Juniper JUNOSE 11.1.X - BROADBAND ACCESS CONFIGURATION GUIDE 6-4-2010 Configuration Manual page 543

Chapter 20: Configuring DHCP Relay
To display whether the layer 2 unicast method is currently on or off on the router,
use the show dhcp relay command. For information, see "Monitoring and
Troubleshooting DHCP" on page 539.
The dhcpRelayGeneral logging event category uses the debug severity level to log
DHCP reply packets that are transmitted to clients using a layer 2 unicast address
and a layer 3 broadcast address.
The set dhcp relay broadcast-flag-replies command configures the router to use
the setting of the broadcast flag in DHCP request packets to control the transmission
of DHCP reply packets. The set dhcp relay layer2-unicast-replies command and
the set dhcp relay broadcast-flag-replies command are mutually exclusive. For
more information, see "Interaction with Layer 2 Unicast Transmission Method" on
page 499.
NOTE: When you enable the layer 2 unicast transmission feature, the DHCP relay
and DHCP relay proxy instance must be the next hop from the DHCP clients.
Otherwise, the DHCP reply packets might be discarded.
The layer 2 unicast transmission method is not supported on non-ASIC line modules.
To configure the optional broadcast transmission method:
host1(config)#set dhcp relay layer2-unicast-replies
Using Option 60 Strings to Forward Client Traffic to Specific DHCP Servers
The DHCP functionality supports the DHCP vendor class identifier option (option
60). This support allows DHCP relay to compare option 60 strings in received DHCP
client packets against strings that you configure on the router. You can use the DHCP
relay option 60 feature when providing converged services in your network
environment option 60 support enables DHCP relay to direct client traffic to the
specific DHCP server (the vendor-option server) that provides the service that the
client requires. Or, as another option, you can configure option 60 strings to direct
traffic to the DHCP local server in the current virtual router.
For example, you might have an environment in which some DHCP clients require
only Internet access, while other clients require IPTV service. The clients that need
Internet access get their addresses assigned by the DHCP local server on the E Series
router (in equal-access mode). Clients requiring IPTV must be relayed to a specific
DHCP server that provides the service. To support both types of clients, you configure
two option 60 strings on the DHCP relay. Now, when any DHCP client packets are
received with option 60 strings configured, the strings are matched against all strings
configured on the DHCP relay. If the client string matches the first string you
configured, that client is directed to the DHCP local server and gains Internet access.
Client traffic with an option 60 string that matches your second string is relayed to
the DHCP server that provides the IPTV service. In addition, you can configure a
default action, which DHCP relay performs when a client option 60 string does not
503
Configuring DHCP Relay and BOOTP Relay