Multiple Option 82 Relay Agents In A Client Request Path; Validation Of Server Response Packets - HP 2920 Series Multicast And Routing Manual

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 7 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 next two relay agent hops ("B" and "C".) The server can then
enforce an IP addressing policy based on the Option 82 field generated by the edge relay agent
("A".) In this example, the DHCP policy boundary is at relay agent 1.
Figure 8 Example configured to allow multiple relay agents to contribute an Option 82 field
This is an enhancement of the previous example. In this case, each hop for an accepted client
request adds a new Option 82 field to the request. A DHCP server capable of using multiple Option
82 fields can be configured to use this approach to keep a more detailed control over leased IP
addresses. In this example, the primary DHCP policy boundary is at relay agent "A," but more
global policy boundaries can exist at relay agents "B" and "C."
Figure 9 Example allowing only an upstream relay agent to contribute an Option 82 field
Like the first example, above, this configuration drops client requests with spurious Option 82 fields
from clients on the edge relay agent. However, in this case, only the Option 82 field from the last
relay agent is retained for use by the DHCP server. In this case the DHCP policy boundary is at
relay agent "C." In the previous two examples the boundary was with relay "A."

Validation of server response packets

A valid Option 82 server response to a client request packet includes a copy of the Option 82
fields the server received with the request. With validation disabled, most variations of Option 82
information are allowed, and the corresponding server response packets are forwarded.
Configuring DHCP relay 71