DHCP address pool

Each DHCP address pool has a group of assignable IP addresses and network configuration parameters. The DHCP server selects IP addresses and other parameters from the address pool and assigns them to the DHCP clients.

Address assignment mechanisms

Configure the following address assignment mechanisms as needed:

You can specify IP address ranges in an address pool by using either of the following methods:

Principles for selecting an address pool

The DHCP server observes the following principles to select an address pool for a client:

  1. If there is an address pool where an IP address is statically bound to the MAC address or ID of the client, the DHCP server selects this address pool and assigns the statically bound IP address and other configuration parameters to the client.

  2. If the receiving interface has an address pool applied, the DHCP server selects an IP address and other configuration parameters from this address pool.

  3. If no static address pool is configured and no address pool is applied to the receiving interface, the DHCP server selects an address pool depending on the client location.

    • Client on the same subnet as the server—The DHCP server compares the IP address of the receiving interface with the primary subnets of all address pools.

      • If a match is found, the server selects the address pool with the longest-matching primary subnet.

      • If no match is found, the DHCP server compares the IP address with the secondary subnets of all address pools. The server selects the address pool with the longest-matching secondary subnet.

    • Client on a different subnet than the server—The DHCP server compares the IP address in the giaddr field of the DHCP request with the primary subnets of all address pools.

      • If a match is found, the server selects the address pool with the longest-matching primary subnet.

      • If no match is found, the DHCP server compares the IP address with the secondary subnets of all address pools. The server selects the address pool with the longest-matching secondary subnet.

For example, two address pools 1.1.1.0/24 and 1.1.1.0/25 are configured but not applied to any DHCP server's interfaces.

To ensure correct address allocation, keep the IP addresses used for dynamic allocation on one of the subnets: