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Configuring the Switch
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Web – Click DHCP Snooping, VLAN Configuration.
Figure 3-145 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 drop the DHCP packets, 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.
Command Attributes
• DHCP Snooping Information Option Status – Enables or disables DHCP Option
82 information relay.
• DHCP Snooping Information Option Policy – Sets the DHCP snooping
information option policy for DHCP client packets that include Option 82
information.
• Replace – Overwrites the DHCP client packet information with the switch’s relay
information.
• Keep – Retains the client’s DHCP information.
• Drop – Discards the Option 82 information in a packet and then floods it to the
entire VLAN.
Console(config)#ip dhcp snooping vlan 1 4-319
Console(config)#