DNS Best Practices: Architectures that Work

Every Connection Starts with DNS

DNS is a core network service. You’d be hard pressed to think of a service, public or private, that doesn’t rely on DNS at some point. Without reliable DNS your business applications including email, web services, ERP, CRM and VoIP cannot function. A core services outage can also have consequences you might not have considered: for example, if entry and exit to your office is controlled by IP and relies on DNS, employees might not be able to get into the building, or worse, might find themselves locked in the cafeteria.

Whether your network architecture is simple or extremely complex, a solid network design is critical to maintain a reliable, secure and manageable DNS environment. DNS security, performance and availability are fundamental design objectives. Here are a few tips and general guidelines to help you build a core services architecture that works.

Best Practices for Public DNS:

• Hide Your Valuables – Configure the external primary DNS server as a Hidden Primary. This configuration protects the primary server, provides maximum performance, and increases tolerance to failure. As well, where possible, deploy primary servers in high availability clusters.
• Spread the Load – Deploy secondary servers in geographically-dispersed data centers to avoid a single point of failure scenario. Placing secondary servers within the corporate demilitarized zone (DMZ) minimizes the types of data traffic to which they are exposed, affording greater security.
• Restrict Access – Secure zone transfers using access control lists (ACLs) and transaction signatures (TSIGs). These security measures deter potential attackers.
• Limit Your Exposure – Disable recursion on external servers to eliminate the risk of cache poisoning and other DNS attacks.
• Go to Jail, Go Directly to Jail – Run DNS in a chroot jail to sandbox potential attacks and minimize damage.
• Keep it to Yourself – Hide information that indicates the version of DNS server software deployed. This information benefits attackers who can exploit known vulnerabilities.

Best Practices for Private DNS:

• Keep It Inside – Locate internal DNS servers on the internal network, behind your corporate firewall.
• Secure Access – Use virtual private networks (VPNs) to connect remote users to internal resources.
• Lighten the Load – To enhance performance and reliability, consider using a Hidden Primary for the internal primary DNS server.
• Think Locally – Where possible, deploy secondary servers at local sites to preserve network bandwidth. An analysis of bandwidth requirements – the frequency DNS queries on the local WAN link – can help determine whether small sites warrant secondary servers.
• Conserve Bandwidth – As alternatives to secondary servers, consider stealth secondary servers or caching-only servers for small sites. These require less network bandwidth.
• Take Root – The size and complexity of the internal DNS affects your design decisions. Consider deploying internal root servers for large, distributed networks or those with complex namespaces. Internal root servers can enhance scalability, efficiency and control.