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Configuring an Option 82 Prefix

You can include an optional prefix to the base option 82 information in DHCP packets destined for a DHCP server.

The prefix is separated from the option 82 agent-circuit-id information by a colon (:), and can include any combination of the host-name, logical-system-name, and routing-instance-name options. The DHCP relay agent obtains the values for the host-name, logical-system-name, and routing-instance-name as follows:

  • If you include the host-name option, the DHCP relay agent uses the hostname of the router configured with the host-name statement at the [edit system] hierarchy level.
  • If you include the logical-system-name option, the DHCP relay agent uses the logical system name configured with the logical-system statement at the [edit logical-system] hierarchy level.
  • If you include the routing-instance-name option, the DHCP relay agent uses the routing instance name configured with the routing-instance statement at the [edit routing-instances] hierarchy level or at the [edit logical-system logical-system-name routing-instances] hierarchy level.

If you include the hostname and either or both of the logical system name and the routing instance name in the prefix, the hostname is followed by a forward slash (/). If you include both the logical system name and the routing instance name in the prefix, these values are separated by a semicolon (;).

The following examples show several possible formats for the agent-circuit-id information when you specify the prefix statement for Fast Ethernet (fe) or Gigabit Ethernet (ge) interfaces with S-VLANs.

  • If you include only the hostname in the prefix for Fast Ethernet or Gigabit Ethernet interfaces with S-VLANs:
    hostname:(fe | ge)-fpc/pic/port:svlan-id-vlan-id
  • If you include only the logical system name in the prefix for Fast Ethernet or Gigabit Ethernet interfaces with S-VLANs:
    logical-system-name:(fe | ge)-fpc/pic/port:svlan-id-vlan-id
  • If you include only the routing instance name in the prefix for Fast Ethernet or Gigabit Ethernet interfaces with S-VLANs:
    routing-instance-name:(fe | ge)-fpc/pic/port:svlan-id-vlan-id
  • If you include both the hostname and the logical system name in the prefix for Fast Ethernet or Gigabit Ethernet interfaces with S-VLANs:
    host-name/logical-system-name:(fe | ge)-fpc/pic/port:svlan-id-vlan-id
  • If you include both the logical system name and the routing instance name in the prefix for Fast Ethernet or Gigabit Ethernet interfaces with S-VLANs:
    logical-system-name;routing-instance-name:(fe | ge)-fpc/pic/port:svlan-id-vlan-id
  • If you include the hostname, logical system name, and routing instance name in the prefix for Fast Ethernet or Gigabit Ethernet interfaces with S-VLANs:
    host-name/logical-system-name;routing-instance-name:(fe | ge)-fpc/pic/port:svlan-id-vlan-id

For Fast Ethernet or Gigabit Ethernet interfaces that use VLANs but not S-VLANs, only the vlan-id value appears in the agent-circuit-id format. For Fast Ethernet or Gigabit Ethernet interfaces that do not use VLANs or S-VLANs, neither the vlan-id value nor the svlan-id value appears.

To configure an optional prefix with the option 82 information:

  1. Specify that you want to configure option 82 support.
    [edit forwarding-options dhcp-relay]
    user@host# edit relay-option-82
  2. Specify insertion of the agent-circuit id.
    [edit forwarding-options dhcp-relay relay-option-82]
    user@host# set circuit-id
  3. Specify that the prefix is included in the option 82 information. In this example, the prefix includes the hostname and logical system name
    [edit forwarding-options dhcp-relay relay-option-82]
    user@host# set circuit-id prefix host-name logical-system-name