Thursday, June 9, 2016

Brocade vs Cisco: VDX/Nexus Etherchannel (Port-Channel) Utilization

You know, I've been meaning to write about this for a while now.  There is this misconception about etherchannel link utilization that is going around.  Meaning, if you have a port-channel configured with a few connections in a Cisco Nexus datacenter gear, don't think that all links will be utilized equally.  Cisco uses "flow based" load balancing (hash based) to get data across the port-channel.  So, flow #1 might be utilizing 90% of the first link in the port-channel, where the flow #2 might be using 5% of the second link in the port-channel, and flow #3 might be using 30% of the third link.  Sure, you get the redundancy, and the bandwidth is technically there.  But that doesn't mean that the load is evenly distributed across all links in the port-channel like you might think.  This is handled in the IOS software.  Flow based load balancing inherently results in point congestion and packet drops on single physical links without the capability of using unutilized capacity on additional links between the same switches.
In comes the Brocade VDX.  The VDX actually DOES do "frame-level based" load balancing across its ISL links (trunk link).  And, this actually does allow for full utilization of the bandwidth of a port-channel (called a trunk in Brocade).  This is handled in the ASICs (hardware) instead of the software, and its Brocade proprietary.  
If you want to learn more about the Brocade VCS solution for data centers, then click on this link to download "Brocade VCS Fabric Technical Architecture" paper.  I highly recommend it.


  1. Wow! Very interesting! My understanding as to the reasoning behind flow (hash) based port-channeling is so that no packets will arrive out-of-order, which some applications can't handle well. So, Brocade has figured this out? I'm downloading their white paper right now...thanks!

    1. Yeah, brocade has figured it out. If I'm not mistaken (I'll have to verify), I think they control it on the sending end. Good stuff.

  2. is brocade icx switch support this types of feature ?


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