3Com 4200G, 5500G, 4210 manual SwitchA-Vlan-interface1 dhcp select interface

DHCP Relay Agent Configuration Guide 199

[SwitchA-Vlan-interface1] dhcp select interface

# Configure a static IP-to-MAC binding in the DHCP interface address pool.

[SwitchA-Vlan-interface1] dhcp server static-bind ip-address 192.168

.0.10 mac-address 000D-88F7-0001

#Specify the lease duration, DNS server address, and WINS server address in the DHCP interface address pool.

[SwitchA-Vlan-interface1] dhcp server expired day 10

[SwitchA-Vlan-interface1] dhcp server dns-list 192.168.0.20

[SwitchA-Vlan-interface1] dhcp server nbns-list 192.168.0.30

[SwitchA-Vlan-interface1] quit

Complete Configuration #

interface Vlan-interface1

ip address 192.168.0.1 255.255.255.0 dhcp select interface

dhcp server static-bind ip-address 192.168.1.10 mac-address 000d-88 f7-0001

dhcp server dns-list 192.168.0.20 dhcp server nbns-list 192.168.0.30 dhcp server expired day 10

#

dhcp server forbidden-ip 192.168.0.10 dhcp server forbidden-ip 192.168.0.20 dhcp server forbidden-ip 192.168.0.30

#

Precautions After all the addresses in the interface address pool have been assigned, the DHCP server looks up IP addresses from the global address pool containing the network segment of the interface address pool for the DHCP clients. As a result, the IP addresses obtained from the global address pool and those obtained from the interface address pool are not on the same network segment, so the clients cannot communicate with each other.

In this example, the number of clients requesting IP addresses from VLAN-interface 1 is recommended to be less than or equal to 250.

DHCP Relay Agent Since some DHCP packets are broadcast, DHCP is only applicable to the situation

Configuration Guide where DHCP clients and the DHCP server are in the same network segment, that is, you need to deploy at least one DHCP server for each network segment, which is not economical.

DHCP relay agent is designed to address this problem. It enables DHCP clients in a subnet to communicate with the DHCP server in another subnet to obtain IP addresses. In this way, the DHCP clients in multiple networks can use the same DHCP server, which is cost-effective and allows for centralized management.