3Com Switch 8800 Family Configuration Guide

Configuring DHCP Server 689
Each DHCP address pool can be configured with only one address range. If you
execute the network command multiple times, then only the last configured
address range works.
c
CAUTION: When addresses are obtained through DHCP Relay, the subnet mask of
the normal address pool, the global binding address pool and the Relay address
must be the same. Otherwise, the binding will fail, or the address assigned to the
client will not be in the same network segment with the Relay address.
Forbidding Specified IP
Addresses to Be
Automatically Assigned
You can use the command here to prevent a DHCP server from assigning IP
addresses that are already occupied by such network devices as gateways and file
transfer protocol (FTP) servers to other DHCP clients to avoid IP address conflicts.
Perform the following configuration in system view.
All IP addresses in a DHCP address pool can be automatically assigned by default.
You can set multiple IP address ranges that are not assigned automatically by
executing the dhcp server forbidden-ip command multiple times.
Configuring Lease Time
For DHCP Address Pool
You can configure different lease times for different DHCP address pools. But you
can configure only one lease time for one DHCP address pool and all the address
in the same pool will have the same lease time.
Configuring a lease time for a global DHCP address pool
Perform the following configuration in DHCP address pool view.
Configuring a lease time for current VLAN interface
Perform the following configuration in VLAN interface view.
Tab le 626 Forbid specified IP addresses to be automatically assigned
Operation Command
Forbid specified IP addresses to be
automatically assigned
dhcp server forbidden-ip low-ip-address [
high-ip-address ]
Cancel the forbiddance
undo dhcp server forbidden-ip
low-ip-address [ high-ip-address ]
Tab le 627 Configure a lease time for a global DHCP address pool
Operation Command
Configure a lease time for a global DHCP
address pool
expired { day day [ hour hour [ minute
minute ] ] | unlimited }
Restore the lease time of a global DHCP
address pool to the default value
undo expired
Tab le 628 Configure a lease time for current VLAN interface
Operation Command
Configure a lease time for DHCP address pool
of current VLAN interface
dhcp server expired { day day [ hour hour [
minute minute ] ] | unlimited }
Restore the lease time of DHCP address pool
of current VLAN interface to the default value
undo dhcp server expired