Overview of Processing IPCP Negotiations for Dual-Stack Subscribers

In a dual-stack network topology, which contains both IPv4 and IPv6 subscriber sessions, either as independent or combined sessions, you can enable the PPP application running on the router to send a message to the AAA server immediately after an IPv4 address is released by a client. The PPP link between the customer premises edge equipment (CPE) and the provider edge (PE) devices can be configured for both IPv4 and IPv6 protocols for transmission of data. The PPP application uses Link Control Protocol (LCP) negotiations to establish the connection with the subscriber.

After the PPP application authenticates the subscriber or CPE using the configured authentication protocol, the AAA server sends both IPv4 and IPv6 addresses in dual-stack networks to the PPP application. These addresses can be assigned from either the local address pool or the AAA server, which can be a server configured for RADIUS authentication. PPP enables the creation of a dynamic IPv4 or IPv6 interface, or both these types of interfaces based on the user environment. A dynamic interface is created, after the receipt of incoming requests from the subscriber or the CPE. The dynamic IPv4 or IPv6 interface created and stacked over the underlying physical PPP interface obtains its settings from the attached interface profile and the subscriber details returned by the AAA or RADIUS server. After a link has been established and optional facilities have been negotiated as needed by the LCP, PPP sends Network Control Protocol (NCP) packets.

When the CPE sends Internet Protocol Control Protocol (IPCP) messages during the NCP negotiation process, the AAA server sends IPv4 or IPv6 addresses to the CPE. Based on a successful negotiation, PPP notifies the IP application that the IP service is activated. The IP application installs an access route for the relevant IP address of the client to transmit data packets to it. When a dual-stack subscriber terminates the IPCP negotiation for only the IPv4 address, the IPv4 address is released to the PPP application. You can enable PPP to send a message to the AAA server immediately after the address is freed up by the client. This immediate, periodic notification enables optimal, effective usage of IPv4 addresses from the AAA server. This behavior is applicable only if the IPv4 address is allocated previously from the AAA server and not from the local address pool or the DHCP local server.

In such a scenario, the IPv6 address client of the dual-stack user is retained with the user. The released IPv4 address cannot be renegotiated. The client must send a new IPCP configuration request to obtain a fresh IPv4 address.

Guidelines for Configuring the AAA Server for Release of IPv4 Addresses for Dual-Stack Subscribers

Keep the following points in mind when you enable PPP to send a notification to the AAA server to release IPv4 addresses of dual-stack subscriber sessions for terminated IPv4 connections:

Communicating to the AAA server about released IPv4 addresses is not effective in the following situations:

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