Arista compatible optics: reading the part numbers and getting the right module

Arista part numbers are unusually readable once you know the pattern — which is fortunate, because an Arista estate typically spans four generations of platform and five or six optical speeds, and the difference between two similar-looking part numbers is often the thing that decides whether a port comes up.

This guide covers how Arista optics are named, which form factor belongs to which platform generation, and what a compatible equivalent has to get right. It is the Arista companion to our existing guides for Catalyst 9300 and 9500, Nexus 9300 and the Juniper QFX5120.

How to read an Arista part number

Almost every Arista optic follows the same three-part shape: form factor, speed, optical interface.

The tail of the part number is the optical interface, and it follows the same IEEE 802.3 conventions as everyone else: SR for short-reach multimode, DR and FR and LR for single-mode at increasing distance, ER and ZR for the long stuff, BD or BIDI for a single-fibre bidirectional pair, and T for copper RJ45.

Arista then adds qualifiers that catch people out:

• -C marks a channelisable module. QDD-400G-SR8-C e OSFP-400G-SR8-C can be broken out into separate lower-speed interfaces; the plain SR8 variants are single 400G ports. If breakout is in the design, the suffix is not optional — our guide to 400G breakout covers what else has to line up.
• -E e -H denote variants with different temperature, reach or platform-support characteristics from the base part. SFP-25G-SR e SFP-25G-SR-E are not interchangeable on every platform.
• -R e -G appear on reversed-airflow and revised builds. OSFP-R-800G-FR4 is not a typo for OSFP-800G-FR4.
• 2FR4, 2LR4, XDR8 and similar indicate a module carrying two independent lower-speed links rather than one aggregated one — QDD-200G-2LR4 is two 100G links, not a single 200G interface.

When you are matching a compatible module to an Arista part number, those qualifiers are exactly where errors happen. The base optical spec is easy; the variant is what determines whether the port accepts it.

Which form factor for which platform generation

Arista’s platform families are consistent enough that the form factor usually follows from the series name:

Two caveats that matter more than the table. First, a QSFP-DD port takes QSFP28 and QSFP56 modules natively, so a 400G-capable leaf can be populated with 100G optics on day one — the backwards compatibility argument we set out in QSFP-DD vs OSFP. Second, OSFP ports need an adapter to take QSFP-family modules, which is an extra part and an extra line on the bill of materials.

Arista-coded optics Carritech stocks

These are tested Arista-coded modules, coded for the platform and ready to insert. It is a representative selection rather than the full list.

1G and 100M

SFP-1G-LX-H for 1000BASE-LX single-mode, and SFP-100M-FX for legacy 100BASE-FX ports. The wider 1.25G duplex SFP range covers the rest.

10G

SFP-10G-SR-H, SFP-10G-LR-H e SFP-10G-ER-H cover 300 m to 40 km, with SFP-10G-ER2 for longer hops. For single-fibre working, SFP-10G-ERBD-U e SFP-10G-ERBD-D are the upstream and downstream halves of a pair — and they must be ordered as a pair, which is the pairing rule explained in our guide to BiDi transceivers. There is also SFP-10G-DWDM for wavelength plans and SFP-10G-T for 10GBASE-T copper. Browse the full 10G SFP+ range.

25G

SFP-25G-SR, SFP-25G-LR e SFP-25G-ER, plus the SFP-25G-SR-E e SFP-25G-LR-E variants. If you are still weighing 10G against 25G at the leaf, our comparison of SFP+ vs SFP28 is the place to start. Full 25G SFP28 range.

40G and 100G

QSFP-40G-SRBD-R runs 40G over duplex multimode where an MPO trunk does not exist. At 100G, QSFP-100G-SR4-E for parallel multimode, QSFP-100G-SRBD for BiDi over duplex OM4, and QSFP-100G-ZR4 for 80 km — the trade-offs are in 100G ZR4 vs LR4 vs ER4. Full 100G QSFP28 e 40G QSFP+ ranges.

200G, 400G and 800G

QDD-200G-2LR4 for two 100G links from one QSFP-DD port. At 400G, QDD-400G-SR8-C in QSFP-DD, or OSFP-400G-SR8 and the channelisable OSFP-400G-SR8-C in OSFP.

At 800G: OSFP-800G-FR4, OSFP-800G-FR4-G and the reversed-airflow OSFP-R-800G-FR4, plus OSFP-800G-VSR8 e OSFP-800G-XDR8. For linear pluggable deployments, LPO-800G-2FR4. Browse the 400G QSFP-DD e 800G OSFP ranges, or the 1.6T transceivers page if you are planning the generation after.

In-rack: cables rather than optics

For server-to-leaf and leaf-to-spine runs inside a rack, two optical modules plus a patch lead is the expensive way to move three metres. A passive direct attach cable does the same job for a fraction of the cost with no lasers to fail, and an active optical cable extends the idea to tens of metres. Our comparison of DAC vs AOC covers where each wins, and you can browse the DAC e DOC ranges directly.

Why coding decides whether the port comes up

An optic’s electrical and optical behaviour is standards-defined — IEEE 802.3 for the Ethernet interface, the SFF specifications maintained through SNIA for the management memory map. What is not standardised is the vendor identification string written into the module’s EEPROM, and that string is what the switch reads on insertion.

A module coded for Arista reports correctly in the interface table, returns full digital diagnostics and generates no unsupported-transceiver warnings. An uncoded or wrongly coded one may be rejected outright. The full mechanism is in our guide to transceiver coding.

If your estate mixes Arista with Cisco, Juniper or Nokia, that string is also what forces you to hold the same optical part four times over. The Carritech Opticode coding box lets you hold one SKU per optical type and code it at the point of deployment instead — the stock argument we set out in building a smarter transceiver stock strategy.

Four checks before you order

1. Match the exact variant, not just the optical type. The -C, -E, -H, -R and -G suffixes exist for a reason.
2. Confirm the EOS version. Newer optics frequently need a minimum software release, and that requirement is per-platform.
3. Check the fibre. SR-family modules need multimode; everything else needs single-mode — see single-mode vs multimode fibre. Parallel optics add MPO polarity to the list, covered in MPO polarity types A, B and C.
4. Work the loss budget before assuming the datasheet distance applies to your link — our guide to optical link budget shows the sums.

Getting Arista optics without the OEM price

Carritech Optics supplies Arista-coded modules across the full transceiver range, from 100M to 1.6T. Every module is coded for the target platform and tested before despatch — see the 22 checks a module passes and our transceiver testing process — and carries a Garanzia a vita, with UK and EU stock and support behind it. If the warranty question is the one holding up the decision, we answer it in do third-party optical transceivers void your warranty?

Have a list of Arista part numbers? Our compatibility checker returns the tested Carritech equivalent in seconds, or send the list over and we will price it — request a quote.