RADIUS-Sourced Weights for Interface and Interface Set Targeted Distribution
Targeted distribution is a way to load balance traffic between the member links of an aggregated Ethernet bundle by distributing the logical interfaces or interface sets across the links. Egress traffic for a subscriber is targeted for a single member link, making it possible to use a single CoS scheduler for the subscriber to optimize resource use.
Interfaces and interface sets are assigned to primary and backup member links to yield an even distribution of subscribers across all member links.
A link is selected as primary when it is up and has the lightest subscriber load. If no links are up then the available link with the lightest subscriber load is selected.
A link is selected as backup when it is the available link with the lightest subscriber load. The redundancy mode configured for the aggregated Ethernet bundle affects the pool of available links. For example, module redundancy excludes all links on the same module from being assigned as backup.
The subscriber load is also known as the link weight. You can configure an explicit weight for targeted subscribers based on factors important to you, such as CoS or bandwidth requirement. The member links are assigned based on the value of the weight. The weight is configured per dynamic profile for an interface or interface set. Starting in Junos OS Release 18.4R1, you can have RADIUS supply the weight value per subscriber. To do so, specify either of the following predefined variables that corresponds to the relevant RADIUS VSA conveyed in the Access-Accept message when a subscriber is authenticated.
$junos-interface-target-weight corresponds to VSA 26-214, Interface-Targeting-Weight.
$junos-interface-set-target-weight corresponds to VSA 26-213, Interface-Set-Targeting-Weight.
Diameter AVPs 213 and 214 can be used for the same purpose during NASREQ processing.
When you use a dynamic interface set with targeted distribution, the interface set and its member interfaces are assigned to the same aggregated Ethernet member link. This means that you have to configure targeted distribution for both the interface set and its member interfaces. The dynamic interface set is created when the first member interface is instantiated. The weight that is used to associate the interface set and its members to the aggregated Ethernet member link is either of the following:
The weight assigned to the interface set. The interface set weight is either explicitly configured or sourced from RADIUS VSA 26-214 when the first member interface is authorized.
The weight assigned to the first member interface. The interface weight is used when the interface set has no assigned weight. The weight for the first member interface is either explicitly configured or sourced from RADIUS VSA 26-213 when the first member interface is authorized.
Always ensure that a weight is assigned to the interface set by the CLI configuration or by RADIUS.
Because the weight of the first instantiated member interface can provide the weight for the interface set, the weights of subsequent member interfaces have no effect on the assignment of the interface set and its members to a given aggregated Ethernet member link.
We recommend that the weight assigned to the interface set be representative of the member interfaces to ensure optimal distribution among the aggregated Ethernet member links. Consequently, there is no advantage to sourcing weights from RADIUS for both the interface set and its member interfaces, because sourcing the weight for only the interface set is sufficient.
The RADIUS-sourced weight for an interface set cannot change after the set is created when the first member interface is authorized. Consequently, only interfaces having the same weight as the first interface can become members of the interface set. Consider the following example:
Suppose that when the first dynamic subscriber interface is authorized, the authorization from RADIUS includes VSA 26-214 with a value of 100.
The interface set is then assigned a weight of 100 based on the first interface weight.
When the second dynamic subscriber interface is authorized, the authorization includes VSA 26-214 with a value of 200.
Because the weight for the interface set cannot change; it remains at 100 and the instantiation of the subscriber session on the second interface fails.
Benefits of RADIUS-Sourced Weighting
Enables per-subscriber weighting based on RADIUS user record, rather than per dynamic profile.