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Page 14 | AlliedWare™ OS How To Note: DHCP Snooping on Rapier-style switches
Configuration examples
Configuration examples
This section contains the following examples:
z "Configuring the switch for DHCP snooping, filtering and Option 82, when it is
acting as a layer 2 switch" on page 14
z "Configuring the switch for DHCP snooping, filtering, and Option 82, when it is
acting as a layer 3 BOOTP Relay Agent" on page 17
Configuring the switch for DHCP snooping, filtering and
Option 82, when it is acting as a layer 2 switch
In a layer 2 switching environment, a switch configured with Option 82 snooping will snoop
any client-originated DHCP packets and insert Option 82 information into it before
forwarding the packet(s) to the DHCP server. In this sense it is a layer 2 relay agent; the
packet source and destination addresses are not altered.
DHCP servers that are configured to recognise the relay agent information option (Option
82) may use the information to keep a log of switches and port numbers that IP addresses
have been allocated to, and may also use the information for various address assignment
policies.
The DHCP server echoes the option back verbatim to the relay agent in server-to-client
replies, and the relay agent strips the option before forwarding the reply to the client. This
process is shown in the following figure.
create vlan="Customers" vid=48 private
A private VLAN provides security so customers will not be able to directly connect to or
detect each other.
X Configure a private VLAN for customers:
(1). DHCP Client sends request
(2). Layer 2 Relay Agent appends
Option 82 to client sourced
packets
(4). Layer 2 Relay Agent strips
Option 82 from the offer packet
to client
(3). Option 82 enabled DHCP
to the layer 2 relay agent
Option 82 information
Option 82 echoed
Server sends offer, with
server allocates address
and stores the
and forwards