3Com Switch 7750 Configuration Guide Guide

580 CHAPTER 55: DHCP RELAY CONFIGURATION
Enabling DHCP Make sure to enable DHCP before you perform other DHCP relay-related
configurations, since other DHCP-related configurations cannot take effect with
DHCP disabled.
Configuring an Interface
to Operate in DHCP
Relay Mode
When an interface operates in the relay mode, the interface forwards the DHCP
packets received from DHCP clients to an external DHCP server, which assigns IP
addresses to the DHCP clients.
To enhance reliability, you can set multiple DHCP servers on the same network.
These DHCP servers form a DHCP server group. When the interface establishes
mapping relationship with the DHCP server group, the interface forwards the
DHCP packets to all servers in the server group.
n
■ You can configure up to eight external DHCP IP addresses in a DHCP server
group.
■ You can map multiple VLAN interfaces to one DHCP server group. But one
VLAN interface can be mapped to only one DHCP server group. If you execute
the dhcp-server groupNo command repeatedly, the new configuration
overwrites the previous one.
■ You need to configure the group number specified in the dhcp-server
groupNo command in VLAN interface view by using the command
dhcp-server groupNo ip ipaddress-address&<1-8> in advance.
Configuring a DHCP
Relay Agent to
Broadcast Responses to
Clients
Generally, the DHCP relay determines to broadcast or unicast responses (including
DHCP-OFFER, DHCP-ACK, or DHCP-NAK) from the DHCP server to the clients
according to the flag field in the DHCP-DISCOVER packet.
■ When the first bit of the flag field is set to 1, the DHCP relay agent broadcasts
the response packets to the clients.
Tabl e 450 Enable DHCP
Operation Command Description
Enter system view system-view -
Enable DHCP dhcp enable
Required
By default, DHCP is enabled
Tabl e 451 Configure an interface to operate in DHCP relay mode
Operation Command Description
Enter system view system-view -
Configure the DHCP server IP
address(es) in a specified
DHCP server group
dhcp-server groupNo ip
ip-address&<1-8>
Required
By default, no DHCP server IP
address is configured in a
DHCP server group
Map an interface to a DHCP
server group
interface interface-type
interface-number
Required
By default, a VLAN interface is
not mapped to any DHCP
server group
dhcp-server groupNo