Ip Address Allocation Sequence - HP 10500 Series Configuration Manual

Principles for selecting an address pool
The DHCP server observes the following principles to select an address pool when assigning an IP
address to a client:
If there is an address pool where an IP address is statically bound to the MAC address or ID of the
1.
client, the DHCP server selects this address pool and assigns the statically bound IP address to the
client. For more information, see
If the receiving interface has an extended address pool referenced, the DHCP server assigns an IP
2.
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 more information, see
allocation for an extended address
If neither of the previous situations applies, the DHCP server selects the smallest common address
3.
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 more information, see
"Configuring dynamic address
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
where 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:
IP address statically bound to the client's MAC address or ID.
1.
IP address that was previously assigned to the client.
2.
IP address designated by the Option 50 field in a DHCP-DISCOVER message. Option 50 is the
3.
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.
First assignable IP address found in an extended or common address pool.
4.
IP address that was a conflict or passed its lease duration.
5.
If no IP address is assignable, the server does not respond.
"Configuring static address
pool."
allocation."
37
allocation."
"Configuring dynamic address