Layer 2 Switching – Can Pause Frames Be Forwarded Through a Layer 2 Managed Switch?

ethernetlayer2switching

I'm not sure this question needs much detail.

I have two Linux hosts connected to a switch with 10 ports. One host has a 10 GbE NIC and the other host has a 1 GbE NIC. Obviously I can flood the 1 GbE card with udp packets. I enable symmetric flow control on the switch for both ports and "as far as I know" have enabled it on the host NICs.

The question now is, when 1 GbE cannot keep up he sends a pause frame to the switch. From what I see, a pause frame can only go Mac-to-Mac.

Therefore, the switch does not forward the pause frame to the host that is pounding the network with traffic. Is that statement true?

Best Answer

A pause frame can be MAC-to-MAC which is host-to-host through a switch. It can also be sent to a special multicast address which a switch will not forward, but the switch itself may or may not participate in ethernet flow control.

The use of ethernet flow control is implementation specific, and not widely or consistently supported. The way it works, or doesn't, on your network is going to be dependent on your network equipment and the software on those devices, and the specific hosts and OSes of the end devices.

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