4. Port-Level Egress Rate Limiting

This chapter provides information to configure the port-level egress-rate command using the CLI.

4.1. Overview

Egress port rate limiting allows the device to limit the traffic that egresses through a port to a value less than the available link bandwidth. This feature is supported on the 7210 SAS-series platforms.

4.1.1. Applications

This feature is useful when connecting the 7210 SAS to an Ethernet-over-SDH (EoSDH) (or microwave) network, where the network allocates predetermined bandwidth to the nodes connecting into it, based on the transport bandwidth requirement. When connecting to such a network, it is important that the traffic sent into the SDH node does not exceed the configured values, because the SDH network does not have the QoS capabilities and buffers required to prioritize the ingress traffic.

Egress rate attributes include the following.

  1. Per-port configuration of the maximum egress port rate is allowed, using the egress-rate CLI command.
  2. This feature is supported on Ethernet ports.
  3. The scheduler distributes the available maximum egress bandwidth based on the CIR and PIR configuration parameters provisioned for the queues.
  4. Support is provided for a burst parameter to control the amount of burst the egress port can generate.
  5. When ports are members of a LAG, all the ports use the same value for the egress-rate and the max-burst parameters.
  6. If frame overhead accounting is enabled, the queue scheduler accounts for the Ethernet frame overhead.

4.1.2. Effect of Port-Level Rate Limiting on Queue Functionality

When an egress-rate sub-rate value is provided, the queue rates that are specified using percentages use the egress-rate value instead of the port bandwidth (if the egress rate is less than the port bandwidth) to configure the queue rates. Configuring the egress port rate to different values results in a corresponding dynamic adjustment of rates for the queues configured on the ports.

When the egress-rate sub-rate value is set, the CBS and MBS of the associated network queues do not change.

4.2. Basic Configurations

For port-level rate limiting, the following considerations apply.

  1. The egress-rate command is in the config>port>ethernet context.
  2. The egress-rate command configures the maximum rate (in kb/s) for the port. The value should be between 1 and 1000000 kb/s and between 1 and 10000000 kb/s for a 10G port.
  3. The max-burst command configures a maximum burst (in kilobits) associated with the egress rate. This parameter is optional. and if it is not defined, by default it is set to 32 kb for a 1G port and 64 kb for a 10G port. Users cannot configure the max-burst without configuring the egress-rate. The max-burst value should be between 32 and 16384 or the default.
  4. By default, the egress-rate command is not set on the port. The default egress-rate value for a port is the maximum (with is equal to the line rate).
  5. On a 10G port, if the configured egress port rate limiter (ERL) is more than 8 Gig, Nokia recommends configuring the burst value higher than 80 kb to avoid packet drops.

The following is a sample configuration output that shows the egress-rate configuration for a port.

*A:Dut-1>config>port# info 
----------------------------------------------
        ethernet
            egress-rate 120000 max-burst 234
        exit
        no shutdown
----------------------------------------------
*A:Dut-1>config>port#

4.2.1. Modifying Port-Level Egress-Rate Command

To modify egress rate parameters, apply an egress-rate command with new egress-rate and max-burst values.

The following is a sample configuration that shows a modified egress-rate configuration for a port.

*A:Dut-1>config>port# ethernet egress-rate 10000 max-burst default 
*A:Dut-1>config>port# info 
----------------------------------------------
        ethernet
            egress-rate 10000
        exit
        no shutdown
----------------------------------------------
*A:Dut-1>config>port#
 

4.2.2. Removing Port-Level Egress-Rate Command

To remove the egress-rate command from a port, use the no option with the egress-rate command. Do not include the rate for the egress-rate and max-burst options. Use the following syntax to remove the egress-rate command from a port.

CLI Syntax:
config>port>ethernet# no egress-rate

The following is a sample configuration output that shows the removal of egress-rate configuration from a port.

*A:Dut-1>config>port# no ethernet egress-rate
*A:Dut-1>config>port# info 
----------------------------------------------
        ethernet
        exit
        no shutdown
----------------------------------------------
*A:Dut-1>config>port#

4.2.2.1. Default Egress-Rate Values

By default, no egress-rate is configured for a port.