H3C Technologies H3C S12500 Series Switches - Manual (Page 42)

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Configuring the DHCP server
The DHCP server configuration is supported only on Layer 3 Ethernet interfaces (or subinterfaces), VLAN
interfaces, Layer 3 aggregate interfaces, and loopback interfaces.
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Overview
The DHCP server is well suited to networks where:
• Manual configuration and centralized management are difficult to implement.
• IP addresses are limited. For example, an ISP limits the number of concurrent online users, and users
must acquire IP addresses dynamically.
• Most hosts do not need fixed IP addresses.
In addition to assigning IP addresses to DHCP clients on a public network, an MCE serving as the DHCP
server can also assign IP addresses to DHCP clients on private networks. The IP address ranges of public
and private networks or those of private networks on the DHCP server cannot overlap each other. For
more information about MCE, see MPLS Configuration Guide.
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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.
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Address assignment mechanisms
Configure the following address assignment mechanisms as needed:
• Static address allocation—Manually bind the MAC address or ID of a client to an IP address in a
DHCP address pool. When the client requests an IP address, the DHCP server assigns the IP
address in the static binding to the client.
• Dynamic address allocation—Specify IP address ranges in a DHCP address pool. Upon receiving
a DHCP request, the DHCP server dynamically selects an IP address from the matching IP address
range in the address pool.
There are two methods to specify IP address ranges in an address pool:
• Method 1—Specify a primary subnet in an address pool and divide the subnet into multiple
address ranges, which include a common IP address range and IP address ranges for DHCP user
classes.
Upon receiving a DHCP request, the DHCP server finds a user class matching the client and selects
an IP address in the address range of the user class for the client. A user class can include multiple
matching rules, and a client matches the user class as long as it matches any of the rules. In
address pool view, you can specify different address ranges for different user classes.
DHCP selects an IP address for a client in the following order:
a. DHCP matches the client against DHCP user classes in the order they are configured.
b. If the client matches a user class, the DHCP server selects an IP address from the address range
of the user class.