A DHCP option is an optional message field that lets clients, servers, and relay agents exchange configuration or process-related information. Common examples include option 3 for the default gateway, option 6 for DNS servers, and option 50 for a requested IP address. About 100 standard options exist, although many are rarely used. section 13.2.2
Option 82 adds relay context that can help a DHCP server make an informed allocation decision. DHCP snooping switches insert it by default, but an untrusted-port request containing option 82 can be discarded. For CCNA configuration, disable insertion unless the switch is a multilayer DHCP relay agent. section 13.2.2
SW2# show ip dhcp snooping . . . Insertion of option 82 is enabled #1 circuit-id default format: vlan-mod-port remote-id: 5254.000c.8b85 (MAC) Option 82 on untrusted port is not allowed #2 . . . #1 Switches insert option 82 into DHCP requests by default. #2 Switches do not accept messages with option 82 on untrusted ports.
Verify whether option 82 insertion is enabled, including the default circuit-ID format and remote-ID. section 13.2.2
Disable option 82 insertion
Use `no ip dhcp snooping information option`, then verify that the status reports “Insertion of option 82 is disabled.” section 13.2.2
