UMN:CLI
User Manual
V5824G
296
8.5.7
DHCP Snooping
For enhanced security, the V5824G provides the DHCP snooping feature. The DHCP
snooping filters untrusted DHCP messages and builds/maintains a DHCP snooping
binding table. The untrusted DHCP message is a message received from outside the
network, and an untrusted interface is an interface configured to receive DHCP messages
from outside the network.
The DHCP snooping basically permits all the trusted messages received from within the
network and filters untrusted messages. In case of untrusted messages, all the binding
entries are recorded in a DHCP snooping binding table. This table contains a hardware
address, IP address, lease time, VLAN ID, interface, etc.
It also gives you a way to differentiate between untrusted interfaces connected to the
end-user and trusted interfaces connected to the DHCP server or another switch.
The DHCP snooping only filters the DHCP server message such as a DHCP_OFFER or
DHCP_ACK, which is received from untrusted interfaces.
8.5.7.1
Enabling DHCP Snooping
To enable the DHCP snooping globally, use the following command
Command
Mode
Description
ip dhcp snooping
Global
Enables the DHCP snooping globally.
no ip dhcp snooping
Disables the DHCP snooping globally. (default)
Upon enabling the DHCP snooping, the DHCP_OFFER and DHCP_ACK messages from
all the ports will be discarded before specifying a trusted port.
To enable the DHCP snooping on a VLAN, use the following command
Command
Mode
Description
ip dhcp snooping vlan
VLANS
Global
Enables the DHCP snooping on a specified VLAN.
no ip dhcp snooping vlan
VLANS
Disables the DHCP snooping on a specified VLAN.
You must enable DHCP snooping globally before enabling DHCP snooping on a VLAN.
8.5.7.2
DHCP Trust State
To define a state of a port as trusted or untrusted, use the following command.
Command
Mode
Description
ip dhcp snooping trust
PORTS
Global
Defines a state of a specified port as trusted.
no ip dhcp snooping trust
PORTS
Defines a state of a specified port as untrusted.
(default)
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