Client Unique Identifier

Code

61

Length

Variable length; minimum length is 2 octets.

Value

A series of 2 or more octets that is treated as a variable object by the DHCP server. Servers can interpret and use this value to uniquely identify clients.

Description

Used by clients to specify their unique identifier to the server. This option type is most useful for reserved clients. When a reserved client contacts the server, the DHCP service can check and match the client's identifier value to a corresponding identifier used to configure an address reservation in the server's database. When a matching reservation is found, the DHCP server returns the reserved address and its related parameters to the correct client. For this reason, each client's identifier must be unique among all other client identifiers used on the effective DHCP network to which the client is attached (that is, the client's local subnet and any remote subnets reachable using DHCP relay). Vendors and system administrators are responsible for choosing client identifiers that meet this requirement for uniqueness.

One common approach to ensure uniqueness is to configure client reservations at the DHCP server based on the client's media access control address as the client identifier value. Media access control addresses are encoded in the client's network adapter hardware, and are assigned to hardware manufacturers in such as way as to ensure that they are unique for each device.

Structure