3Com 5500-EI PWR Reference Manual page 672

Description
Use the dhcp select interface command to configure the specified interface(s) to operate in DHCP
interface address pool mode. Upon receiving a DHCP packet from a DHCP client through an interface
operating in interface address pool mode, the DHCP server chooses an IP address from the interface
address pool of the DHCP server and assigns the address to the DHCP client.
Use the undo dhcp select command to restore the default DHCP packet processing mode.
By default, an interface operates in DHCP server global address pool mode.
Before configuring an interface to operate in DHCP interface address pool mode, you need to configure
an IP address for the interface.
To improve security and avoid malicious attack to the unused SOCKETs, S5500-EI Ethernet switches
provide the following functions:
UDP 67 and UDP 68 ports used by DHCP are enabled only when DHCP is enabled.
UDP 67 and UDP 68 ports are disabled when DHCP is disabled.
The corresponding implementation is as follows:
After a DHCP interface address pool is created by executing the dhcp select interface command,
UDP 67 and UDP 68 ports used by DHCP are enabled.
After a DHCP interface address pool is deleted by executing the undo dhcp select interface
command and all other DHCP functions are disabled, UDP 67 and UDP 68 ports used by DHCP
are disabled accordingly.
Examples
# Enter system view.
<Sysname> system-view
System View: return to User View with Ctrl+Z.
# Configure VLAN-interface 1 through VLAN-interface 3 to operate in DHCP interface address pool
mode, so that when a DHCP packet is received from a DHCP client on one of these interfaces, the
DHCP server assigns an IP address from the corresponding interface DHCP address pool to the DHCP
client.
[Sysname] dhcp select interface interface vlan-interface 1 to vlan-interface 3
# Configure all interfaces to operate in DHCP interface address pool mode, so that when a DHCP
packet is received from a DHCP client through any interface, the DHCP server assigns an IP address in
the interface DHCP address pool to the DHCP client.
[Sysname] dhcp select interface all
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