VIMCOM ES-2226C, Руководство пользователя

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ES-2226C User Manual
Publication date: Aug., 2008
Revision A4
43
3-1-7. DHCP Option 82
DHCP relay agent information option
－
Configuring the DHCP Option 82
Function name:
DHCP Option 82
Function description:
This feature enables the Dynamic Host Configuration Protocol (DHCP) relay
agent information (option 82) (ES-2226C switch) to include information about
itself and the attached client when forwarding DHCP requests from a DHCP
client to a DHCP server via Trust Port. The DHCP server can use this
information to assign IP addresses
、
gateway
、
subnet mask
、
DNS for each
subscriber of a service-provider network.
The host (DHCP client) generates a DHCP request and broadcasts it on the
network.
The switch (DHCP relay agent) intercepts the broadcast DHCP request packet
and inserts the relay agent information option (option 82) in the packet. The
relay information option contains the switch's MAC address (the remote ID
suboption) and the port from which the packet is received (circuit ID suboption).
The switch forwards the DHCP request that includes the option-82 field to the
DHCP server.
The DHCP server receives the packet. If the server is option-82 capable, it
might use the remote ID, the circuit ID, or both to assign IP addresses and
implement policies, such as restricting the number of IP addresses that can be
assigned to a single remote ID or circuit ID. Then the DHCP server echoes the
option-82 field in the DHCP reply.
If the server does not support option 82, it ignores the option and does not
echo it in the reply.
Fig. 3-10