DHCP relay class
support for client identification allows the Cisco relay agent to forward
client-generated DHCP messages to different DHCP servers based on the content
of the following four options:
vendor class identifier
vendor-identifying vendor class
vendor-identifying vendor-specific information
identifies the type of client that is sending the DHCP message.
provide a method to define DHCP pools that are not used for address allocation.
These relay pools can specify that DHCP messages from clients on a specific
subnet should be forwarded to a specific DHCP server. These relay pools can be
configured with relay classes inside the pool that help determine the
after receiving the option in a DHCP DISCOVER message, the relay agent will
match and identify the relay class from the relay pool and then direct the DHCP
DISCOVER message to the DHCP server associated with that identified relay
In an example
application, a Cisco device acting as a DHCP relay agent receives DHCP requests
from two VoIP services (H.323 and the Session Initiation Protocol [SIP]). The
requesting devices are identified by option 60.
services have a different back-office infrastructure, so they cannot be
serviced by the same DHCP server. Requests for H.323 devices must be forwarded
to the H.323 server, and requests from SIP devices must be forwarded to the SIP
server. The solution is to configure the relay agent with relay classes that
are configured to match option 60 values sent by the client devices. Based on
the option value, the relay agent will match and identify the relay class, and
forward the DHCP DISCOVER message to the DHCP server associated with the
identified relay class.
The Cisco IOS
DHCP server examines the relay classes that are applicable to a pool and then
uses the exact match class regardless of the configuration order. If the exact
match is not found, the DHCP server uses the first default match found.
3 through 5 for each DHCP class that you need to configure.
Steps 9 through 11 for each DHCP class that you need to configure.