3Com Switch 8800 Family Configuration Guide

Configuring General DHCP 685
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CAUTION: The dhcp select interface command cannot be used together with
the ip relay address or dhcp relay security address-check enable command.
Perform the following configuration in system view to configure the processing
method of DHCP packets for multiple VLAN interfaces.
By default, DHCP packets are processed in global method. That is, DHCP packets
are forwarded to local DHCP server and IP addresses in global address pools are
assigned.
Enabling/Disabling Fake
DHCP Server Detection
If an unauthorized DHCP server exists in a network, it also answers when users in
the network request IP addresses, and then interacts with the DHCP clients. This
causes that the users cannot obtain correct IP addresses to access network. This
kind of DHCP servers are known as fake DHCP servers.
With fake DHCP server detection enabled, the switch can record information (such
as the IP addresses) about the DHCP servers. This helps administrators to detect
fake DHCP servers in time and take proper measures.
Perform the following configuration in system view.
Tab le 619 Configure the processing method for current VLN interface
Operation Command
Specify to forward DHCP packets to local DHCP server and let the
local server assign IP addresses in global address pools to DHCP
clients
dhcp select global
Specify to forward DHCP packets to local DHCP server and let the
local server assign IP addresses in VLAN interface address pool to
DHCP clients
dhcp select interface
Specify to forward DHCP packets to remote DHCP servers. In this
case, the current switch operates as a DHCP relay, and IP addresses
are assigned by DHCP servers located in other networks
dhcp select relay
Revert to the default processing mode undo dhcp select
Tab le 620 Configure the processing method for multiple VLAN interfaces
Operation Command
Specify to forward DHCP packets to local
DHCP server and let the local server assign IP
addresses in global address pools to DHCP
clients
dhcp select global { interface
vlan-interface vlan-id [ to vlan-interface
vlan-id ] | all }
Specify to forward DHCP packets to local
DHCP server and let the local server assign IP
addresses in VLAN interface address pool to
DHCP clients
dhcp select interface { interface
vlan-interface vlan-id [ to vlan-interface
vlan-id ] | all }
Specify to forward DHCP packets to remote
DHCP servers. In this case, the current switch
operates as a DHCP relay, and IP addresses are
assigned by DHCP servers located in other
networks
dhcp select relay { interface vlan-interface
vlan-id [ to vlan-interface vlan-id ] | all }
Revert to the default processing mode
undo dhcp select { interface vlan-interface
vlan-id [ to vlan-interface vlan-id ] | all }