ZyXEL Communications GS1920-48HPv2, Руководство пользователя

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Chapter 37 DHCP
GS1920v2 Series User’s Guide
325
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.
37.4.1 DHC Pv4 Re la y Ag e nt Info rm a tio n
The Switch can add information about the source of client DHCP requests that it relays to a DHCP server
by adding
Re la y Ag e nt Info rm a tio n
. 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
Re la y Ag e nt Info rm a tio n
feature adds an Agent Information field (also known as the
O ptio n
82
field) to DHCP requests. The
O ptio n 82
field is in the DHCP headers of client DHCP request frames that
the Switch relays to a DHCP server.
Re la y Ag e nt Info rm a tio n
can include the
Syste m Na m e
of the Switch if you select this option. You can
change the
Syste m Na m e
in
Ba sic Se tting s
>
G e ne ra l Se tup
.
The following describes the DHCP relay agent information that the Switch sends to the DHCP server:
37.4.1.1 DHC Pv4 Re la y Ag e nt Info rm a tio n Fo rm a t
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.
37.4.1.2 Sub - O ptio n Fo rm a t
There are two types of sub-option: “Agent Circuit ID Sub-option” and “Agent Remote ID Sub-option”.
They have the following formats.
Table 153 Relay Agent Information
FIELD LABELS DESC RIPTIO N
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
Ba sic
Se tting s > G e ne ra l Se tup
.
Table 154 DHCP Relay Agent Information Option Format
Code
(82)
Length
(N)
i1 i2
...
iN
Table 155 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