Dhcpv4 Relay Agent Information - ZyXEL Communications XMG1915 Series User Manual

51.3.1 DHCPv4 Relay Agent Information

The Switch can add information about the source of client DHCP requests that it relays to a DHCP server
by adding Relay Agent Information. This helps provide authentication about the source of the requests.
The DHCP server can then provide an IP address based on this information. Please refer to RFC 3046 for
more details.
The DHCP Relay Agent Information feature adds an Agent Information field (also known as the Option
82 field) to DHCP requests. The Option 82 field is in the DHCP headers of client DHCP request frames that
the Switch relays to a DHCP server.
Relay Agent Information can include the System Name of the Switch if you select this option. You can
change the System Name in SYSTEM > General Setup.
The following describes the DHCP relay agent information that the Switch sends to the DHCP server:
Table 159 Relay Agent Information
FIELD LABELS
Slot ID
Port ID
VLAN ID
Information
51.3.1.1 DHCPv4 Relay Agent Information Format
A DHCP Relay Agent Information option has the following format.
Table 160 DHCP Relay Agent Information Option Format
Code
(82)
i1, i2 and iN are DHCP relay agent sub-options, which contain additional information about the DHCP
client. You need to define at least one sub-option.
51.3.1.2 Sub-Option Format
There are two types of sub-option: "Agent Circuit ID Sub-option" and "Agent Remote ID Sub-option".
They have the following formats.
Table 161 DHCP Relay Agent Circuit ID Sub-option Format
SubOpt Code
1
(1 byte)
Table 162 DHCP Relay Agent Remote ID Sub-option Format
SubOpt Code
2
(1 byte)
The 1 in the first field identifies this as an Agent Circuit ID sub-option and two identifies this as an Agent
Remote ID sub-option. The next field specifies the length of the field.
Chapter 51 DHCP
DESCRIPTION
(1 byte) This value is always 0 for stand-alone switches.
(1 byte) This is the port that the DHCP client is connected to.
(2 bytes) This is the VLAN that the port belongs to.
(up to 64 bytes) This optional, read-only field is set according to system name set in
SYSTEM > General Setup.
Length i1
(N)
Length
N Slot ID, Port ID, VLAN ID, System Name or String
(1 byte)
Length
N MAC Address or String
(1 byte)
XMG1915 Series User's Guide
i2 iN
...
Value
Value
292