H3C Technologies H3C S12500 Series Switches - Manual (Page 40)

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Relay agent option (Option 82)
Option 82 is the relay agent option. It records the location information about the DHCP client. When a
DHCP relay agent device receives a client's request, it adds Option 82 to the request message and sends
it to the server.
The administrator can use Option 82 to locate the DHCP client and further implement security control
and accounting. The DHCP server can use Option 82 to provide individual configuration policies for the
clients.
Option 82 can contain up to 255 sub-options and must have one sub-option at least. Option 82 for a
DHCP relay agent device supports two sub-options: sub-option 1 (Circuit ID) and sub-option 2 (Remote
ID).
Option 82 has no standard definition. Its padding formats vary with vendors.
Circuit ID has the following padding formats:
• String padding format—Contains a character string specified by the user.
• Normal padding format—Contains the VLAN ID and interface number of the interface that
received the client's request.
• Verbose padding format—Contains the access node identifier specified by the user, and the VLAN
ID, interface number and interface type of the interface that received the client's request.
Remote ID has the following padding formats:
• String padding format—Contains a character string specified by the user.
• Normal padding format—Contains the MAC address of the DHCP relay agent interface or the
MAC address of the DHCP snooping device that received the client's request.
• Sysname padding format—Contains the system name of the device. To set the system name for the
device, use the sysname command in system view.
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Option 184
Option 184 is a reserved option. You can define the parameters in the option as needed. The device
supports Option 184 carrying voice related parameters, so a DHCP client with voice functions can get
voice parameters from the DHCP server.
Option 184 has the following sub-options:
• Sub-option 1—Specifies the IP address of the primary network calling processor, which serves as
the network calling control source and provides program download services. For Option 184, you
must define sub-option 1 to make other sub-options take effect.
• Sub-option 2—Specifies the IP address of the backup network calling processor. DHCP clients
contact the backup processor when the primary one is unreachable.
• Sub-option 3—Specifies the voice VLAN ID and the result whether or not the DHCP client takes this
VLAN as the voice VLAN.
• Sub-option 4—Specifies the failover route that includes the IP address and the number of the target
user. A SIP VoIP user uses this IP address and number to directly establish a connection to the target
SIP user when both the primary and backup calling processors are unreachable.
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Protocols and standards
• RFC 2131, Dynamic Host Configuration Protocol
• RFC 2132, DHCP Options and BOOTP Vendor Extensions