General Security Measures
3-105
3
* If the DHCP packet is from a client, such as a DECLINE or RELEASE
message, the switch forwards the packet only if the corresponding entry is
found in the binding table.
* 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 is from 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.
DHCP Snooping Configuration
Use the DHCP Snooping Configuration page to enable DHCP Snooping globally on
the switch, or to configure MAC Address Verification.
Command Attributes
•
DHCP Snooping Status –
Enables DHCP snooping globally. (Default: Disabled)
•
DHCP Snooping MAC-Address Verification
– Enables or disables MAC address
verification. If the source MAC address in the Ethernet header of the packet is not
same as the client's hardware address in the DHCP packet, the packet is dropped.
Web
– Click DHCP Snooping, Configuration. Select the required options and click
Apply.
Figure 3-64 DHCP Snooping Configuration
Summary of Contents for DG-GS1550
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Page 46: ...Initial Configuration 2 10 2 ...
Page 642: ...Command Line Interface 4 342 4 ...
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