AOC noob questions | ServeTheHome Forums

I have experience with 10G SFP+ and 100G QSFP28 passive DAC cables but have absolutely no experience with optical cables.

I need to connect one ConnectX-5 Ethernet card to another (both have 100G QSFP28 ports) but I believe the systems are too far apart (approx 10 meters) for passive DAC cables.

I'm thinking of getting an AOC to handle the longer distance.

Questions:

1. Is there anything special I need to know / watch out for with AOCs besides making sure the ends are "coded" for the intended card manufacturer?
2. Is there any downside to ordering a longer cable (say 15m instead of 10m) than I need?
3. Any sources you recommend that can deliver to the US West Coast in a week or so?

Thanks in advance! You should be good, I've used various AOCs and transceivers with ConnectX-4s, QLogic Fastlinq NICs, and a Celestica DX010 Switch.

If you buy AOCs/QSFPs sold as Mellanox-compatible from a reputable supplier like fs.com I don't expect you to have any problems.

One thing to consider with 100G in general is the FEC mode, but with a short (not km), direct (no switch) run in your case I don't think it matters at all.

There is no downside to using a longer cable, except higher cost and needing to manage the slack.

Another option you could consider is CWDM4 transceivers. They connect with 2xLC SM. This would let you run any length of cheap duplex SM fiber you want, change it in the future, replace the run if it breaks, etc. I run the Kaiam XQX 100G-CWDM4-RT bought from eBay.

Supplier-wise, fs.com is usually a safe bet, though I'm not sure about shipping times. I've had good success buying from eBay, but YMMV on that one.

The one AOC I had a problem with compatibility-wise is this HPE-branded Finisar one:

Code:

Ethernet99: SFP EEPROM detected
        Application Advertisement: N/A
        Connector: No separable connector
        Encoding: 256B257B
        Extended Identifier: Power Class 4(3.5W max), CDR present in Rx Tx
        Extended RateSelect Compliance: QSFP+ Rate Select Version 1
        Identifier: QSFP28 or later
        Length Cable Assembly(m): 10
        Nominal Bit Rate(100Mbs): 255
        Specification compliance:
                10/40G Ethernet Compliance Code: 40GBASE-SR4
                Extended Specification compliance: 100G AOC (Active Optical Cable) or 25GAUI C2M AOC
        Vendor Date Code(YYYY-MM-DD Lot): -09-09
        Vendor Name: FINISAR CORP
        Vendor OUI: 00-90-65
        Vendor PN: FCBR425QE1C10-HP
        Vendor Rev: A
        Vendor SN: 8CZ

I couldn't get that to work at 100G... But it works perfectly on my HP-branded 4x25G quad NIC, so it's probably some kind of vendor lock-in. If you're buying new this won't be an issue for you.

Dave

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