Servers - Juniper JUNOSE SOFTWARE 11.2.X - BROADBAND ACCESS CONFIGURATION GUIDE 7-20-2010 Configuration Manual

Using Option 60 Strings to Forward Client Traffic to Specific DHCP Servers
Copyright © 2010, Juniper Networks, Inc.
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 487.
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
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 match any strings you have configured—for example,
you might specify that all clients with non-matching strings be dropped.
You use the set dhcp vendor-option command to configure vendor-option (option 60)
strings to control DHCP client traffic Create DHCP vendor-option servers by configuring
Chapter 20: Configuring DHCP Relay
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