If the client does not provide a ‘client identifier’ option, the server MUST use the contents of the ‘ chaddr‘ field to identify the client. If the client supplies a ‘client identifier’, the client MUST use the same ‘client identifier’ in all subsequent messages, and the server MUST use that identifier to identify the client. The client MAY choose to explicitly provide the identifier through the ‘ client identifier‘ option. Why this is important in IOS DHCP configurations ? A DHCP server needs to use some unique identifier to associate a client with its lease. For example if your client MAC address is “” then client identifier would be “ ”. In most deployments you can derive client Identifier by adding “ 01” prefix to its hardware address. Usually this is derived from the hardware address. This is the value of the CHADDR (Client Hardware Address) field of the BootP message.Ĭlient Identifier: This is used by DHCP client to identify them-self to DHCP server instead of using CHADDR (hardware address). Hardware Address: It is the MAC address of the client device who is requesting an DHCP IP. There are two terms used in DHCP configuration to identify a client. Defining multiple host pool for each static Hosts. Address reservation under the same DHCP pool configuration.Ģ. There are primarily two ways of doing this.ġ. In this post we will see how we can do this on IOS DHCP server. All other hosts will get dynamically assign IP without having a requirement to keep the same IP all the time.

You may want to have fixed IPs for certain hosts (like printers, BMS devices) without configuring them for static IPs. IP Address reservation is a commonly used feature in any DHCP deployment.

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