What Is a DHCP Client ID?

The Dynamic Host Configuration Protocol (DHCP) plays a major role in how your computer networks with other computers. DHCP allocates IP addresses to computers on a network before the computer boots up. Understanding the basics of DHCP helps you understand and troubleshoot computer networking issues.

Internet Protocol (IP) addresses are numerical and attached to computers. Computers must have an IP address to contact other computers across the internet. As the number of computers in use has dramatically increased over the years, so has the demand for IP addresses. Internet service providers (ISPs) and network administrators use a method called Dynamic IP addressing to ensure that enough IPs remain available for existing and future computers.

Dynamic IP addressing is a response to the number of computers on the network being greater than the number of IP addresses in the pool. A computer needs an IP address while it is connected to the network, but it does not need to keep the same IP address permanently. As a result, if your ISP practices dynamic IP addressing, your computer's IP address refreshes frequently. This isn't a problem unless you use services that require a static IP address, such as Windows Remote Access.

The network adapter on your computer is responsible for converting data from your computer into the format required to travel over the internet. Your computer's network adapter adheres to the DHCP procedures. When you turn your computer on, your network adapter contacts the DHCP server on your network to get the IP address for your computer. The network adapter also performs the task of listening for silence on the network cable and applying a signal when silence is detected.

The Media Access Control (MAC) address is the DHCP client ID that is sent by the network adapter to the DHCP server. The MAC address is the physical address of your computer and is a unique serial number that does not change. Network gateways that stand at the access point between the local network and the internet maintain a lookup table that cross-references the MAC addresses and IP addresses on the network. The MAC address is sent as the DHCP client ID by default. Network administrators can override this, however, and enter a custom series of DHCP client IDs on each computer.

There are times where you may need to find your DHCP client IP. How you find the DHCP client ID depends on whether your computer has the Mac or Windows operating system installed. To find the DHCP ID on a Windows computer, click the Windows "Start" button on the bottom left side of the screen and then type "cmd" into the search bar. Click the "Command Prompt" program to launch it. Type "ipconfig /all" to display your computer's network settings. The MAC address is displayed next to the Physical Address field. You can also see the IP address in this same box.

Find the DHCP client ID on a Mac computer by clicking the "Apple" icon in the top left corner of the screen and then select the "System Preferences" option. Click the "Network" icon in System Preferences and then click the "Advanced" button within Network. Click the "Hardware" tab to show information about your network hardware. The Mac's MAC address is displayed here as well.