Dynamic DNS Overview

The domain name system (DNS) has become familiar to many people, but not everyone realizes that associated IP addresses are in somewhat limited supply. For the time being, internet service providers (ISPs) are circumventing this shortage by giving their customers dynamic IP addresses. These IP addresses change frequently, and dynamic DNS (DDNS) software automatically logs these changes to ensure static domain names remain associated with the appropriate new IP addresses.

Before dynamic DNS, admins were required to manually configure DNS server records, so the increasing use of dynamic DNS over the past decade has saved admins a great deal of time. As such, it’s absolutely essential for managed services providers (MSPs) to be aware of what dynamic DNS is, and why they may need to invest in DDNS solutions for their customers.

What is DNS vs. DDNS?

The Domain Name System is a distributed database that supports the foundational method of mapping IP addresses to device names. Dynamic DNS is a method of updating and changing the DNS automatically in real time.

In a sense, DNS is a “phonebook,” as it provides the domain names, like www.solarwindsmsp.com, that people use to access web pages online. Behind these domain names are IP addresses that browsers use to actually establish connections. You could theoretically use just a numeric IP address, typically in a form similar to 12.34.56.78, but that isn’t as user-friendly as domain names, and would lack SSL certificate security.

DNS information is housed at the central registry, and ISPs have to interact with this registry to get current DNS information. One central root server handles the overall database, but there are also millions of distributed DNS servers that work to handle domain name queries. Many ISPs run local servers on which they keep a copy of IP addresses in order to minimize the work performed by the root servers. At this point, there are a limited number of IPv4 addresses, which has led both to the development of IPv6 and the widespread use of dynamic DNS.

How does dynamic DNS work?

Essentially, a dynamic DNS service creates a permanent name for a changing IP address. For smaller businesses or residential users, there’s no need for a costly static IP address—these are rare these days, and typically, only larger businesses opt to invest in them. Further, many businesses in rural locations can’t have static IP addresses. Instead, it’s more likely that customers will use a dynamic DNS configuration to maintain connectivity.

In this context, “dynamic” means the ISP-provided IP address frequently changes without prior notice. This is necessary due to the limited number of available IP addresses, but can occasionally be inconvenient. One common concern is that it might become tricky to use a set IP address for other purposes—like accessing a remote webcam or security camera. But in fact, dynamic DNS is a way of assigning a custom domain name that automatically updates even as the IP address changes. This system has been around long enough that there are workarounds for these kinds of issues.

In short, reliability is actually one of the value-adds of dynamic DNS—you can be confident your system will connect the right domain name to the changing IP address. With DDNS, your domain name doesn’t change, but the associated IP address will change behind the scenes. With a dynamic DNS program on your device, each time you connect, you will receive a dynamic public IP address from your ISP. When this IP address changes, the software updates your account with the new IP address to maintain the connection to the right host server. Most modern modems and routers include firmware compatible with various DDNS providers.

At a technical level, standards-based DNS updates are prescribed by RFC 2136, a network protocol used by DNS servers, typically within the dynamic host configuration protocol (DHCP) system. RFC 2136 has security features and is supported by software within most operating systems and directory services like Active Directory (AD). Note that the security features of this protocol are not necessarily enough to overcome certain additional security concerns associated with DDNS.

What is DNS dynamic update?

Dynamic DNS updating involves changing the IP address associated with a DNS record. The changes happen automatically, in real time, and are not noticed by the user.

Previously, this kind of change may have been done manually, but by using an update client, updates can now be lightweight, fast, and behind the scenes. The host computers are able to receive an address from a DHCP server or through automatic configuration, then notify the DNS server. DNS updates can be configured through the server, allowing DDNS client computers to update their resource records whenever the changes happen. It’s also possible to disable this feature if it’s not needed or if it’s causing security issues.

What is dynamic DNS used for?

Dynamic DNS is used for IP address management, often for residential or small business customers, or for any business for whom a static IP address is not an option. It is also useful for Active Directory functions, remote and changing device location, and remote access.

For instance, when workstations join a domain, Active Directory uses DDNS to create DNS entries so hosts can track these devices. AD can track when IP addresses and host names join and leave the network, and update DNS records as needed. Clients enrolled in Active Directory can dynamically update their DNS records when the IP address changes, while AD ensures that inactive records are removed.

Additionally, dynamic DNS is useful for organizations with devices that may move to various locations and even connect to other networks. With DDNS, it’s possible to maintain device IP address updates despite these changes. Similarly, dynamic DNS allows for remote control functionality. If you need to access a device that has a changing IP address like a home device or small business security camera, you can utilize the fixed domain name. This may require software that takes dynamic DNS updates into account.

Dynamic DNS and DHCP

Typically, DDNS means the client device gets its IP settings from a dynamic host configuration protocol (DHCP) server. DHCP is a network protocol that allows the server to automatically assign an IP address—whether static or dynamic—to a computer. When a user turns on a computer with a DHCP client, the broadcast request goes to the DHCP server, which then assigns the appropriate address. For homes or small businesses, the router acts as the DHCP server.

DHCP makes it easy to automatically add devices, so it’s useful for larger networks, especially since the alternative to using DHCP is to manually assign an address to every device. While the DHCP server can distribute static addresses, with dynamic IP address assignment, the chances are lower that two devices will use the same IP address.

Once the DHCP server has assigned an IP address, it can communicate this to a DNS server, which then updates that information. Or, the client itself can transmit the information to the DNS server. It’s important to note that dynamic IP addresses are not appropriate for devices that need ongoing access like printers or file servers. Offices should not use DHCP for these devices, as that would require workstations to constantly reconfigure their connections.

As an MSP, you may be called on to configure dynamic DNS for your customers or set up a DHCP server.