IP Routing Features
Configuring DHCP Relay
Syntax
:
dhcp-relay option 82 < append [validate] | replace [validate] | drop [validate] | keep >
[ip | mac | mgmt-vlan]
— Continued —
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 use the incoming VLAN’s
IP address or the Management VLAN IP address (if configured) for the
remote ID instead of the switch MAC address, use the
ip
or
mgmt-vlan
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 3-56
.
[ ip | mac | mgmt-vlan ]
This option specifies the remote ID suboption that the switch uses in Option
82 fields added or appended to DHCP client packets. The type of remote ID
defines DHCP policy areas in the client requests sent to the DHCP server. If
a remote ID suboption is not configured, then the routing switch defaults to
the
mac
option. (Refer to “Option 82 Field Content” on page 3-52.)
ip:
Specifies the IP address of the VLAN on which the client DHCP packet enters
the switch.
mac:
Specifies the routing switch’s MAC address. (The MAC address used is
the same MAC address that is assigned to all VLANs configured on the
routing switch.) This is the default setting.
mgmt-vlan:
Specifies the IP address of the (optional) Management VLAN
configured on the routing switch. Requires that a Management VLAN is
already configured on the switch. If the Management VLAN is multi-
netted, then the primary IP address configured for the Management VLAN
is used for the remote ID.
If you enter the
dhcp-relay option 82
command without specifying either
ip
or
mac
, the MAC address of the switch on which the packet was received from
the client is configured as the remote ID. For information about the Remote
ID values used in the Option 82 field appended to client requests, see “Option
82 Field Content” on page 3-52.
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