Option 82
configuration
DHCP client request packet inbound to the routing switch
Packet has
no Option 82
field
Packet includes an Option 82 field
Replace
Append an
Option 82 field
Replace
replaces any existing Option 82 fields from downstream relay agents (and/or
the originating client) with an Option 82 field for the current relay agent.
Some applications for
replace
include:
• The relay agent is located at a point in the network that is a DHCP policy
boundary, and you want to replace any Option 82 fields appended by
down-stream devices with an Option 82 field from the relay agent at the
boundary. (This eliminates downstream Option 82 fields you do not want
the server to use when determining which IP addressing policy to apply to
a client request.)
• In applications where the routing switch is the primary relay agent for
clients that may append their own Option 82 field, you can use
replace
to delete these fields if you do not want them included in client requests
reaching the server.
Drop
Append an
Option 82 field
Drop
causes the routing switch to drop an inbound client request with an Option
82 field already appended. If no Option 82 fields are present,
drop
causes
the routing switch to add an Option 82 field and forward the request. As a
general guideline, configure
drop
on relay agents at the edge of a network,
where an inbound client request with an appended Option 82 field may be
unauthorized, a security risk, or for some other reason, should not be
allowed.
Multiple Option 82 relay agents in a client request path
Where the client is one router hop away from the DHCP server, only the Option 82 field from the first (and only)
relay agent is used to determine the policy boundary for the server response. Where there are multiple Option 82
router hops between the client and the server, you can use different configuration options on different relay agents
to achieve the results you want. This includes configuring the relay agents so that the client request arrives at the
server with either one Option 82 field or multiple fields. (Using multiple Option 82 fields assumes that the server
supports multiple fields and is configured to assign IP addressing policies based on the content of multiple fields.)
Figure 51: Example configured to allow only the primary relay agent to contribute an Option 82 field
The above combination allows for detection and dropping of client requests with spurious Option 82 fields. If none
are found, the drop policy on the first relay agent adds an Option 82 field, which is then kept unchanged over the
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