Dhcp Snooping Support For Option 82; Recommended Configuration Procedure - HP 1920 Series User Manual

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
DHCP snooping uses the same strategies as the DHCP relay agent to handle Option 82 for DHCP
request messages, as shown in
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

Recommended configuration procedure

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Device Untrusted port
GigabitEthernet
1/0/3 and
Switch B
GigabitEthernet
1/0/4
GigabitEthernet
Switch C
1/0/1
If a DHCP request has... Handling strategy
Drop
Keep
Option 82
Replace
No Option 82 N/A
Task
Enabling DHCP snooping
Configuring DHCP snooping
functions on an interface
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Trusted port disabled from
recording binding entries
GigabitEthernet 1/0/1
GigabitEthernet 1/0/3 and
GigabitEthernet 1/0/4
Table 99. If a response returned by the DHCP server contains Option 82,
The DHCP snooping device...
Drops the message.
Forwards the message without changing Option 82.
Forwards the message after replacing the original
Option 82 with the Option 82 padded in normal
format.
Forwards the message after adding the Option 82
padded in normal format.
Remarks
Required.
By default, DHCP snooping is disabled.
Required.
Specify an interface as trusted and configure DHCP snooping to support
Option 82.
By default, an interface is untrusted and DHCP snooping does not support
Option 82.
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.
308
Trusted port enabled to
record binding entries
GigabitEthernet 1/0/2
GigabitEthernet 1/0/2
"Option 82."