CLI Reference Guide-R04

Chapter 9 | General Security Measures
DHCPv4 Snooping
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switch receives any messages from a DHCP server, any packets received from
untrusted ports are dropped.
Example
This example enables DHCP snooping globally for the switch.
Console(config)#ip dhcp snooping
Console(config)#
Related Commands
ip dhcp snooping vlan (333)
ip dhcp snooping trust (336)
ip dhcp snooping
information option
This command enables the use of DHCP Option 82 information for the switch, and
specifies the frame format to use for the remote-id when Option 82 information is
generated by the switch. Use the no form to disable this function.
Syntax
[no] ip dhcp snooping information option
no ip dhcp snooping information option
Default Setting
Option 82: Disabled
Command Mode
Global Configuration
Command Usage
◆ 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 82 is enabled, the requesting
client (or an intermediate relay agent that has used the information fields to
describe itself) can be identified in the DHCP request packets forwarded by the
switch and in reply packets sent back from the DHCP server.
◆ 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.