IP Routing Features
Configuring DHCP Relay
Note The routing switch’s DHCP Relay Information (Option 82) feature can be used
in networks where the DHCP server(s) are compliant with RFC 3046 Option
82 operation. DHCP Servers that are not compliant with Option 82 operation
ignore Option 82 fields. For information on configuring an Option 82 DHCP
server, refer to the documentation provided with the server application.
Some client applications can append an Option 82 field to their DHCP
requests. Refer to the documentation provided for your client application.
It is not necessary for all relay agents on the path between a DHCP client and
the server to support Option 82, and a relay agent without Option 82 should
forward DHCP packets regardless of whether they include Option 82 fields.
However, Option 82 relay agents should be positioned at the DHCP policy
boundaries in a network to provide maximum support and security for the IP
addressing policies configured in the server.
Option 82 Server Support
To apply DHCP Option 82, the routing switch must operate in conjunction with
a server that supports Option 82. (DHCP servers that do not support Option
82 typically ignore Option 82 fields.) Also, the routing switch applies Option
82 functionality only to client request packets being routed to a DHCP server.
DHCP relay with Option 82 does not apply to switched (non-routed) client
requests.
For information on configuring policies on a server running DHCP Option 82,
refer to the documentation provided for that application.
Switch “A”
10.10.10.2
VLAN
10
10.10.10.1
Client
3
DHCP
Option
82
Server
Subnets 10 and 20 in relay agent “1”
form policy boundaries that can be
defined by the IP address of the subnet
on which the client request is received.
Relay Agent “1” (Routing Switch)
with DHCP Option 82 Enabled
Client
1
Client
2
VLAN
20
10.10.20.1
Switch “B”
10.10.20.3
Client
6
Client
4
Client
5
10.10.20.2
10.10.30.1
Relay Agent “2” (Routing
Switch) without DHCP
Option 82 Enabled
Policy Boundaries
Figure 3-19. Example of a DHCP Option 82 Application
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