Configuring the Switch
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DHCP Snooping VLAN Configuration
Enables DHCP snooping on the specified VLAN.
Command Attributes
• VLAN ID – ID of a configured VLAN. (Range: 1-4094)
• DHCP Snooping Status – Enables or disables DHCP snooping for the selected
VLAN. When DHCP snooping is enabled globally on the switch, and enabled on
the specified VLAN, DHCP packet filtering will be performed on any untrusted ports
within the VLAN.
Web – Click DHCP Snooping, VLAN Configuration.
Figure 3-115 DHCP Snooping VLAN Configuration
CLI – This example first enables DHCP Snooping for VLAN 1.
DHCP Snooping Information Option Configuration
DHCP provides a relay mechanism for sending information about the switch and its
DHCP clients to the DHCP server. Known as DHCP Option 82, it allows compatible
DHCP servers to use the information when assigning IP addresses, or to set other
services or policies for clients.
When the DHCP Snooping Information Option is enabled, clients can be identified
by the switch port to which they are connected rather than just their MAC address.
DHCP client-server exchange messages are then forwarded directly between the
server and client without having to flood them to the entire VLAN.
In some cases, the switch may receive DHCP packets from a client that already
includes DHCP Option 82 information. The switch can be configured to set the
action policy for these packets. Either the switch can discard the DHCP information,
keep the existing information, or replace it with the switch’s relay information.
Note:
DHCP snooping must be enabled on the switch for the DHCP Option 82
information to be inserted into packets.
Console(config)#ip dhcp snooping vlan 1 4-233
Console(config)#
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