3Com S7902E, Руководство по настройке

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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 will fail to assign an address to the client because it cannot assign
an IP address from the father address pool to the client. For the configuration of such address pool,
refer to section 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 will
select 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 will fail to assign addresses to clients. If the IP address of the interface receiving
DHCP requests is 1.1.1.130/25, the DHCP server will select IP addresses for clients from the 1.1.1.0/24
address pool.
Keep the IP addresses for dynamic allocation within the subnet where the interface of the DHCP server
or DHCP relay agent resides to avoid wrong IP address allocation.
IP Address Allocation Sequence
A DHCP server assigns an IP address to a client according to the following sequence:
1) The first assignable IP address found in the extended address pool referenced on the receiving
interface
2) The IP address manually bound to the client’s MAC address or ID
3) The IP address that was ever assigned to the client
4) The IP address designated by the Option 50 field in a DHCP-DISCOVER message
5) The first assignable IP address found in a proper common address pool
6) The IP address that was a conflict or passed its lease duration
If no IP address is assignable, the server does not respond.
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.
DHCP Server Configuration Task List
Complete the following tasks to configure the DHCP server:
Task Remarks
Configuring an Address Pool for the DHCP Server Required
Enabling DHCP Required
Enabling the DHCP Server on an Interface Required