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How to check MAC PAUSE counters on all the interfaces of an EX/QFX/MX or a Virtual Chassis

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Article ID: KB23817 KB Last Updated: 21 Oct 2020Version: 5.0
Summary:

This article provides information on what a MAC PAUSE frame is and how to check the MAC PAUSE counters on numerous interfaces of a router, switch or across a Virtual Chassis.

Symptoms:
A MAC PAUSE frame is a bi-directional Flow Control Mechanism implemented to support full duplex operations in the Ethernet standard.

A pause frame allows a device to request other devices on the ethernet segment to halt transmission of traffic temporarily. It does so by specifying the operational code of PAUSE in the MAC control frame along with a timer value indicating the duration of the requested PAUSE. This allows the receiving device to recover from any condition that is leading to congestion (i.e. no buffer space remaining to receive additional frames). Once the specified PAUSE duration expires, the transmitting device can resume the normal transmission of frames.

With flow control enabled, when a device connected to a switch encounters congestion it will transmit a pause frame to the switch, which will be reflected in the mac pause frames counter of the interface extensive command.
Solution:
The following command will display the "MAC pause frames" counters on ALL the interfaces of the Switch or a Virtual Chassis.

NOTE: For individual interfaces use the "show interfaces <interface> extensive" command.
{master:0}
lucianix@SW-ZL> show interfaces "[gfxe][et]-*" extensive | match "physical|pause" 
Physical interface: ge-0/0/0, Enabled, Physical link is Down
    MAC pause frames                         0                0
Physical interface: xe-0/0/1, Enabled, Physical link is Down
    MAC pause frames                         0                0
Physical interface: ge-0/0/2, Enabled, Physical link is Up
    MAC pause frames                         0                0
Physical interface: ge-0/0/3, Enabled, Physical link is Down
    MAC pause frames                         0                0
Physical interface: ge-0/0/4, Enabled, Physical link is Up
    MAC pause frames                         0                0
Physical interface: ge-0/0/5, Enabled, Physical link is Down
    MAC pause frames                         0                0
Physical interface: ge-0/0/6, Enabled, Physical link is Down
    MAC pause frames                         0                0
Physical interface: ge-0/0/7, Enabled, Physical link is Up
    MAC pause frames                       394                0
Physical interface: xe-0/0/8, Enabled, Physical link is Up
    MAC pause frames                         0                0
Physical interface: ge-0/0/9, Enabled, Physical link is Up
    MAC pause frames                         0                0
Physical interface: ge-0/0/10, Enabled, Physical link is Up
    MAC pause frames                         0                0
Physical interface: ge-0/0/11, Enabled, Physical link is Up
    MAC pause frames                         0                0
Physical interface: xe-0/0/18, Enabled, Physical link is Down
    MAC pause frames                         0                0
Physical interface: et-0/0/48, Enabled, Physical link is Down
    MAC pause frames                         0                0
Physical interface: et-0/0/49, Enabled, Physical link is Down
    MAC pause frames                         0                0


You can find Pause frames from Wireshark with the filter "macc.opcode == pause"

You can see "pause_time".
The unit of time is a special unit called "bit quanta". 
If an Ethernet port wants to allow the incoming frame before "pause_time" expires, it can send another Pause frame with pause_time = 0.

Modification History:
2020-10-20: Added example with non-zero MAC pause frames. Modified "show" command to include 40G and 100G interfaces. Added Wireshark capture showing MAC Pause.
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