Dynamic Bandwidth Allocation Among Traffic Flows in SRC Policy Lists for JunosE Routing Platforms

Rate-Limit Hierarchies Overview

SRC support for JunosE rate-limit hierarchies lets you configure hierarchical policies to dynamically share unused bandwidth from high-priority traffic with lower priority traffic. A rate-limit hierarchy is a defined series of rate limits that a packet traverses within a policy list. At each level in the hierarchy, the packet is evaluated and processed as configured. Traffic preferences set in a hierarchy can specify the bandwidth allocated to a combined traffic flow and to several traffic flows within the combined flow. For example, a traffic flow may include video traffic and Internet traffic. The video traffic would have a high priority, but during times when not all bandwidth allocated to video is in use, the Internet traffic can access the unused bandwidth.

Rate-limit hierarchies also enable real-time traffic to use all guaranteed bandwidth below a configured maximum. Traffic is transmitted depending on the rate limit set for the traffic flow. Preferred, high-priority traffic packets are dropped only as configured by the rate limit for that traffic flow. Lower priority traffic, however, can be dropped to keep the total traffic flow below a configured maximum limit.

Internal Parent Groups in Rate-Limit Hierarchies

An internal parent group is an object that defines a rate-limit action. An internal parent group can contain other parent groups or be subordinate to another parent group to form a hierarchy. When you configure rate-limit hierarchies, you configure internal parent groups (in a policy list) that specify the rate-limit configurations and configure traffic match conditions, which reference the parent groups.

You can configure a maximum of three hierarchy levels under a parent group. SRC parent groups support input, secondary-input, and output lists and can be configured for lists that have roles for JunosE IPv4 and JunosE IPv6.

An internal parent group must contain another parent group or be referenced by a policy rule. The rate limit configured for an internal parent group must be configured to support hierarchical rate limits. It can also be configured to be color-aware, that is to detect ToS byte marking for red, yellow, and green. If the rate limit is color aware, a rate limit in the hierarchy can change the color of the incoming packet. An incoming packet may have the color already set by a previous rate limit or by a previous policy, such as an inbound IP or VLAN policy. Mark actions in the entire hierarchy can change the ToS values depending on the color of the packet. If the rate limit is not color aware, all packets are processed in the same way.

External Parent Groups

The SRC software supports aggregate rate-limiting for JunosE dual-stack subscribers (IPv4 and IPv6). Traffic flow can be rate-limited by a common external rate-limit profile. This is accomplished by defining higher-level external parent group rate-limit profiles and hierarchical policy parameters, which can be applied to lower-level classifier flows. External parent groups are defined externally to a policy list, so you can reference them in any policy you define in the SRC software.

Actions in Rate-Limit Hierarchies

You configure the action to be taken on traffic as packets traverse a rate-limit hierarchy. At each level in a rate-limit hierarchy, traffic may:

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