Chapter 14. Flow control for Ethernet networks

On an Ethernet link, continuous data transmission can fill buffers and cause network congestion. If the sender’s rate exceeds the receiver’s processing capacity, packet loss can occur due to the switch port’s lower data processing capacity.

The flow control mechanism manages data transmission across the Ethernet link where each sender and receiver has different sending and receiving capacities. To avoid packet loss, the Ethernet flow control mechanism temporarily suspends the packet transmission to manage a higher transmission rate from a switch port. Note that switches do not forward pause frames beyond a switch port.

When receive (RX) buffers become full, a receiver sends pause frames to the transmitter. The transmitter then stops data transmission for a short sub-second time frame, while continuing to buffer incoming data during this pause period. This duration provides enough time for the receiver to empty its interface buffers and prevent buffer overflow.

By default, most of the network drivers in Red Hat Enterprise Linux have pause frame support enabled. To display the current settings of a network interface, enter:

# ethtool --show-pause enp1s0
Pause parameters for enp1s0:
...
RX:     on
TX:     on
...

Verify with your switch vendor to confirm if your switch supports pause frames.