branded DAC cables?

[tubs-ffm]

Hello,

I know that there are branded versions of SFP and SFP+ fibre modules, and that some switches are more or less strict about accepting these.
But what about DAC cables for SFP, SFP+ and SFP28? Do I need to consider brand compatibility?

Specifically, I want to connect a Ruckus ICX 8200 switch to a Mellanox ConnectX-4 network card via a passive DAC cable.

 

[alaricljs]

DACs have no coding. The only integrated cable w/ coding would be an AOC which is a unified set of 2 SFPs and an optical cable.

 

[tubs-ffm]

DACs have no coding. The only integrated cable w/ coding would be an AOC which is a unified set of 2 SFPs and an optical cable.

This is what I thought. But when I was scrolling through the FS shop I found this configuration option it in their configurator.

https://www.fs.com/eu-en/products/65841.html?now_cid=2869

 

[nexox]

Many NICs and some switches which enforce vendor matching on fiber modules are more relaxed about DACs, but the eeprom with vendor data is still present (excerpt from ethtool -m on an interface on my desktop running a 10GTek DAC coded for Intel):

    Vendor name                               : Intel Corp
    Vendor OUI                                : 00:40:20
    Vendor PN                                 : 821-24-011-02

In any case the ConnectX-4 won't care about any module coding and I doubt the Ruckus requires a DAC to match.

 

[klui]

@nexox is correct about DACs having cable coding. In fact, the VDX6740T doesn't permit Mellanox DACs to be used.

I do find that CX4s/CX5s are more restrictive than CX3s when it comes to modules: if they are 100G and you want to use them at 40G. No problems with CX3s. I keep on forgetting the nuance but I think that's the jist.

 

[Shonk]

They do have coding in DAC's here's my two

 

[tubs-ffm]

Thank you.
It looks like I have to play a little bit like lottery to se if it finally works in my combination.

 

[AICPLIGHT]

Yes, brand compatibility is definitely required for SFP, SFP+, and SFP28 DAC cables, as network switches like the Ruckus ICX 8200 typically check the cable's internal programming (EEPROM) for vendor lock-in before activating the port.

 

[i386]

At home I never ran into problems with dac cables (arista, mellanox, brocade/ruckus & mikrotik switches), but I usually run the commands to enable third party support before deploying switches.

There was an older thread and somebody posted that switches are more "relaxed" with dac cables because that might be the only thing that is available and you have to make a network work with different switches in a datacenter/enterprise

 

[Greg_E]

There was an older thread and somebody posted that switches are more "relaxed" with dac cables because that might be the only thing that is available and you have to make a network work with different switches in a datacenter/enterprise

Some brands do not care if your system is down... We'll send someone right over with parts in hand, for a cost.

 

[tubs-ffm]

Thank you for all the information.
In every case I can confirm that my combination is working:
- Switch Ruckus ICX 8200
- NIC Dell 00M95 (Intel XXV710-DA2)
- Kabel FS passive DAC with coding "generic"

 

[blunden]

There was an older thread and somebody posted that switches are more "relaxed" with dac cables because that might be the only thing that is available and you have to make a network work with different switches in a datacenter/enterprise

Yes, I believe that is the case for some manufacturers, but not necessarily all of them. I base that on the fact that there still seems to be a market for third party DAC cables with different vendor coding on each end from FS.com, FlexOptix, etc.

It supposedly applies to some NICs too, such as vendor locked Intel NICs, if I recall correctly.

 

[Greg_E]

If you are going to go to optics, does a DAC make sense anymore? I know there are longer DAC that are optical, but it seems you would be better off just going to a "normal" optical module once you extend beyond the 4 meters or so of the longest passive cables I've seen.

Only case where this may not apply is SFP-DD which is the stacking cable that is used on my Extreme 5420m switches. They offer up to a couple meters in standard, then to a "special" optical SMF (LC connectors) module for larger distances.

 

[tubs-ffm]

So for ICX 8200 ConnectX-4, a normal passive SFP+/SFP28 DAC should work.
Optics are where vendor lock-in usually shows up, not DACs.

Thank you.
Meanwhile I went a different way - Intel XXV710 instead ofConnectX-4.
This is working as well. --> #11

 

[tubs-ffm]

If you are going to go to optics, does a DAC make sense anymore?

DAC makes sense where you have short distances like devices standing next to each other.
They are robust and cheaper.

I know there are longer DAC that are optical, but it seems you would be better off just going to a "normal" optical module once you extend beyond the 4 meters or so of the longest passive cables I've seen.

These are not called DAC (= Direct Attached Copper).
A good overview and comparison between DAC, AOC and AEC you can find here:
Understanding DAC, AOC, and AEC Cables: A Comprehensive Guide - STORDIS GmbH

 

[i386]

If you are going to go to optics, does a DAC make sense anymore?

Like many things related to life and IT: "it depends" ._.
With an unlimited budget and availability: no it doesn't make sense, get everything for single mode fibers and lc-lc connectors
With limited budgets/availability it could make sense to get dac cables ._.

 

[blunden]

If you are going to go to optics, does a DAC make sense anymore?

For short distances where you're able to use passive DACs, yes. Passive DACs are cheaper, lower power and slightly lower latency (due to a lack of signal conversion on each end).