Enterasys Networks 2H252, 2E253, 2H253, 2H258 manual More About Rate Limiting, Example

Rate Limiting Configuration Screen

8.8.3More About Rate Limiting

Rate Limiting enables Service Providers in Multi-Dwelling-Unit (MDU) and similar environments to offer varied bandwidth to customers using low cost Ethernet connections. Another solution for the enterprise, is to provide high priority bandwidth on the network for guaranteed service level agreements.

NOTE: When allocating the maximum rate per port, the maximum bandwidth of the uplink must be kept in mind. For example, if the ports are all set to 10 Mbps and there are 24 ports, this equals 240 Mbps of bandwidth. If the uplink is only 100 Mbps, there is an obvious problem if the network administrator guaranteed more bandwidth than the uplink can support.

In Multi-Dwelling Unit (MDU) or similar environments, the Rate Limiting feature can be activated per port to adjust the usable bandwidth on a 10 Mbps Ethernet or other type of physical connection. In residential housing, the service provider may offer multiple internet service packages, each offering different bandwidth at a different price. These offerings can be supported using low cost 10 Mbps Ethernet ports wired to each dwelling.

In the enterprise network, this feature (combined with Layer 3/4 prioritization) can provide guaranteed delivery of high priority traffic through a congested network fabric. This is accomplished through the construction of a committed information rate (CIR) fabric within the traditional best effort enterprise LAN fabric.

Example

This is a simple example intended to show how the Rate Limiting feature can be applied to solve a problem.

Assume that a network was built using SmartSwitch 6000 chassis in each wiring closet and interconnected with SmartSwitch Routers using Gigabit Ethernet links. Also, assume that 100 users are attached to each SmartSwitch 6000 chassis through 100 Mbps Ethernet ports. If each user attempted to transfer data out of the wiring closet at the maximum possible rate, there could be up to 10 Gbps (100 users x 100 Mbps) of traffic attempting to leave the chassis over a single gigabit link. In this situation, much of the traffic will be arbitrarily dropped.

Now assume that the system administrator wants to guarantee the delivery of SAP R/3 traffic by prioritizing it above all other incoming traffic to the chassis. (Unless the inbound rate of the SAP traffic can be controlled, the guarantee still cannot be made because of the potential for oversubscription of the inbound gigabit link by high priority traffic.)

8-44802.1p Configuration Menu Screens