VDX command clarification - fabric trunk/fabric isl enable

[nabromov]

Dear All,

Sorry for the basic question. I am wondering what is the meaning when you have interface, which has 

option 1: 

fabric isl enable 

fabric trunk enable 

Option 2:

fabric isl enable

no fabric trunk enable. 

What would be the difference between both option, if ISL is enable - that means the interface will be used by the fabric, but the trunk part is what is I am not clear about. 

Thank you in advanced.

[Mick_Day · Accepted solution]

Fabric Trunk logically groups ISL ports together to act like a single link with greater bandwidth.  So command 'no fabric trunk enable' prevents these logically grouped links from forming and would instead form individual ISLs

[nabromov]

Thank you for the explanation! Looks like the terminology is a bit different from what I am used to, but it makes sense now.

[Michael_Morey · Accepted solution]

nabromov,

To better understand these commands you have to keep in mind how the VDX and NOS communicates with other VDX devices and fabric formation.  When any VDX device is connected to another ethernet primitives are sent to discover if the far end device is a VDX, what its settings are and it will attempt to form a fabric.

The command "no fabric isl enable" simply stops the last step from happening.  Your VDX will not form an ISL/Join another VDX in a VCS fabric on that port, but the discovery will still happen.  It is recommended that if you have two VDX devices connected and you do not want them in the same fabric, to ensure their "vcs-id" is different along with using the "no fabric isl enable".

If you do choose to establish a fabric, traffic from one VDX destined to an edge port on another VDX will traverse the ISL.  This can cause a bottleneck with more and more occupancy.  To address this, the ISLs will automatically form Trunk Groups which are basically load balanced port channels.  These trunks will only form if they are configured for "fabric trunk enable", the speeds on all the links match, and if they reside in the same physical "port group" on your VDX.  This port range differs per hardware platform, so be sure to check the manuals for your specific device.

If for any reason you do not want two ISLs to automatically form a trunk, you can configure them with "no fabric trunk enable" and they will revert to single links.

Lastly, these commands only impact VCS Fabric and ISL Trunk formation.  Toggling these commands on non VDX<>VDX interfaces should not have any impact on your device.

[Mick_Day · Accepted solution]

Fabric Trunk logically groups ISL ports together to act like a single link with greater bandwidth.  So command 'no fabric trunk enable' prevents these logically grouped links from forming and would instead form individual ISLs