3Com Switch 8800 Advanced Software V5 Configuration Guide

Configuring DHCP Relay Agent 737
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If the DHCP client obtains an IP address via the DHCP relay agent, the address pool
of the subnet which the IP address of the DHCP relay agent belongs to must be
configured on the DHCP server. Otherwise, the DHCP client cannot obtain a
correct IP address.
Correlating a DHCP
Server Group with Relay
Agent Interfaces
To improve reliability, you can specify several DHCP servers as a group on the
DHCP relay agent and correlate a relay agent interface with the server group.
When the interface receives requesting messages from clients, the relay agent will
forward them to all the DHCP servers of the group.
To correlate a DHCP server group with relay agent interfaces, use the following
commands:
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■ You can specify at most twenty DHCP server groups on Switch 8800s .
■ Up to eight DHCP server addresses can be configured for each DHCP server
group. The IP addresses of DHCP servers that belong to the DHCP server group
and those of relay agent’s interfaces cannot be on the same subnet. Otherwise,
the client cannot obtain an IP address.
■ A DHCP server group can correlate with one or multiple DHCP relay agent
interfaces, while a relay agent interface can only correlate with one DHCP
server group. Using the dhcp relay server-select command repeatedly
overwrites the previous configuration. However, if the specified DHCP server
group does not exist, the interface still uses the previous correlation.
■ The group-id in the dhcp relay server-select command was specified by the
dhcp relay server-group command.
Configuring the DHCP
Relay Agent to Send a
DHCP-Release Request
Sometimes, you need to release a client’s IP address manually on the DHCP relay
agent. With this task completed, the DHCP relay agent can actively send a
DHCP-RELEASE request that contains the client’s IP address to be released. Upon
Enable the DHCP relay agent
on the current interface
dhcp select relay Required
With DHCP enabled,
interfaces work in
the DHCP server
mode.
To do... Use the command... Remarks
To do... Use the command... Remarks
Enter system view system-view -
Specify a DHCP server group
number and servers in the
group
dhcp relay server-group group-id ip
ip-address
Required
Not specified by
default
Enter VLAN interface view interface interface-type
interface-number
-
Correlate the DHCP server
group with the current
interface
dhcp relay server-select group-id Required
By default, no
interface is
correlated with any
DHCP server group.