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User’s Manual of SGSD-1022 / SGSD-1022P
SGSW-2840 / SGSW-2840P
323
- DHCP snooping is disabled.
- The request packet contains a valid relay agent address field.
DHCP reply packets received by the relay agent (that is, this switch) are handled in the following way:
1. When the relay agent receives a DHCP reply packet with Option 82 information, it first ensures that the packet is
destined for it, and then removes the Option 82 field from the packet.
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 Managed 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 Managed Switch can discard the Option 82
information, keep the existing information, or replace it with the switch’s relay information.
Figure 4-11-47 DHCP Snooping Information Option Configuration page screenshot
The page includes the following fields:
Object Description
• DHCP Snooping
Information Option
Status
Enables or disables DHCP Option 82 information relay.
(Default: Disabled)
Sets the DHCP snooping information option policy for DHCP client packets that
include Option 82 information.
• Drop
Discards the Option 82 information in a packet and then floods it to
the entire VLAN.
• 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.
• DHCP Snooping
Information Option
Policy
• Replace
Replace the Option 82 information in the client’s request with
information about the relay agent itself, insert the relay agent’s