R3303-HP HSR6800 Routers Layer 3 - IP Services Configuration Guide

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 to the

client. For the configuration of this address pool, see "Configuring static address allocation."

2. If the rec

eiving interface has an extended address pool referenced, the DHCP server assigns an IP

address from this address pool. If no IP address is available in the address pool, the DHCP server

fails to assign an address to the client. For the configuration of such an address pool, see

"Configuring dynamic address allocation for an extended address p

ool."

3. Otherwise, the DHCP server selects the smallest common address pool that contains the IP address

of the receiving interface (if the client and the server reside on the same subnet), or the smallest

common address pool that contains the IP address specified in the giaddr field of the client's

request (if a DHCP relay agent is in-between). If no IP address is available in the address pool, the

DHCP server fails to assign an address to the client because it cannot assign an IP address from the

parent address pool to the client. For the configuration of such an address pool, see "Configuring

dynamic

address allocation."

For example, two common 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, the DHCP server selects IP

addresses for clients from address pool 1.1.1.0/25. If no IP address is available in the address pool, the

DHCP server fails to assign addresses to clients. If the IP address of the interface receiving DHCP requests

is 1.1.1.130/25, the DHCP server selects IP addresses for clients from the 1.1.1.0/24 address pool.

NOTE:

To avoid wrong IP address allocation, keep the IP addresses for dynamic allocation within the subnet

here the interface of the DHCP server or DHCP relay agent resides.

IP address allocation sequence

A DHCP server assigns an IP address to a client in the following sequence:

1. IP address statically bound to the client's MAC address or ID.

2. IP address that was ever assigned to the client.

3. IP address designated by the Option 50 field in a DHCP-DISCOVER message.

Option 50 is the requested IP address field in DHCP-DISCOVER messages. It is padded by the

client to specify the IP address that the client wants to obtain. The contents to be padded depend

on the client.

4. First assignable IP address found in an extended or common address pool.

5. IP address that was a conflict or passed its lease duration.

If no IP address is assignable, the server does not respond.

DHCP server configuration task list

Task Remarks

Configuring an address pool on the DHCP server Required.

Enabling DHCP Required.

Enabling the DHCP server on an interface Required.