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Option 82 contains two common sub-options: Circuit ID and Remote ID. Circuit ID is mainly used to identify the VLAN and the interface of the client, Remote ID identifies the device from which the client accessed, usually the MAC address of the device.

Packet Format

Circuit ID Sub-option

Circuit ID includes three types: Type 0 (value is port index), Type 1 (value is port name + VLAN ID) and Type 2 (value is port description + VLAN ID). The format is listed below by types.

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DHCP snooping Option 82 can be enabled on Switch 1, and DHCP relay Option 82 can be enabled on Switch 2. It is optional. But if Option 82 is inserted on Switch 1, DHCP relay Option 82 trust all should be enabled on Switch 2.

Option 12 and Option 42

Info
titleNOTE:
  • Option 12 and Option 42 are only supported in PICOS 4.4.4.3.
  • When in-band and out-of-band DHCP are enabled together, the hostname will be the last one received from the DHCP server.
  • The system hostname obtained via the DHCP option will not change when lease expires and DHCP server service is stopped.
  • If the device has a statically configured hostname via the CLI, this hostname will take precedence over the one obtained from DHCP. If there is no statically configured hostname, the device will use the hostname obtained from the DHCP server.
  • The NTP service will quit after deleting all the NTP server IP addresses via the PICOS CLI, which will result in NTP service becoming unavailable.
  • The NTP service, initiated via the DHCP option, will quit when lease expires and DHCP server service is stopped. 
  • When using the DHCP option to obtain NTP servers via in-band, and the eth0 port (with DHCP enabled) is down, a static IP address must be set for the eth0 port; otherwise, the NTP service cannot function normally.
  • Support both statically configuring NTP servers via the PICOS CLI and dynamically obtaining them from DHCP.

DHCP options are additional parameters that can be passed from a DHCP server to DHCP clients during the IP address assignment process. These options provide additional configuration information beyond just the IP address and subnet mask. In addition to supporting Option 82, PICOS also supports Option 12 and Option 42.

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Option 12: This option is used to specify the hostname of the DHCP client. When a DHCP client requests an IP address from a DHCP server, it can include its hostname in the DHCP request message using Option 12. The DHCP server can then use this information to assign a hostname to the client along with its IP address lease.

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Interaction with Other Protocols

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