Option 82 Supporting - H3C S3600 Series Operation Manual

Operation Manual – DHCP
H3C S3600 Series Ethernet Switches-Release 1510
2) After receiving the packet, the network device providing the DHCP relay function
unicasts the packet to the designated DHCP server based on the configuration.
3) The DHCP server assigns IP addresses and sends the configuration information
to the clients through the DHCP relay so that the clients can be configured
dynamically (the sending mode is decided by the flag filed in the
DHCP-DISCOVER packet, refer to section 1.3 "DHCP Packet Format" for detail).

3.1.3 Option 82 Supporting

I. Introduction to option 82 supporting
Option 82 is a relay agent information option in DHCP packets. When a request packet
from a DHCP client travels through a DHCP relay on its way to the DHCP server, the
DHCP relay adds option 82 into the request packet. Option 82 includes many
sub-options, but the DHCP server supports only sub-option 1 and sub-option 2 at
present. Sub-option 1 defines agent circuit ID (that is, Circuit ID) and sub-option 2
defines remote agent ID (that is, Remote ID).
Option 82 enables a DHCP server to track the address information of DHCP clients and
DHCP relays, through which and other proper software, you can achieve the DHCP
assignment limitation and accounting functions.
II. Primary terminologies
Option: A length-variable field in DHCP packets, carrying information such as part
of the lease information and packet type. It includes at least one option and at
most 255 options.
Option 82: Also known as relay agent information option. This option is a part of
the Option field in DHCP packet. According to RFC3046, option 82 lies before
option 255 and after the other options. Option 82 includes at least one sub-option
and at most 255 sub-options. Currently, the commonly used sub-options in option
82 are sub-option 1, sub-option 2, and sub-option 5.
Sub-option 1: A sub-option of option 82. Sub-option 1 represents the agent circuit
ID, namely Circuit ID. It holds the port number and VLAN-ID of the switch port
connected to the DHCP client, and is usually configured on the DHCP relay.
Generally, sub-option 1 and sub-option 2 must be used together to identify
information about a DHCP source.
Sub-option 2: A sub-option of option 82. Sub-option 2 represents the remote agent
ID, namely Remote ID. This option is usually configured on the DHCP relay, and
defines to carry the MAC address of the DHCP relay in the packet to be sent.
Generally, sub-option 1 and sub-option 2 must be used together to identify
information about a DHCP source.
III. Related specification
The specifications concerning option 82 supporting are as follows:
Chapter 3 DHCP Relay Configuration
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