Use Juniper BNG CUPS Subscriber Groups

Subscriber Groups Overview

The TR 459 Multi-Service Disaggregated BNG with CUPS. Reference Architecture, Deployment Models, Interface, and Protocol (TR-459) specification explains how the disaggregation of the BNG improves subscriber resilience. This is due to the fact that the disaggregated control plane (in this case, the BNG CUPS Controller), contains a centralized master state database for all of the disaggregated user planes (BNG User Planes) under its control. Figure 1 (from TR-459) shows how the BNG User Planes provide resilience across the BNG User Planes where the BNG Cups Controller holds the master state for any subscriber session. The BNG User plane then holds active forwarding state, or backup forwarding state for a particular subscriber session.

Subscriber sessions that are subject to the same restoration capability are placed into the same subscriber group. Grouping subscribers together helps to increase core routing efficiency.

The use of subscriber groups minimizes the messaging, which reduces the elapsed time between the detection of a failure (or any request to switchover from active to backup) and the restoration of the service.

The active or backup state is set at the subscriber group level and communicated to the relevant BNG User Plane by the BNG CUPS Controller. Subscriber sessions are tagged with the subscriber group to which they belong when the session is established. All resiliency actions are communicated at the subscriber group level rather than at the session level.

Subscriber groups are created based on the BNG User Plane interfaces.

Resilient subscriber groups have the following characteristics:

• Spans at least two BNG User Planes.
• Contains one or more redundancy interfaces. Redundancy interfaces consist of one interface on each BNG User Plane.
• Is active, only on one BNG User Plane at a time. Subscribers are only serviced by the subscriber's active BNG User Plane. Also, all interfaces in the subscriber group move at the same time.
• BNG User Planes can have more than one subscriber group associated to them.

Subscriber address management operates with subscriber groups in the following ways:

• Subscriber IP addresses must come from its subscriber group's defined address domains (made up of prefixes). Domains are created dynamically based upon, the RADIUS VSA, SGRP name and routing instance.
• Address prefixes are advertised differently on active and backup BNG User Planes.

Subscriber management switchover consists of the following:

• Switchover can be controlled by either the BNG CUPS Controller or the BNG User Planes.
• Route advertisement metrics are changed during subscriber group switchover.

The address domain prefixes and their associated metrics allow policies to be applied per BNG User Plane. This is so that the routing policy fits within any local variations, and the preferred metric can be applied upon subscriber group switchover.

You configure a subscriber group on the BNG CUPS Controller with the following settings:

• A subscriber group name and a subscriber group identifier (a unique 32bit unsigned integer)
• State—Active, backup, or Track-Logical-Port
• Active BNG User Plane and backup BNG User Plane
• Logical ports, and virtual MAC address
• Prefixes and tags

In the BNG CUPS Controller, the subscriber group is configured with details about the BNG User Planes and the list of logical ports for each of the BNG User Planes. In a BNG CUPS Controller managed subscriber group, the BNG CUPS Controller sends subscriber group notifications to the BNG User Planes with either, an active or backup state and the respective port list.

In a resilient subscriber group, when the subscriber logs into the subscriber session, services are simultaneously created at both of the BNG User Planes. The services are also tagged with the subscriber group ID. At this time, the subscriber sessions associated with the backup BNG User Plane discards all packets in both directions.

There are two types of subscriber groups, either a BNG CUPS Controller managed subscriber group or a BNG User Plane managed subscriber group.

A BNG User Plane managed subscriber group is a resilient subscriber group with a single logical port pair and its state set to Track-Logical-Port (TLP). A TLP or BNG User Plane managed subscriber group (also referred to as subscriber group type TLP) requires that the BNG CUPS Controller set the subscriber group state to Track-Logical-Port on both the active and backup BNG User Plane instances. This specifies the logical ports for which the BNG User Planes track the state. The BNG User Plane tracks the operational state of the access network's connectivity on the logical ports. This determines if and when the switchover occurs. The two BNG User Planes that belong to a BNG User Plane managed subscriber group are assumed to be linked by an active to backup connection on the access side. The two BNG User Planes decide, by themselves, which one of the two handles the sessions. This decision is made based on their relevant logical ports.

