3Com Switch 7750 Configuration Guide Guide

55
DHCP RELAY CONFIGURATION
Introduction to DHCP
Relay
Usage of DHCP Relay Since the packets are broadcasted in the process of obtaining IP addresses, DHCP
is only applicable to the situation that DHCP clients and DHCP servers are in 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 in a
subnet to communicate with the DHCP server in another subnet so that the DHCP
clients can obtain IP addresses. In this case, the DHCP clients in multiple networks
can use the same DHCP server, which can decrease your cost and provide a
centralized administration.
DHCP Relay
Fundamentals
Figure 147 illustrates a typical DHCP relay application.
Figure 147 Typical DHCP relay application
DHCP relays can transparently transmit broadcast packets on DHCP clients or
servers to the DHCP servers or clients in other network segments.
In the process of dynamic IP address assignment through the DHCP relay, the
DHCP client and DHCP server interoperate with each other in a similar way as they
do without the DHCP relay. The following sections only describe the forwarding
process of the DHCP relay. For the interaction process of the packets, see
“Obtaining IP Addresses Dynamically”.
1 The DHCP client broadcasts the DHCP-DISCOVER packet.
2 After receiving the packets, the network device providing the DHCP relay function
unicasts the packet to the designated DHCP server based on the configuration.
Eth er n et Inter net
DHCP
client
DHCP clientDHCP client
DHCP client
Sw itch ( DHCP relay
)
DHC P ser v er
Eth er n et Inter net
DHCP
client
DHCP clientDHCP client
DHCP client
)
Eth er n et Inter net
DHCP
client
DHCP clientDHCP client
DHCP client
Sw itch ( DHCP relay
)
DHC P ser v er
Eth er n et Inter net
DHCP
client
DHCP clientDHCP client
DHCP client
)
Eth er n et Inter net
DHCP
client
DHCP clientDHCP client
DHCP client
Sw itch ( DHCP relay
)
DHC P ser v er
Eth er n et Inter net
DHCP
client
Eth er n et Inter net
DHCP
client
DHCP clientDHCP client
DHCP client
Sw itch ( DHCP relay
)
DHC P ser v er
Eth er n et Inter net
DHCP
client
DHCP clientDHCP client
DHCP client
)