Configuring the Switch
3-92
2. If the DHCP packet’s broadcast flag is on, the reply packet is broadcast to all
attached VLANs, excluding that through which the reply packet was received.
If the DHCP packet’s broadcast flag is off, the switch uses the Option 82
information to identify the interface connected to the requesting client and
unicasts the reply packet to the client.
• DHCP reply packets are flooded onto all attached VLANs other
than the inbound
VLAN under the following situations
:
- The reply packet does not contain Option 82 information.
- The reply packet contains a valid relay agent address field (that is not the
address of this switch) or a zero relay address.
• 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 Option 82
information, 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 – Drop the request packet instead of relaying it.
- Keep – Retain the Option 82 information in the client request, insert the relay
agent’s address (when DHCP snooping is enabled), and unicast the packet to
the DHCP server.
When the Option 82 policy is set to “keep” the original information in the request
packet, the frame type specified (i.e., Remote ID or Circuit ID) is ignored.
- Replace – Replace the Option 82 information in the client’s request with
information about the relay agent itself, insert the relay agent’s address (when
DHCP snooping is enabled), and unicast the packet to the DHCP server. (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 3-48 DHCP Snooping Information Option Configuration
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