The following example shows the configuration of a BNG User Plane managed subscriber group on a BNG CUPS Controller:

A BNG CUPS Controller managed subscriber group is a resilient subscriber group with one or more logical port pairs, where the BNG CUPS Controller only programs active and backup states on the BNG User Planes (also known as subscriber group Type A/B). As a best practice, the BNG CUPS Controller subscriber group should be configured with a single redundancy interface (or a single port pair).

The following example shows the configuration of a BNG CUPS Controller subscriber group:

Hot backup support ensures that upon switchover, subscriber activity and traffic is unaffected with little or no packet loss.

To check the state of the subscriber group on the BNG CUPS Controller, you can run the show subscriber-group command:

Switchover triggers the use of the subscriber group. Switchover can be split into a BNG CUPS Controller initiated switchover or a BNG User Plane initiated switchover.

You use the request subscriber-group switchover command to initiate a BNG CUPS Controller initiated switchover.

After the BNG CUPS Controller initiated switchover, the BNG User Plane jersey is no longer the active BNG User plane, but is now the backup BNG User Plane. See the following show subscriber-group command output:

Default Subscriber Groups

A default subscriber group is the subscriber group that is automatically created when a BNG User Plane is associated with the BNG CUPS Controller. If there are no additional BNG User Planes assigned to the default subscriber group, the subscriber group is not resilient.

In the hitless (meaning, subscriber activity and traffic is unaffected with little or no packet loss) maintenance use case, a backup BNG User Plane gets automatically added to the default subscriber group for the BNG User Plane that is being serviced. This action preserves the existing subscriber traffic and state while maintenance is performed on the BNG User Plane. When the maintenance is completed, the backup BNG User Plane is removed from the default subscriber group of the serviced BNG User Plane.

Additional Subscriber Group Information

Each subscriber group has its own address prefixes that do not overlap with other subscriber group's address prefixes.

When a subscriber logs out or a subscriber cleanup is triggered by deleting a subscriber group, the BNG CUPS Controller collects the final statistics from both the backup and active BNG User Planes.

For BNG User Plane managed subscriber group, active and backup pseudowire or EVPN can be used in the Access Network.

BNG CUPS Controller managed switchover and BNG User Plane managed switchover might be mutually exclusive depending on the Access Network technology.

In the hitless maintenance user case, there should be little or no disruption to a subscriber’s activity and network traffic should remain uninterrupted while the BNG User Plane is serviced. Hitless maintenance is one of the use cases that uses the BNG CUPS Controller managed subscriber group and the BNG CUPS Controller initiated switchover.

To perform maintenance operations using configured subscriber groups (subscribers and services are already installed in on the subscriber group's backup BNG User Planes) you use BNG CUPS Controller initiated switchover to seamlessly move traffic to the backup BNG User Planes for the subscriber groups that contain the BNG User Plane that is under maintenance.

When maintenance is completed, you then perform a BNG CUPS Controller initiated switchover again and the BNG User Plane that was serviced becomes the active BNG User Plane for the subscriber groups.

There are many switchover triggers that change the active state for a particular subscriber group from one BNG User Plane to a different BNG User Plane:

• Operator driven trigger through the management interface of the BNG CUPS Controller.
• Failure of an entire BNG User Plane.
• Failure of a component of the BNG User Plane that impacts a set of active subscriber sessions.
• The failure of a link or interface directly connected to the BNG User Plane that impacts a logical port and active subscriber sessions.
• A change in the negotiated status of a resilient connection between the BNG User Plane and the Aggregation Network
• A change in the IP core network that isolates a BNG User Plane from the rest of the network.