For more information, see the documentation provided with the server application.
Option 82 server support
To apply DHCP Option 82, the routing switch must operate in conjunction with a server that supports Option 82.
(DHCP servers that do not support Option 82 typically ignore Option 82 fields.) Also, the routing switch applies
Option 82 functionality only to client request packets being
routed
to a DHCP server. DHCP relay with Option 82
does not apply to
switched
(non-routed) client requests.
For information on configuring policies on a server running DHCP Option 82, see the documentation provided for
that application.
Figure 49: Example of a DHCP Option 82 application
General DHCP Option 82 requirements and operation
Requirements
DHCP Option 82 operation is configured at the global config level and requires the following:
• IP routing enabled on the switch
• DHCP-relay option 82 enabled (global command level)
• Routing switch access to an Option 82 DHCP server on a different subnet than the clients requesting DHCP
Option 82 support
• One IP helper address configured on each VLAN supporting DHCP clients
General DHCP-relay operation with Option 82
Typically, the first (primary) Option 82 relay agent to receive a client's DHCP request packet appends an Option
82 field to the packet and forwards it toward the DHCP server identified by the IP helper address configured on
the VLAN in which the client packet was received. Other, upstream relay agents used to forward the packet may
append their own Option 82 fields, replace the Option 82 fields they find in the packet, forward the packet without
adding another field, or drop the packet. (Intermediate next-hop routing switches without Option 82 capability can
be used to forward—route—client request packets with Option 82 fields.) Response packets from an Option 82
server are routed back to the primary relay agent (routing switch) and include an IP addressing assignment for the
requesting client and an exact copy of the Option 82 data the server received with the client request. The relay
agent strips off the Option 82 data and forwards the response packet out the port indicated in the response as the
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