If you work on a network at home or at your office, you probably already know that multiple devices can be connected at one time to your network. However, have you ever stopped to think of how these devices are identified? They are identified by the DHCP Client ID.
First, what is DHCP?
DHCP stands for Dynamic Host Configuration Protocol. When it is enabled on your network, devices that connect are automatically assigned an IP address without you having to configure each one by hand. This is ideal in office settings where employees connect through their laptops, computers, and smartphones.
In order for DHCP to work, it has to be enabled on a computer, which can be easily done through the Network Setting Properties. Once enabled, IP addresses will be automatically assigned without the need for you to do so manually.
What are DHCP client IDs?
A DHCP client ID is simply how a device identifies itself when it asks the server for an address. By default this is the device’s MAC address - the unique hardware address assigned to its network adapter - but the DHCP protocol also defines a dedicated Client Identifier field (DHCP option 61) that a device can send instead. The server uses this ID to recognize a returning device and, where configured, hand it the same address each time.
Custom DHCP client IDs
As mentioned, the MAC address is the default client ID, but an administrator (or the device itself) can set a custom identifier using option 61. Some ISPs even require a specific client ID before they will hand out a public address, so this field occasionally needs to be set manually on a router’s WAN connection.
These settings can be accessed through the properties menu of your Network Settings on your PC or the System Preferences through your Mac.
