R0106-HP MSR Router Series Layer 3 - IP Services Configuration Guide(V7)

c. If the matching user class has no assignable addresses, the DHCP server matches the client

against the next user class. If all the matching user classes have no assignable addresses, the

DHCP server selects an IP address from the common address range.

d. If the DHCP client does not match any DHCP user class, the DHCP server selects an address in

the IP address range specified by the address range command. If the address range has no

assignable IP addresses or it is not configured, the address allocation fails.

NOTE:

ll address ranges must belong to the primary subnet. If an address range does not reside on the

primary subnet, DHCP cannot assign the addresses in the address range.

• Method 2—Specify a primary subnet and multiple secondary subnets in an address pool.

The DHCP server selects an IP address from the primary subnet first. If there is no assignable IP

address on the primary subnet, the DHCP server selects an IP address from secondary subnets in

the order they are configured.

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 different subnet from 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 on the DHCP server.

• If the IP address of the interface receiving DHCP requests is 1.1.1.1/25 and no address pool is

applied on the interface, the DHCP server selects IP addresses for clients from the address pool

1.1.1.0/25. If no IP address is available in the address pool, the DHCP server will not turn to the

other primary subnets. The address allocation fails.

• If the IP address of the receiving interface is 1.1.1.130/25, the DHCP server selects IP addresses for

clients from the address pool 1.1.1.0/24.