Product guide

IP Routing Features
Configuring DHCP Relay
Configuring Option 82 Operation on the Routing Switch
Syntax: dhcp-relay option 82 < append [validate] | replace [validate] | drop [validate] | keep > [ip | mac]
append: Configures the routing switch to append an Option 82 field to the
client DHCP packet. If the client packet has any existing Option 82
field(s) assigned by another device, then the new field is appended to the
existing field(s).
The appended Option 82 field includes the switch Circuit ID (inbound
port number*) associated with the client DHCP packet, and the switch
Remote ID. The default switch remote ID is the MAC address of the switch
on which the packet was received from the client. To use the incoming
VLAN’s IP address instead of the switch MAC address for the remote ID,
use the ip option (below).
replace: Configures the routing switch to replace any existing Option 82
field(s) in an inbound client DHCP packet with one Option 82 field for
the current routing switch.
The replacement Option 82 field includes the switch circuit ID (inbound
port number*) associated with the client DHCP packet, and the switch
remote ID. The default switch remote ID is the MAC address of the switch
on which the packet was received from the client. To use the incoming
VLAN’s IP address instead of the switch MAC address for the remote ID,
use the ip option (below).
drop: Configures the routing switch to unconditionally drop any client DHCP
packet received with existing Option 82 field(s). This means that such
packets will not be forwarded. Use this option where access to the routing
switch by untrusted clients is possible.
If the routing switch receives a client DHCP packet without an Option 82
field, it adds an Option 82 field to the client and forwards the packet. The
added Option 82 field includes the switch circuit ID (inbound port
number*) associated with the client DHCP packet, and the switch remote
ID. The default switch remote ID is the MAC address of the switch on
which the packet was received from the client. To u s e th e i n co m in g VL A N ’s
IP address instead of the switch MAC address for the remote ID, use the
IP option (below).
keep: For any client DHCP packet received with existing Option 82 field(s),
configures the routing switch to forward the packet as-is, without
replacing or adding to the existing Option 82 field(s).
[ validate ]: This option operates when the routing switch is configured with
append, replace, or drop as a forwarding policy. With validate enabled,
the routing switch applies stricter rules to an incoming Option 82 server
response to determine whether to forward or drop the response. For more
information, refer to “Validation of Server Response Packets” on page 3-33.
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