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Ethernet Fabric (VDX, CNA)

Occasional Contributor
Posts: 18
Registered: ‎03-30-2011

Understanding of ISLs


Let's say that I have toplogy where two VDX 6720-60 are connected using 3x10GE ports.

Will this 3 x 10GE ports act as one Layer 2 route path for TRILL of 3 equal Layer 2 paths and then VDX will do ECMP load-balacing to load-share traffic over all 3 10GE ports.

Another question - is it maximum links for single ISL is limited ? As I know ISL have to be in one port group. So It mean that I can have 10 ports for 6720-60 switches and 12 ports for 6720-24 switches.


Retired-Super Contributor
Posts: 260
Registered: ‎05-12-2010

Re: Understanding of ISLs

Hi Rob,

Here are links to blogs that explain how VCS Fabric ISLs form, how Brocade ISL Trunks form and how all that works with ECMP at layer 2.  I hope this is helpful.

Brocade ISL Trunking Has “Almost Perfect Load Balancing”

VCS Technology and Equal Cost Multi-Path for Layer 2

VCS Ethernet Fabric Formation and Brocade ISL Trunks



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