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Page 17 | AlliedWare™ OS How To Note: DHCP Snooping on Rapier-style switches
Configuration examples
Configuring the switch for DHCP snooping, filtering,
and Option 82, when it is acting as a layer 3 BOOTP
Relay Agent
In a layer 3 routing environment, the switch takes on a role of BOOTP Relay Agent, with
support for DHCP Option 82. The relay agent inserts the information mentioned above
when forwarding client-originated DHCP packets to a DHCP server. DHCP servers that are
configured to recognise the relay agent information option may use the information to keep a
log of switches and port numbers that IP addresses have been allocated to, and may also use
this information for various address assignment policies.
The DHCP server echoes the option back to the relay agent in server-to-client replies, and
the relay agent strips the option before forwarding the reply to the client (RFC 3046). This
process is shown in the following figure.
create vlan="Customers" vid=48
create vlan="Network" vid=50
Here the DHCP Server is on VLAN 50, while the DHCP clients are on VLAN 48.
add vlan="48" port=1-24
add vlan="50" port=25
X Configure two VLANs for layer 3 access to the DHCP server:
X Add ports to the VLANs:
(1). DHCP client sends request.
(2). Relay agent appends
Option 82 to client sourced
packets.
(4). Relay agent strips
Option 82, and forwards
to client.
(3). Option 82 enabled DHCP
server allocates address
and stores the
to the relay agent.
Option 82 information.
Option 82 echoed
Server sends offer, with