Some 10-Gig network gear requires proprietary cabling

Dec. 19, 2011
Blogger uncovers anomalies with direct attach copper assemblies and gets Cisco to admit they're against cables in the data center.

Howard Marks, who blogs for deepstorage.net and Network Computing, recently exposed the reality that some 10-Gbit/sec switches will function properly only if the cabling plugged into them is a specific brand. Generally, that brand is their own. As the name of Marks's site suggests, he is talking about storage networks within data centers.

In a post dated December 1, Marks explained, "As I brought my Brocade 8000 switch up and started using it, I've had a few hiccups that led me to believe things weren't as simple as I hoped. Frankly, vendors are at fault. 10-Gbps twinax Direct Attach Copper (DAC) cables seemed to be the answeer. When Brocade so kindly lent me the switch, it provided two Brocade-branded cables and a handful of 10G-SR optics. Not wanting to be a piker, I ordered additional cables from Amphenol Cables on Demand ...

"When I tried using the cables, the switch said they were invalid SFPs. A little research ... showed that Brocade supports only active DAC. I had bought passive. ... I then read the Brocade 8000 FAQ, which says that the 8000 supports only Brocade-branded SFPs. I read this to mean that if I bought Molex active cables - which by the way are what Brocade sells, although Brocade has Molex change the identifier to Brocade - they wouldn't work, either."

His blog further says that other equipment "will make a best effort with whatever you plug into them," but still others will go as far as crashing if the wrong active cable is plugged into them.

You can see Marks's December 1 entry in its entirety here.


His follow-up, posted here at Network Computing on December 15, was entitled "The Cable Conundrum Continues - Vendors Respond." It is based on Marks's pursuit of the issue through which he asked 10-Gbit networking vendors about their support of active and passive direct-attach copper cables. As he points out in the post, Cisco provided an interesting response: "'At Cisco, we have a very straightforward view on cables - we're against them! Specifically, we believe that data centers should deploy as few cables as possible.'" For his part, Marks commented, "This is a sentiment I can agree with completely."

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