4. Port Level Egress Rate-Limiting

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

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 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, since the SDH network does not have QoS capabilities and buffers required to prioritize the ingress traffic.

Egress rate attributes include:

  1. Allows for per port configuration of the maximum egress port rate, 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, then 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 will 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. Manual configuration of the egress port rate to different values will result 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 will 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

To apply port level rate-limiting, perform the following:

  1. The egress-rate command is present in the *A:Dut-1>config>port>ethernet context.
  2. The egress-rate configures the maximum rate (in kbps).

By default, there is no explicit egress-rate command set on the port and the port operates at the maximum line-rate speed it is operating at.

The following is a sample egress-rate configuration output 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 you can simply apply a egress-rate command with new egress-rate.

4.2.2. Removing the Port-Level Egress-Rate Command

To remove the egress-rate from a port, use the no option with the egress-rate command. The rate for the egress-rate option and max-burst should not be used in this case.

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

The following is a sample 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#