User manual

Chapter 41 DHCP
GS2210 Series User’s Guide
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The Switch can be configured as a global DHCP relay. This means that the Switch forwards all DHCP
requests from all domains to the same DHCP server. You can also configure the Switch to relay DHCP
information based on the VLAN membership of the DHCP clients.
41.4.1 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 Basic Settings > General Setup.
The following describes the DHCP relay agent information that the Switch sends to the DHCP server:
41.4.1.1 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.
41.4.1.2 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 167 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 Basic
Settings > General Setup.
Table 168 DHCP Relay Agent Information Option Format
Code
(82)
Length
(N)
i1 i2
...
iN
Table 169 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