ZyXEL Communications XMG1915 Series - Dhcpv4 Relay Agent Information

Chapter 51 DHCP
XMG1915 Series User’s Guide
292
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:
51.3.1.1 DHCPv4 Relay Agent Information Format
A DHCP Relay Agent Information option has the following format.
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.
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.
Table 159 Relay Agent Information
FIELD LABELS DESCRIPTION
Slot ID (1 byte) This value is always 0 for stand-alone switches.
Port ID (1 byte) This is the port that the DHCP client is connected to.
VLAN ID (2 bytes) This is the VLAN that the port belongs to.
Information (up to 64 bytes) This optional, read-only field is set according to system name set in
SYSTEM > General Setup.
Table 160 DHCP Relay Agent Information Option Format
Code
(82)
Length
(N)
i1 i2
...
iN
Table 161 DHCP Relay Agent Circuit ID Sub-option Format
SubOpt Code Length Value
1
(1 byte)
N
(1 byte)
Slot ID, Port ID, VLAN ID, System Name or String
Table 162 DHCP Relay Agent Remote ID Sub-option Format
SubOpt Code Length Value
2
(1 byte)
N
(1 byte)
MAC Address or String