H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 197)

26-2
Figure 26-1 A typical DHCP application
A DHCP client can get an IP address and other configuration parameters from a DHCP server on
another subnet via a DHCP relay agent. For details about the DHCP relay agent configuration, refer to
DHCP Relay Agent Configuration .
DHCP Address Allocation
Allocation mechanisms
DHCP supports three mechanisms for IP address allocation.
Manual allocation: The network administrator assigns an IP address to a client like a WWW server,
and DHCP conveys the assigned address to the client.
Automatic allocation: DHCP assigns a permanent IP address to a client.
Dynamic allocation: DHCP assigns an IP address to a client for a limited period of time, which is
called a lease. Most DHCP clients obtain their addresses in this way.
Dynamic IP address allocation process
Figure 26-2 Dynamic IP address allocation process
As shown in Figure 26-2 , a DHCP client obtains an IP address from a DHCP server via four steps:
1) The client broadcasts a DHCP-DISCOVER message to locate a DHCP server.
2) A DHCP server offers configuration parameters such as an IP address to the client in a
DHCP-OFFER message. The sending mode of the DHCP-OFFER is determined by the flag field in
the DHCP-DISCOVER message.