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Configuration Guide - Interface Management
CloudEngine 12800 and 12800E V200R003C00

This document describes the interface management configuration, including basic interface configuration, Ethernet interface configuration, and logical interface configuration.

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Configuring Flow Control

Configuring Flow Control

Context

Network congestion causes packet loss. Flow control is a method of avoiding packet loss. If network congestion occurs on the local device after flow control is configured on both ends of the link, the local device sends a message to the peer device, instructing the peer device to reduce the packet sending rate. After receiving the message, the peer device stops sending packets to the local device no matter whether its packet sending rate is high or low, which prevents congestion.

As shown in Figure 2-2, SwitchA communicates with SwitchC through SwitchB. The flow control function is implemented as follows:
  1. 10GE1/0/1 on SwitchA is connected to 10GE1/0/2 on SwitchB, and the auto-negotiation speed is 10000 Mbit/s. The interfaces send data packets to each other at the speed of 10000 Mbit/s.
  2. The outbound interface GE1/0/1 on SwitchB only provides a maximum transmission speed of 1000 Mbit/s. When congestion occurs during packet forwarding, SwitchB caches the received packets. When the number of cached packets exceeds the forwarding capability of GE1/0/1, packet loss may occur.
  3. After flow control is configured on 10GE1/0/1 of SwitchA and 10GE1/0/2 of SwitchB, 10GE1/0/2 sends a Pause frame to 10GE1/0/1, instructing 10GE1/0/1 to stop sending packets. After receiving the Pause frame, 10GE1/0/1 stops sending packets to 10GE1/0/2 within the period specified in the Pause frame. If congestion still occurs, 10GE1/0/2 continues to send Pause frames to 10GE1/0/1.
  4. GE1/0/1 continues sending the cached data packets until congestion is eliminated.
  5. After congestion is eliminated, SwitchB no longer sends Pause frames to SwitchA. SwitchA then can continue to send data packets at the speed of 10000 Mbit/s.
Figure 2-2 Flow control

You can enable flow control in both the inbound and outbound directions of an interface or enable the function in either direction based on actual requirements. For example, if flow control is enabled in the inbound direction of 10GE1/0/1 on SwitchA, the interface is controlled by the remote interface and stops sending data packets after receiving a Pause frame from the remote interface. If flow control is enabled in the outbound direction of 10GE1/0/1, the interface only sends a Pause frame to the remote interface, instructing the remote interface to stop sending packets. If the inbound and outbound directions are not specified, flow control is enabled in both directions.

When the peer device does not support auto-negotiation, you can configure flow control on two ends of the link. When the devices on two ends of the link both support auto-negotiation, you can configure flow control auto-negotiation on the two ends. The local device then negotiates with the peer device to determine whether flow control is enabled based on the network congestion status.

  • Flow control and flow control auto-negotiation cannot be configured concurrently.

  • Flow control and flow control auto-negotiation can take effect only when being configured on both ends of a link.

NOTE:
  • For the flow control function supported by Ethernet interfaces, see Interface Query Tool.

  • Ensure that no loop exists on the traffic path when enabling the flow control function; otherwise, traffic may fail to be forwarded. Flow control does not take effect for traffic on the following loopback interfaces:
    • Loopback interface on the TRILL gateway

    • Loopback interface of VXLAN services

    • Outbound interface configured with MQC (traffic statistics)

    • Outbound interface configured with MQC-based traffic policing

Procedure

  • Configure flow control.
    1. Run system-view

      The system view is displayed.

    2. Run interface interface-type interface-number

      The interface view is displayed.

    3. Run flow-control [ input | output ]

      Flow control is configured.

      By default, flow control is disabled on an Ethernet interface.

    4. Run commit

      The configuration is committed.

  • Configure flow control auto-negotiation.

    1. Run system-view

      The system view is displayed.

    2. Run interface interface-type interface-number

      The interface view is displayed.

    3. Run undo negotiation disable

      The Ethernet interface is configured to work in auto-negotiation mode.

      If the interface by default works in auto-negotiation mode and the working mode cannot be modified, you do not need to perform this step.

    4. Run flow-control negotiation

      The flow control auto-negotiation function is configured on the interface.

      By default, flow control auto-negotiation is not configured on the interface.

    5. Run commit

      The configuration is committed.

  • Configure flow control and threshold parameters for flow control.
    1. Run system-view

      The system view is displayed.

    2. Run interface interface-type interface-number

      The interface view is displayed.

    3. Run flow-control [ input | output ] buffer { xon xon-value | xoff xoff-value } *

      Flow control is enabled on an Ethernet interface and threshold parameters for flow control are configured.

      By default, flow control is disabled on an Ethernet interface.

    4. Run commit

      The configuration is committed.

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Updated: 2019-05-05

Document ID: EDOC1100004195

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