HP manual 321

Device	Untrusted port	Trusted port disabled from	Trusted port enabled to
		recording binding entries	record binding entries
	GigabitEthernet
Switch B	1/0/3 and	GigabitEthernet 1/0/1	GigabitEthernet 1/0/2
	GigabitEthernet
	1/0/4
Switch C	GigabitEthernet	GigabitEthernet 1/0/3 and	GigabitEthernet 1/0/2
	1/0/1	GigabitEthernet 1/0/4

DHCP snooping support for Option 82

Option 82 records the location information about the DHCP client so the administrator can locate the DHCP client for security and accounting purposes. For more information, see "Option 82."

DHCP snooping uses the same strategies as the DHCP relay agent to handle Option 82 for DHCP request messages, as shown in Table 99. If a response returned by the DHCP server contains Option 82, DHCP snooping removes Option 82 before forwarding the response to the client. If the response contains no Option 82, DHCP snooping forwards it directly.

Table 99 Handling strategy

If a DHCP request has…	Handling strategy	The DHCP snooping device…
	Drop	Drops the message.
	Keep	Forwards the message without changing Option 82.
Option 82
		Forwards the message after replacing the original
	Replace	Option 82 with the Option 82 padded in normal
		format.
No Option 82	N/A	Forwards the message after adding the Option 82
		padded in normal format.

Recommended configuration procedure

Task	Remarks
Enabling DHCP snooping	Required.
	By default, DHCP snooping is disabled.
	Required.
	Specify an interface as trusted and configure DHCP snooping to support
	Option 82.
Configuring DHCP snooping	By default, an interface is untrusted and DHCP snooping does not support
	Option 82.
functions on an interface
	IMPORTANT:
	You need to specify the ports connected to the authorized DHCP servers as
	trusted to make sure DHCP clients can obtain valid IP addresses. The trusted
	port and the port connected to the DHCP client must be in the same VLAN.
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