Twinax trivia check (was Re: Is there such a thing as a 10GBase-T SFP+ transciever)

Murphy-Olson, Daniel E. dolson at
Sun Feb 2 22:49:23 UTC 2014

Most of the switch vendors have an "official" compatibility list, but I've found that generally the most common compatibility issue is active vs passive twinax. 

Brocade edge switches and nics are normally active only, which seems to come up a lot - because most short cables are passive unless they are brocade branded.  >5m is normally the cutoff for passive twinax.  Pretty much everything else I've encountered supports passive.

For a while, the intel x520 nics, which are very common, didn't support active connections - but they have since released firmware that fixes this problem.  
Netapp's lower end gear doesn't support active twinax.  

From: Jeff Kell [jeff-kell at]
Sent: Sunday, February 02, 2014 3:15 PM
To: Bryan Tong; Jay Ashworth
Subject: Re: Twinax trivia check (was Re: Is there such a thing as a 10GBase-T SFP+ transciever)

On 2/2/2014 4:03 PM, Bryan Tong wrote:
> These cables are most commonly known as "Direct Attach Copper SFP+"

The big issue appears to be that these are not always "consistently
functional" crossing vendor lines (sometimes product lines within the
same vendor).  There does not appear to be any standardization in
place.  Not sure how much of this is picky vendor software looking for
"branded" marks in their transceivers (e.g., Cisco "service
unsupported-transceiver") versus true incompatibilities.

We have had issues in test cases crossing vendor lines (Cisco / Brocade
/ Dell / HP) with a "twinax" link that just simply won't work.  If
anyone has a clear explanation or better understanding, I'm all ears.
Personal experience comes from only a few testbed cases.


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