Configuring The Dhcp External Server To Support The Creation Of Dynamic Subscriber Interfaces - Juniper JUNOSE 11.1.X - BROADBAND ACCESS CONFIGURATION GUIDE 6-4-2010 Configuration Manual

JUNOSe 11.1.x Broadband Access Configuration Guide
The dropped traffic situation can occur because of the way some DSLAMs create the
giaddr that is sent to the DHCP external server application. Some Ethernet DSLAMs
use a DHCP relay implementation that inserts giaddr values and relay agent options
in DHCP packets that are received from end users. The intent is that this information
is provided to a DHCP server, which uses the values to determine the configuration
parameters for the subscriber.
However, when the DHCP external server application receives the giaddr from an
Ethernet DSLAM, the application installs the subscriber access route with the Ethernet
DSLAM's IP address as the next hop, This operation results in the subscriber-destined
traffic being incorrectly sent to the Ethernet DSLAM, which cannot process the traffic.
To avoid dropping the traffic in this situation, use the ip set dhcp-external
disregard-giaddr-next-hop command to configure the DHCP external server
application to ignore the giaddr when determining the next hop for the subscriber
access routes. The E Series router then uses Address Resolution Protocol (ARP) to
discover the subscriber's IP address and sends the traffic to the learned IP address.
To configure the DHCP external server application to ignore the giaddr when
determining the next hop for the subscriber access routes:
Related Topics
Configuring the DHCP External Server to Support the Creation of Dynamic
Subscriber Interfaces
You can configure the DHCP external server to support the creation of dynamic
subscriber interfaces. This configuration requires that the user's DHCP control traffic
and data traffic traverse the same client-facing ingress port on the E Series router.
You must use the ip dhcp-external auto-configure command within a specific virtual
router context.
To configure the DHCP external server to support the creation of dynamic subscriber
interfaces:
To configure the DHCP external server to support the creation of dynamic subscriber
interfaces built over dynamic VLANs that are based on the agent-circuit-id option
(suboption 1) of the option 82 field in DHCP messages, include the
agent-circuit-identifier keyword.
530

Configuring the DHCP External Server to Support the Creation of Dynamic Subscriber Interfaces

Issue the ip dhcp-external disregard-giaddr-next-hop command from Global
Configuration mode:
host1(config)#ip dhcp-external disregard-giaddr-next-hop
ip dhcp-external disregard-giaddr-next-hop
Issue the ip dhcp-external auto-configure command from Global Configuration
mode:
host1(config)#ip dhcp-external auto-configure