Overview - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - BROADBAND ACCESS CONFIGURATION GUIDE 2010-10-12 Configuration Manual

Preservation of Dynamic Subscriber Interfaces with DHCP External Server Overview
Copyright © 2010, Juniper Networks, Inc.
Creates the subscriber's dynamic subscriber interface
If the SRC software is configured, the router also performs the following actions:
Alerts the SRC software that the dynamic subscriber interface exists
Alerts the SRC software that the subscriber's address exists and provides DHCP options
The SRC software then provides its enhanced services to the subscriber.
The E Series router monitors all traffic between the subscriber and the DHCP server, and
resets the shadow lease by monitoring the DHCP server/client lease renewal. When the
subscriber disconnects, the shadow lease will eventually expire. The E Series router then
performs the following actions:
Deletes the subscriber's dynamic subscriber interface
Alerts the SRC software that the dynamic subscriber interface has been deleted
Alerts the SRC software that the subscriber's address has been deleted
For additional information on managing client bindings, see "Viewing and Deleting DHCP
Client Bindings" on page 461.
You can configure the DHCP external server application to control whether the router
preserves or deletes and re-creates a DHCP client's existing dynamic subscriber interface
in certain situations.
The DHCP discovery process assigns an IP address to a DHCP client. A client initiates the
discovery process on a primary IP interface in the router. When this process completes
successfully, the IP subscriber manager application may create a dynamic subscriber
interface for the client that exists with the client's primary interface. A client normally
receives broadcast traffic, such as the traffic associated with the DHCP discovery process,
on its primary interface. A client normally receives unicast traffic, such as the traffic
associated with the DHCP renewal process, on its dynamic subscriber interface if one
exists.
A DHCP client that has successfully completed the discovery process and has been
assigned an IP address in the DHCP external server application is referred to as a bound
client. An IP address is leased to a client for a specified period of time. Before the lease
period expires, most bound DHCP clients typically use the DHCP renewal process to
extend their IP address lease. However, some bound DHCP clients might extend their IP
address lease by restarting the DHCP discovery process instead of using the DHCP renewal
process.
When a bound DHCP client on a dynamic subscriber interface extends its address lease
by restarting the discovery process on its primary IP interface, you can configure the DHCP
external server application to control whether the client's existing dynamic subscriber
interface is preserved, or deleted and re-created. By default, the DHCP external server
preserves the client's existing dynamic subscriber interface in this situation. To configure
the DHCP external server to delete and re-create the client's dynamic subscriber interface
Chapter 21: Configuring the DHCP External Server Application
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