Response packet
content
Option 82 configuration
Validation
enabled on the
relay agent
Validation
disabled (the
default)
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; see RFC 2131.)
Multinetted VLANs
On a multinetted VLAN, each interface can form an Option 82 policy boundary within that VLAN if the routing
switch is configured to use IP for the remote ID suboption. That is, if the routing switch is configured with IP as the
remote ID option and a DHCP client request packet is received on a multinetted VLAN, the IP address used in the
Option 82 field will identify the subnet on which the packet was received instead of the IP address for the VLAN.
This enables an Option 82 DHCP server to support more narrowly defined DHCP policy boundaries instead of
defining the boundaries at the VLAN or whole routing switch levels. If the MAC address option (the default) is
configured instead, the routing switch MAC address will be used regardless of which subnet was the source of the
client request. (The MAC address is the same for all VLANs configured on the routing switch.)
All request packets from DHCP clients in the different subnets in the VLAN must be able to reach any DHCP
server identified by the IP helper addresses configured on that VLAN.
308
Aruba 3810 / 5400R Multicast and Routing Guide for ArubaOS-
Switch 16.08