Operation Manual – DHCP
H3C S5600 Series Ethernet Switches
Chapter 3 DHCP Relay Agent Configuration
3-2
Figure 3-1
Typical DHCP relay agent application
In the process of dynamic IP address assignment through the DHCP relay agent, the
DHCP client and DHCP server interoperate with each other in a similar way as they do
without the DHCP relay agent. The following sections only describe the forwarding
process of the DHCP relay agent. For the interaction process of the packets, see
section
Obtaining IP Addresses Dynamically
.
1) After receiving the DHCP-DISCOVER or DHCP-REQUEST broadcast from the
client, the network device providing the DHCP relay agent function unicasts the
message to the designated DHCP server based on the configuration.
2) The DHCP server selects an IP address and other parameters and sends the
configuration information to the DHCP relay agent that relays the information to
the client (the sending mode is decided by the flag filed in the client’s
DHCP-DISCOVER packet, refer to section
DHCP Packet Format
for details).
3.1.3 Option 82 Support on DHCP Relay Agent
I. Introduction to Option 82
Option 82 is the relay agent information option in the DHCP message. It records the
location information of the DHCP client. With this option, the administrator can locate
the DHCP client to further implement security control and accounting. The Option 82
supporting server can also use such information to define individual assignment
policies of IP address and other parameters for the clients.
Option 82 involves at most 255 sub-options. If Option 82 is defined, at least one
sub-option must be defined. Currently the DHCP relay agent supports two sub-options:
sub-option 1 (circuit ID sub-option) and sub-option 2 (remote ID sub-option).
II. Padding content of Option 82
Option 82 has no unified definition in RFC 3046. Its padding information varies with
vendors. Currently, S5600 Series Ethernet Switches that operate as DHCP relay
agents support the extended padding format of Option 82 sub-options. By default, the
