3Com 4200G 12-Port, Руководство по настройке

Страница: 407 / 422

46
DHCP R
ELAY
C
ONFIGURATION
Introduction to DHCP
Relay
Usage of DHCP Relay Early DHCP implementations assumes that DHCP clients and DHCP servers are on the
same network segment, that is, you need to deploy at least one DHCP server for each
network segment, which is far from economical.
DHCP Relay is designed to address this problem. It enables DHCP clients of multiple
networks to share a common DHCP server, through which DHCP clients in a LAN can
acquire IP addresses by negotiating with DHCP servers of other networks. It decreases
your cost and provides a centralized administration.
A DHCP relay can be a host or a switch that has DHCP relay service enabled.
DHCP Relay
Fundamentals
Figure 123 illustrates a typical DHCP relay application.
Figure 123 Typical DHCP relay application
A DHCP relay works as follows:
■
A DHCP client broadcasts a configuration request packet in the local network
when it starts and initiates.
■
If a DHCP server exists in the local network, it processes the configuration request
packet directly without the help of a DHCP relay.
■
If no DHCP server exists in the local network, the network device serving as a
DHCP relay on this network appropriately processes the configuration request
packet and forwards it to a specified DHCP server located on another network.
■
When the DHCP server receives the packet, it generates configuration information
accordingly and sends it to the DHCP client through the DHCP relay to complete
the dynamic configuration of the DHCP client.
Ethernet Internet
DHCP
client
DHCP client DHCP client
DHCP client
Sw itch ( DHCP relay
)
DHCP server
Ethernet Internet
DHCP
client
DHCP client DHCP client
DHCP client
)
Ethernet Internet
DHCP
client
DHCP client DHCP client
DHCP client
Sw itch ( DHCP relay
)
DHCP server
Ethernet Internet
DHCP
client
DHCP client DHCP client
DHCP client
)
Ethernet Internet
DHCP
client
DHCP client DHCP client
DHCP client
Sw itch ( DHCP relay
)
DHCP server
Ethernet Internet
DHCP
client
Ethernet Internet
DHCP
client
DHCP client DHCP client
DHCP client
Sw itch ( DHCP relay
)
DHCP server
Ethernet Internet
DHCP
client
DHCP client DHCP client
DHCP client
)