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Chapter 4: Web configuration
158 NS3562-8P-2S User Manual
• If the DHCP packet is from a client, such as a DISCOVER, REQUEST, INFORM,
DECLINE or RELEASE message, the packet is forwarded if MAC address
verification is disabled. However, if MAC address verification is enabled, then the
packet will only be forwarded if the client’s hardware address stored in the DHCP
packet is the same as the source MAC address in the Ethernet header.
• If the DHCP packet is not a recognizable type, it is dropped.
• If a DHCP packet from a client passes the filtering criteria above, it will only be
forwarded to trusted ports in the same VLAN.
• If a DHCP packet from a server is received on a trusted port, it will be forwarded to
both trusted and untrusted ports in the same VLAN.
• If the DHCP snooping is globally disabled, all dynamic bindings are removed from
the binding table.
Additional considerations when the switch itself is a DHCP client:
• The port(s) through which the switch submits a client request to the DHCP server
must be configured as trusted. Note that the switch will not add a dynamic entry for
itself to the binding table when it receives an ACK message from a DHCP server.
• Also, when the switch sends out DHCP client packets for itself, no filtering takes
place. However, when the switch receives any messages from a DHCP server, any
packets received from untrusted ports are dropped.
Global setting
Configure DHCP Snooping on the DHCP Snooping Configuration page.
The page includes the following fields:
Object Description
DHCP Snooping Indicates the DHCP snooping mode operation. Possible modes are:
Enabled : Enable DHCP snooping mode operation.
When enable DHCP snooping mode operation, the request DHCP
messages will be forwarded to trusted ports and only allowed reply packets
from trusted ports.
Disabled : Disable DHCP snooping mode operation.
Buttons
• Click Apply to apply changes.
DHCP snooping VLAN setting
When DHCP snooping is enabled globally on the switch, and enabled on the specified
VLAN, DHCP packet filtering will be performed on any untrusted ports within the VLAN.