Arista Optics vs Real World

Just throwing a quick post up to act as a note to myself on Arista’s transceiver form factor names and how they map to the rest of the world. There’s more than what is here, I’m just including the important ones I’m likely to use:

Additional reference for 400gig transceivers and the connectors they use: It also includes some caveats about passive copper cables and legacy equipment.

And the transceiver data sheet:

Finally, mapping for certain fiber requirements:

  • *SR8 transceivers mean 8 optical channels, so MPO-16 APC connectors will be involved, can break out to 2x MPO-12 for 2×200 and 2×100, similar copper options with target QSFP56/QSFP28. I bolded MPO-16 and APC because that seems to be unique to this SR8 transceiver, most Arista MPO connectors are MPO-12, and UPC (not angled)
  • SR8-C, same as above, but fiber can break out to 8×50/25 as well as the default 2×200/2×100
  • SRBD, aka 400G-BIDI aka 400G-SR4.2 – 100m MMF – can break out to 4x100g-bidi and 4x100gig sr1.2
  • DR4/XDR4/PLR4 – longer reach SM fiber with 4 channels, so you’ll be using MPO-12 APC SMF connectors
  • FR4/LR4 – multiplexed SMF, requires standard LC-terminated fiber

QSFP-DD (400 gig) – this one actually matches the industry, Arista QSFP-DD is industry QSFP-DD. They additionally have some interesting breakout options supported, which I’ll outline, and map the form factor industry names.

First, QSFP-DD copper cabling:

  • (1) QSFP-DD of course, including twinax to 2.5m, active optical to 30m
  • (2) 200gig or (2) 100gig copper terminated in “QSFP” (really QSFP56 or QSFP28 respectively, max length 3m/2.5m)
  • (4) 100gig or 50gig copper terminated in “QSFP” (really QSFP28, max length 3m/2.5m)
  • (4) 100gig active copper terminated in “QSFP” (really QSFP28, max length 5m)
  • (8) 25gig copper terminated in “SFP” (really SFP28, max length 2.5m)

QSFP-DD fiber cabling:

  • (1) QSFP-DD with OM4 MMF to 100m on MPO-16 APC connector, which can also break out to 2x200gig and 2x100gig, terminating in MPO-12 connectors
  • (1) QSFP-DD, same as above, but the SR8-C version of the transceiver allows additional breakout cabling to 8x50gig and 8x25gig, all terminating in LC connectors.
  • (1) QSFP-DD, active optical to 30m
  • (2) 200gig or (2) 100gig MMF via MPO-16 to 2x MPO-12 using “SR8” transceiver
  • (8) 50gig or (8) 25gig MMF via MPO-16 to 8x LC using “SR8-C” transceiver
  • (4) 100gig single mode, not seeing SMF equivalents for 8x options

QSFP200 (200 gig) – some Arista devices will have a number of ports described as QSFP200, which is really a QSFP56, which itself is the same physical QSFP port that supports QSFP28/56/112, and is backwards compatible with QSFP+ 40gig physically, but may not support those speeds, so check the model. 200 gig is a weird speed, so you won’t find a lot of breakout options here.

Cabling options:

  • QSFP200 (QSFP56) to the same, twinax 1-3m
  • QSFP200 (QSFP56) fiber, 70-100m over MMF using MPO-12 UPC connector on SR4 transceiver, or 2km over SMF pair with LC connector and FR4 transceiver. There are longer range options as well, but require a very recent EOS version (4.30+)
  • QSFP200 (QSFP56) twinax 1-3m, and twinax to 2×100 QSFP28, and twinax to 4×50 QSFP28 (doesn’t mention if they can drop to 25gig, and there are no explicitly 25gig breakout options, so that may not be possible)

QSFP100 (100 gig) – similar to the above, some Arista devices will have a number of ports described as QSFP100, which is really a QSFP28 supporting 100 and 50 gig speeds, but also backwards compatible to QSFP+ 40gig physically. All devices may not support those speeds, so check the model. For example, the 7280CR3 with (28) QSFP100 ports, (6) QSFP200, and (2) QSFP-DD 400 ports suggests it also supports a total of (36) 40gig, meaning it will indeed accept a QSFP+ in the QSFP28 slot.

Cabling options:

  • All the typical QSFP100 (QSFP28) twinax options up to 5m, active optical to 30m
  • QSFP100 (QSFP28) to 4x25gig twinax to 5m
  • QSFP100 (QSFP28) to 2x50gig twinax to 5m
  • QSFP100 (QSFP28) using SR4 transceiver on MPO-12 UPC to 100m MMF. The Arista transceiver guide does not mention this explicitly, but this transceiver can also break out to 4x25gig using an MPO12 UPC to 4xLC cable. Note, it will NOT do 4x10gig down-rated. If you need to support 4x10gig from a QSFP100 slot, you need their 40gig QSFP+ SR4 transceiver.
  • QSFP100 (QSFP28) similar to above SR4, there’s a PSM4 for doing the same breakout with single mode; 4x25gig LR using MPO-12 to 4xLC
  • Fiber SRBD (bidi) on LC OM4 to 100m, and then lots of normal SMF options

QSFP+ (40 gig) – this one is standard, and Arista fortunately also calls it QSFP+. It’s really not used that much these days but the reason I’m including it here is to note that if you need to do 4x10gig on a device that has QSFP100 slots, you must use the QSFP+ 40gig SR4 transceiver to accomplish that, the faster 100gig SR4 will only break out to 4x25gig. That will be the QSFP-40G-SR4, which uses an MPO-12 UPC to 4xLC cable.

SFP – this is a tough one. Arista models that support 100gig on down in the SFP format will typically just call all the ports “SFP” on the data sheets. However, depending on the model, these ports may be usable for 100 gig SFP-DD transceivers, 50gig SFP56 transceivers, 25gig SFP28 transceivers, 10gig SFP+, and even 1gig SFP. If supported, the slower speeds may require locking the ports, or a group of ports, to a specific speed. You have to be very careful when doing this because if you change the speed of a member of a group, it may turn them all off until you correct the mismatch. Only the 100gig options have breakout cables, which only show as 2×50.

Leave a Reply

Your email address will not be published. Required fields are marked *