Installation manual

3-119
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Command Usage
• DHCP Snooping (see page 3-117) must be enabled for Option 82 information to be
inserted into request packets.
• When 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.
• If Option 82 is enabled on the switch, information about the switch itself may be included
in any relayed request packet.
• 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. The switch can either drop the DHCP packets, keep the existing
information, or replace it with the switch’s relay information.
Command Attributes
• DHCP Snooping Information Option Status – Enables or disables DHCP Option 82
information relay. (Default: Disabled)
• DHCP Snooping Information Option Policy – Specifies how to handle DHCP client
request packets which already contain Option 82 information.
- Drop – Drops the client’s request packet instead of relaying it.
- Keep – Retains the Option 82 information in the client request, and forwards the
packets to trusted ports.
- Replace – Replaces the Option 82 information in the client’s request with information
about the relay agent itself, inserts the relay agent’s address (when DHCP snooping
is enabled), and forwards the packets to trusted ports. (This is the default policy.)
Web – Click DHCP Snooping, Information Option Configuration. Enable Option 82, and
set the policy for handling request packets, then click Apply.
Figure 3-71 DHCP Snooping Information Option Configuration