Hackers are always on on the lookout for vulnerabilities they can exploit in the DNS server software. Firstly, it is one of the primary targets of choice because they can use the DNS server for data exfiltration and command and control attacks.

The best way of patching up the vulnerabilities and preventing such attacks is by making sure the DNS server software always has the latest version and has been updated with the latest patches. And the best way of doing this is by installing a centrally managed solution like an ITSM tool.

6. Locking the DNS cache

Next point is that DNS cache stores all users’ query information and uses it as a reference for future use.  As a result, this results in DNS working faster and having better response times. Especially when the same websites are queried over and over again. The best way to ensure no changes are made to the stored DNS data is by locking the cache.

This is because cybercriminals know how to exploit this storage feature. A TTL (time to live) defines how long a DNS server keeps the lookup information. Therefore, malicious users modify or overwrite the data to show that a TTL has expired, for example. Hence they get in for cache poisoning attacks. Therefore, as a rule of thumb, administrators should completely lock the cache to prevent this alteration and let the TTL run out on its own. Alternatively, until they decide it needs to be purged or refreshed.

Basically, they can set the cache locking scale to 70% (the scale goes up to 100% for complete locking) where changes are made but overwriting the data is not possible for 70% of the data.

7. DNS filtering

Next is DNS filtering involves denying access to certain domains by blocking the name resolution to the sites’ IP addresses.

Apart from enforcing business policies by denying access to sites that are deemed unproductive or unnecessary for the users, DNS filtering also stops them from visiting websites that are deemed to contain malicious content. Therefore, denying access to such sites stops users from getting infected. Also, it prevents networks from being attacked and stops the DNS server itself from being exploited.

On the other hand, a DNS server, a part of a modern software security and firewall solution, is updated regularly with lists of bad domains. Hence, administrators use ready made software solutions to automate DNS filtering as an efficient way of protecting all assets.

8. Configure Access Control Lists

Besides, DNS Access Control Lists (ACLs) [PDF] should be used to control who is allowed to access DNS servers. As a principle, only administrators are able to access a primary DNS server. And only users with permission granted by the ACL can access the servers.

Configure ACL on router
Use your router to define your ACL and stop unauthorized access

In nutshell, using ACLs is critical in securing a DNS server. Primarily it protects from spoofing attacks and unauthorized access attempts. But, apart from users, the ACLs is used to define the servers that are allowed to make zone transfers. This way, any unauthorized user trying to make zone transfer requests is blocked from doing so. Because that is one way that malicious users scope out a business’ network setup.

Certainly, blocking all zone transfer requests over DNS servers by unauthorized users prevents these malicious users from obtaining zone information.

9. Ensure data integrity with DNSSEC

Implementing Domain Name System Security Extensions (DNSSEC) ensures clients receive valid responses to their queries.

As noted, the DNSSEC is a DNS feature that authenticates responses to domain name lookups. Although it does not provide privacy protection for the lookups, it does prevent attackers from manipulating or poisoning the responses sent back to the DNS requests.

So, DNSSEC also digitally signs DNS data to ensure data integrity. When an end-user sends a query, a DNS server embeds a digital signature in the response so clients know they have received valid and verified information for the request they sent.

10. Use the closest DNS server

Consequently, remote sites spread across various locations, are quite common in the modern business network. In these situations, the response time of client machines querying a remote server from a different site with a DNS request takes longer. Mainly because queries need to travel across slower WAN links.

Therefore, when it comes to multi site environments, it is best to point client machines to a local DNS server within the site to reduce the query response times.

Thank you for reading DNS Server Best Practices for Security and Configuration. Le’ts conclude. 

DNS server Best Practices for Security and Configuration Conclusion

Summing up, your DNS server is critical in making sure your network – and all the users that are on it – can communicate in a fast and secure manner. Additionally, it becomes a weak spot that hackers can exploit to compromise your digital assets, if it is not.

Therefore, implementing the 10 DNS server best practices for security and configuration we have just seen, ensures quicker data transfers, whilst diminishing any chances of a breach or data loss. Contact us today to find out more about how we can help with setting up your efficient and secure DNS server.

Take a look at more DNS Server content here

Avatar for Liku Zelleke
Liku Zelleke

Liku Zelleke is a technology blogger who has over two decades experience in the IT industry. He hasn’t looked back since the day, years ago, when he discovered he could combine that experience with his other passion: writing. Today, he writes on topics related to network configuration, optimization, and security for Cloud Infrastructure Services.

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