HP 2610-PWR - Manual (Page 295)

IP Routing Features
Configuring DHCP Relay
Server response validation is an option you can specify when configuring
Option 82 DHCP for
append, replace, or drop operation. (Refer to “Forwarding
Policies” on page 7-34.) Enabling validation on the routing switch can enhance
protection against DHCP server responses that are either from untrusted
sources or are carrying invalid Option 82 information.
With validation enabled, the relay agent applies stricter rules to variations in
the Option 82 field(s) of incoming server responses to determine whether to
forward the response to a downstream device or to drop the response due to
invalid (or missing) Option 82 information. Table <zBlue>7-4, below, illus­
trates relay agent management of DHCP server responses with optional
validation enabled and disabled.
Table 7-4. Relay Agent Management of DHCP Server Response Packets
Response Packet Content Option 82
Configuration Validation Enabled on the Relay
Agent Validation Disabled (The
Default)
Valid DHCP server response
packet without an Option 82
field. append, replace,
or drop
1
Drop the server response
packet. Forward server response
packet to a downstream device.
keep
2
Forward server response
packet to a downstream device. Forward server response
packet to a downstream device.
The server response packet
carries data indicating a given
routing switch is the primary relay
agent for the original client
request, but the associated
Option 82 field in the response
contains a Remote ID and Circuit
ID combination that did not origi­
nate with the given relay agent. append Drop the server response
packet. Forward server response
packet to a downstream device.
replace or drop
1
Drop the server response
packet. Drop the server response
packet.
keep
2
Forward server response
packet to a downstream device. Forward server response
packet to a downstream device.
The server response packet
carries data indicating a given
routing switch is the primary relay
agent for the original client
request, but the associated
Option 82 field in the response
contains a Remote ID that did not
originate with the relay agent. append Drop the server response
packet. Forward server response
packet to a downstream device.
replace or drop
1
Drop the server response
packet. Drop the server response
packet.
keep
2
Forward server response
packet to a downstream device. Forward server response
packet to a downstream device.
All other server response
packets
3
append, keep
2
,
replace, or drop
1
Forward server response
packet to a downstream device. Forward server response
packet to a downstream device.
1
Drop is the recommended choice because it protects against an unauthorized client inserting its own Option 82 field for
an incoming request.
2
A routing switch with DHCP Option 82 enabled with the keep option forwards all DHCP server response packets except
those that are not valid for either Option 82 DHCP operation (compliant with RFC 3046) or DHCP operation without Option
82 support (compliant with RFC 2131).
3
A routing switch with DHCP Option 82 enabled drops an inbound server response packet if the packet does not have
any device identified as the primary relay agent (giaddr = null; refer to RFC 2131).
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