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eduncan911
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New to SPF+: Direct Connect questions

Fri Nov 30, 2018 8:39 pm

Hello, first time poster.

The CRS328-24P-4S+RM has 4x "SPF+" ports. The new-but-not-released CRS312-4C-8XG has 4x "SPF+" combo ports as well.

Can I use some type of "Direct Connect" cable between these two switches for the 10G SPF+ connections? Being new to fiber, I am unsure of the terminology or if this how they are intended to connect.

What I can find is that Mikrotik has a "SFP+ 3m direct attach cable" as well (3m being way too long for my needs). Can I just purchase 1 of these cables and simply plug them in between the switches for 10G links? Is it really that easy - and cheap?

https://mikrotik.com/product/SplusDA0003

Curious, could I connect 2, 3 or even all 4 between these two switches - and use LAG for 40 Gbps between the two switches? :)

I am trying to avoid those expensive adapters, and just want to connect a single inexpensive SPF+ cable between these two devices with a simple cable in a rack sitting on top of each other.
 
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Bergante
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Re: New to SPF+: Direct Connect questions  [SOLVED]

Sat Dec 01, 2018 4:27 pm

Should be as simple as that unless some odd compatibility problem arises.

Those so called DA (direct attach) cables are well known standards. And they are a great solution because the passive ones consume really a tiny amount of power. They just contain a tiny microcontroller to identify themselves (Hi, I am a passive DA cable supporting 10 Gbps, etc) and some passive impedance matching stuff.

The cable is actually twinaxial cable, not fiber.
 
eduncan911
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Re: New to SPF+: Direct Connect questions

Sat Dec 01, 2018 5:29 pm

Should be as simple as that unless some odd compatibility problem arises.

Those so called DA (direct attach) cables are well known standards. And they are a great solution because the passive ones consume really a tiny amount of power. They just contain a tiny microcontroller to identify themselves (Hi, I am a passive DA cable supporting 10 Gbps, etc) and some passive impedance matching stuff.

The cable is actually twinaxial cable, not fiber.
Excellent. Thank you!

So, that would mean these actual "expensive" adapters are the fiber optic versions? Ah, I see now why they would be expensive - converting a digital signal to light, and back again.

And I take it that means there is a limited length you can do with DA/DC due to the twinaxial copper, vs light over long distances. Also, I've heard of lower latency with fiber - so that would make sense as well. In my homelab, latency of gigabit either over RJ45 copper is a non-issue. So yeah, non-fiber works for me with the DC/DA cables.

Am I assuming everything correctly?

Last question: What's typically the max length for these DA/DC cables? I'm curious now of a run about 50 to 80 feet long from the garage rack to my office.

Thanks again!
 
mkx
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Re: New to SPF+: Direct Connect questions

Sun Dec 02, 2018 11:48 am

Typical use for DA cables is interconnection within same cabinet, so they usually come in lengths of a feet or three. For connection with length of 50 to 100 feet fibre is preferred solution (although 10Gbps over UTP cat6/7 or even 5e would work as well over this distance ... fibre might actually be more cost efficient than copper).
BR,
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