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 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 to 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. Ethernet ports configured as access and access uplink support this feature.
  3. The port scheduler distributes the available maximum egress bandwidth based on the CIR/PIR configuration parameters provisioned for the queues.
  4. The burst parameter is not user-configurable and is set to a default by software.
  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 (also known as frame-based accounting) is enabled, the queue scheduler accounts for the Ethernet frame overhead.
  7. When an egress-rate sub-rate value is given, the access-uplink port egress queue rates that are specified using percentages will use the egress-rate value instead of the port bandwidth to configure the appropriate queue rates if the egress rate is less than the port bandwidth. Configuration of egress port rate to different values will result in a corresponding dynamic adjustment of rates for the egress queues configured on access-uplink ports.
  8. On the 7210 SAS-K 2F6C4T and 7210 SAS-K 3SFP+ 8C, when an egress-rate sub-rate value is given, the network or hybrid port egress queue rates that are specified using percentages use the egress-rate value instead of the port bandwidth to configure the queue rates if the egress rate is less than the port bandwidth. Manually configuring the egress port rate to different values results in a corresponding dynamic adjustment of rates for the egress queues that are configured on the network ports.
    For hybrid ports, port queue rates specified as a percentage in the QoS policy change based on the lowest values of nw-egr-agg-shaper-rate, egress-rate, or the port bandwidth.
  9. When the egress-rate sub-rate value is set, CBS/MBS of the associated network queues is not modified automatically. The user has an option to change the CBS/MBS values if necessary.

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).

By default, the egress-rate command is not set on the port, and the port operates at the maximum line-rate speed it is operating at.

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
        exit
        no shutdown
----------------------------------------------
*A:Dut-1>config>port#
 

4.2.1. Modifying the Port-Level Egress-Rate Command

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

4.2.2. Removing the 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 the 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#