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[QFX] Actual speed of em0 interface not displayed in "show" output



Article ID: KB35459 KB Last Updated: 05 Feb 2020Version: 1.0

On QFX Series switches, the interface speed of a management port may not be reflected properly in the show command output due to a product limitation. This behavior is explained in this article and a workaround is also provided.



The actual interface speed of the em0 port is not displayed in the show interfaces em0 output on QFX Series switches. For example, when the em0 port is connected to a 100m-speed peer, the port's speed is displayed as 1000 mbps even though the actual em0 interface speed is 100m.

A sample output is as follows:

test@QFX5100> show interfaces em0 extensive | match speed
  Type: Ethernet, Link-level type: Ethernet, MTU: 1514, Clocking: Unspecified, Speed: 1000mbps

In the show command output, the speed of the em0 interface is always shown to be a fixed value of 1000 mbps.



This is a limitation on all platforms that run Junos VM on a CentOS/Linux host. Because the command output is coming from a virtual network port and not the physical interface, there is no support for changing the link speed of the virtual port.



To check the actual speed, log in to the host shell and check the speed of the eth0 port.


  1. Log in to the system as the root user.
  2. On Command Line Interface (CLI), issue the request app-engine host-shell or the hshell command in shell mode to get to the host shell.

root> request app-engine host-shell

root@QFX5100:RE:0% hshell
  1. Issue the ethtool eth0 command on the host shell and check the interface speed.
-sh-4.1# ethtool eth0
Settings for eth0:
            Supported ports: [ TP ]
            Supported link modes:   10baseT/Half 10baseT/Full
                                    100baseT/Half 100baseT/Full
            Supports auto-negotiation: Yes
            Advertised link modes:  10baseT/Half 10baseT/Full
                                    100baseT/Half 100baseT/Full
            Advertised pause frame use: Symmetric
            Advertised auto-negotiation: Yes
            Speed: 100Mb/s
            Duplex: Full
            Port: Twisted Pair
            PHYAD: 5
            Transceiver: internal
            Auto-negotiation: on
            MDI-X: Unknown
            Supports Wake-on: pumbg
            Wake-on: g
            Current message level: 0x00000003 (3)
            Link detected: yes


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