HP ProCurve 2610-PWR manual 294

IP Routing Features

Configuring DHCP Relay

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.

		Relay Agent “A”		Relay Agent “B”			Relay Agent “C”
Client		VLAN	VLAN	VLAN	VLAN		VLAN	VLAN		DHCP
			20		30			20
	10			20		10				Option
									82
		DROP		APPEND			APPEND			Server

Figure 7-15. 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”.

		Relay Agent “A”		Relay Agent “B”			Relay Agent “C”
Client		VLAN	VLAN	VLAN	VLAN		VLAN	VLAN		DHCP
			20		30			20
	10			20		10				Option
									82
		DROP		No Option 82			REPLACE			Server

Figure 7-16. 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 field(s) 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.

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