flow-control (interface view)

Usage Scenario

Flow control prevents packet loss caused by network congestion. If network congestion occurs on the local device after flow control is configured, the local device sends a message to the remote device, requesting the remote device to temporarily stop sending packets. After receiving the message, the remote device temporarily stops sending packets to the local device regardless of the interface working rate. In this case, the device can receive and send pause frames.

Precautions

• If flow control is enabled on an interface, it must also be enabled on the peer interface.

• Flow control and flow control auto-negotiation can be configured on Ethernet interfaces, but they cannot be configured concurrently.

• XGE interfaces on the S5720-32C-HI-24S-AC, the first 12 XGE interfaces on the S6720-50L-HI-48S, and XGE interfaces and the last eight GE interfaces on the S5720-56C-HI-AC, S5720-56C-PWR-HI-AC, and S5720-56C-PWR-HI-AC1 do not support flow control.

• When an interface works in half-duplex mode, flow control does not take effect on the interface.

• In a scenario where Layer 3 services are deployed, enabling flow control may affect the IP traffic forwarding on the interface. As a result, the interface becomes unavailable. You can run the undo flow-control command in the interface view to disable flow control to recover the interface.

• If the flow control configuration is implemented on the S6720-SI and S5730-SI using the flow-control command, the rate limit for outbound traffic of the GE electrical interface is 200 Mbit/s, and a congestion occurs, the inbound traffic rate cannot be reduced to be the same as the outbound traffic rate on the GE electrical interface. (The inbound traffic rate is about 200 Mbit/s.)
• Traffic control configured when traffic on a 40GE or 10GE outbound interface of the S5730-HI is congested takes effect after a period of time. The waiting time is calculated as follows: Actual buffer size of the interface/Traffic shaping value of the interface. In an extreme case, for example, the traffic shaping value of a 40GE outbound interface is set to 64 Kbit/s, the maximum buffer size of the interface is 128 KB (1 kB = 8 kb), and traffic control takes effect after 16 seconds. If traffic control conditions are met in other cases, flow control takes effect immediately.
• For the S5735-L, S5735S-L, S5735S-L-M, S5735-S, S5735-S-I, and S5735S-S, the multicast functions (both Layer 2 and Layer 3 multicast functions) conflict with the flow control function.