Chapter 33 DHCP
XS1930 Series User’s Guide
264
33.4 DHCPv4 Relay
Configure DHCP relay on the Switch if the DHCP clients and the DHCP server are not in the same
broadcast domain. During the initial IP address leasing, the Switch helps to relay network information
(such as the IP address and subnet mask) between a DHCP client and a DHCP server. Once the DHCP
client obtains an IP address and can connect to the network, network information renewal is done
between the DHCP client and the DHCP server without the help of the Switch.
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.
33.4.1 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:
33.4.1.1 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.
Table 133 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 134 DHCP Relay Agent Information Option Format
Code
(82)
Length
(N)
i1
i2
...
iN