Data Center (VDX)

 VDX6740T-1G can ISL be configured on the 1g ports ?

Phil.f's profile image
Phil.f posted 11-12-2019 10:44


We have a 4 switch fabric, 2 of which are VDX6740T-1G with just the base licence, so apart from the 40G QSFP we have only 1G ports.

This was deployed by other engineers in the past, and I now have to troubleshoot issues we are seeing on a number of these 1G ports.

I notice in the interface configuration, the 1G ports have fabric isl enable, and fabric trunk enable configured although from the documentation ISL seems to be only for 10G enabled ports.

Should these two commands be no fabric isl enable, and no fabric trunk enable the 1G ports, or are the commands just ignored on 1G interfaces ?

Issues are that ports on both switches have gone into an up/down state. Also others are up/up but no longer transmit traffic.

Many Thanks in advance,




joergkost's profile image

Only 10G / 40G can join the ISL fabric, the state of the “fabric isl” - commands on that interfaces shall be ignored.


Did you check for a 10G license on that switches that may have been removed / voided?

show license


How are these VDX6740T-1G  switches supposed to be connected to the other  switches?
show running-config interface

Also to check the health of that fabric switches:

show fabric islports 

show fabric


Michael Morey's profile image
Michael Morey

To further expand on this:


The configurations:

fabric isl enable

fabric trunk enable 

are default for all ports on NetworkOS switches. 

Negating the first command will simply put an ISL in Admin Down status.  Negating the second will stop the ISL from attempting to form a trunk with other ISLs in the same port group.  As previously stated, these commands are ignored on a 1Gbps link as ISLs are supported on 10Gbps and  up.


Also configuring any port as a “switchport” will cause these commands to be ignored on a port of any speed.


If you are looking into a licencing issue I would also recommend you use the command:

show dpod

This will tell you all the ports that are assigned to your base switch licence as well as any add on licence you have installed.  With that said I doubt you have a license issue.  Ports that are not licensed can be configured, however once the “no shutdown” command is issued the port will automatically remove all configuration and revert to the Admin Down state.


If your ports are UP/Down or UP/UP and not transmitting traffic I would recommend looking into a Layer 2/control plane issue and/or a config issue.  Also it is possible that the ASIC could be encountering Parity Errors which you can verify with the following:

unhide foscmd
[root password]
fos bash
errdumpall | grep ASIC

If you are seeing a pattern of regularly occurring ASIC errors please reload your switch and confirm if the issue persists.


If you need further support I would recommend contacting our support department and creating a case for us to look into.



Michael Morey 
Principal Technical Support Engineer – Switching, Routing & Analytics