NICs with optical ports: an overview

The other end of every server link is a network interface card (NIC), and it plays the same game as the switch — cages, SerDes lanes, a management bus to the module, a policy about which modules it accepts — with two differences: the policy lives in a driver, not a network OS, and the bottleneck is often the PCIe bus, not the port. This section covers NICs with SFP/QSFP-class cages: the families and vendors, how ports relate to PCIe, transceiver compatibility and its driver-level overrides, the tools that read a module from the server side, and the programmable adapters (SmartNICs, DPUs) that blur the line between card and switch.

What a NIC is, in optics terms

Form factors of the card

Families and vendors

Speeds per card model are fixed by controller and cages; "25G capable" means 10G and 25G, rarely 1G (Ports & PCIe).

What the NIC needs from a module

• Compliance codes for a speed the controller supports at that cage.
• Identity the driver accepts — Intel families are the strict ones (Optics compatibility on NICs).
• FEC/AN behaviour the driver can match: DAC at 25G+ requires Clause 73 AN on both ends; optics need forced speed and matching FEC (FEC & AN).
• Power class within the card's cage budget — most NICs allow QSFP28 class 4 (3.5 W) and QSFP-DD up to 12–15 W; check for ZR/tunable modules (Power & consumption).
• Cooling: server airflow is front-to-back through the card; modules on rear-facing cards sit in exhaust air (Temperature grades).

Typical roles and their optics

Further reading

• NIC ports, speeds and PCIe bandwidth — cages on NICs, dual rate, breakout cables, PCIe generation × lanes vs port totals, OCP 3.0, power and cooling.
• Transceiver compatibility on NICs — driver whitelists by vendor, Intel allow_unsupported_sfp, Windows/ESXi behaviour, FEC/AN with DAC and optics, what to code.
• NIC tools and diagnostics — ethtool -m, mlxlink, bnxtnvm, Intel tools, Windows and ESXi commands, reading DDM and FEC counters from the server.
• SmartNICs and DPUs — BlueField, Pensando, IPU: ports and optics on programmable adapters.

In CodingBox

A module that a NIC rejects is diagnosed the same way as one a switch rejects: read the identity and compliance codes on the bench, compare with the driver's list, code if the policy demands it (Check transceiver, Vendor lock).