Cabletron Systems 9032578-05 manual Limiting Traffic Rate, Rate Limiting Modes

Chapter 21: QoS Configuration Guide

Limiting Traffic Rate

Note: Some commands in this facility require updated SSR hardware. Please refer to Appendix A for details.

Rate limiting provides the ability to control the usage of a fundamental network resource, bandwidth. It allows you to limit the rate of traffic that flows through the specified interfaces, thus reserving bandwidth for critical applications. The SSR supports two modes of rate limiting; only one mode can be in effect at a time. The rate limiting modes are:

•Per-flow rate limiting mode allows you to configure policies that limit individual flows to a specified rate. This is the default rate limiting mode on the SSR.

•Aggregate rate limiting mode allows you to configure policies that limit an aggregation of flows (all flows that match an ACL) to a specified rate. For example, you can limit traffic to or from a particular subnet. Aggregate rate limiting mode also allows you to configure port-level rate limiting policies that limit traffic coming into a particular port. This type of policy can be used to limit any type of traffic.

For per-flow and aggregate rate limiting policies, a traffic profile is used to define the traffic characteristics before an upper limit is assigned. The traffic profile is created using an ACL, which can utilize any combination of the parameters supported in the IP ACL. A rate limiting policy can then be defined by using the ACL and traffic rate limitations. You define the action to be taken on the traffic that exceeds the upper limit; for example, drop the packets. Except for port rate limiting, the rate limiting policy is then applied to a logical IP interface.

Rate limiting policies work in only one direction; that is, only the traffic coming in on the interface to which a policy is applied will be subject to rate limiting (except for output port rate limiting policies, which are applied to egress ports). If both incoming and outgoing traffic to a network or subnet needs to be rate limited, then you should create separate policies to be applied to each interface.

Note: You can configure a maximum of 24 port and aggregate rate limiting policies per SSR line card.

Rate Limiting Modes

Per-flow rate limiting is enabled on the SSR by default. If you need to create aggregate or input port-level rate limiting policies, you must enable the aggregate rate limiting mode. If you enable aggregate rate limiting mode, you will not be able to configure new per-flow rate limiting policies.

The rate limiting mode can be changed only if there are no existing rate limiting policies. For example, before you can enable aggregate rate limiting mode, you need to delete any existing per-flow rate limiting policies.

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