Chapter 4: Operation of Web-based Management
724-746-5500 | blackbox.com
143
Figure 4-171. DHCP Snooping State.
Parameter description:
VID: When DHCP snooping is enabled on the specified VLAN, DHCP packet filtering will be performed on any un-trusted ports within
the VLAN. It sets an available VLAN ID to enable the DHCP snooping on VLAN interface.
Trust Port 1: If DHCP snooping is enabled globally, and also enabled on the VLAN where the DHCP packet is received, all DHCP
packets are forwarded for a trusted port. It sets a trusted port 1 from 0 to 24. 0 is disabled.
Trust port 2: Sets a trusted port 2 from 0 to 8. 0 is disabled.
Trust VID: Sets a trusted VLAN ID VID from 1 to 4094.
Server IP: Sets a trusted DHCP Server IP address for DHCP Snooping.
Option 82: Sets the DHCP Option 82 function on the switch. The default is Disable.
Action: Sets the switch’s filtering options when its receives a client DHCP request. Options include: keep/drop/replace.
NOTE:
Filtering rules are implemented as follows:
If the DHCP snooping is disabled, all DHCP packets are forwarded.
If DHCP snooping is enabled and also enabled on the VLAN where the DHCP packet is received, all DHCP packets are forwarded to a
trusted port.
If DHCP snooping is enabled on the VLAN where the DHCP packet is received, but the port is not trusted, it processes the packet as
follows:
- If the DHCP packet is a reply packet from a DHCP server, the packet is dropped.
- 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 a server is received on a trusted port, it will be forwarded to both trusted and un-trusted ports in the same
VLAN.
4.19.3 DHCP Snooping Client
Function name: DHCP Snooping Client
Function description:
Shows the DHCP snooping client.