---
title: "EEPROM Programming for Compatible Transceivers: What Gets Written and Why It Matters"
slug: "transceiver-programming-eeprom-guide"
type: tutorial
category: "Compatibility & Programming"
tags: [EEPROM, transceiver programming, compatible transceivers, SFP, QSFP, NOS validation, Flexoptix, vendor name, OUI, compatibility]
seo_focus_keyword: "transceiver EEPROM programming compatible"
---

Every optical transceiver carries a small non-volatile memory — the EEPROM — that contains the module's identity, performance parameters, and operational data. When a switch inserts a module, it reads this memory before deciding whether to accept or reject the transceiver. Understanding exactly what gets written into that memory, how NOS platforms use it, and what a well-programmed compatible module looks like is the technical foundation for why EEPROM customization matters in practice.

## The EEPROM Structure

For SFP and SFP+ modules, the memory map is defined in SFF-8472 ("Diagnostic Monitoring Interface for Optical Transceivers"). The primary data occupies two 256-byte address pages at I2C addresses A0h and A2h. The A0h page contains static identity and specification data. The A2h page contains real-time diagnostic values — temperature, voltage, laser bias current, TX power, RX power — updated continuously.

For QSFP and QSFP+ modules, the memory map is SFF-8636. For QSFP-DD and OSFP (400G and above), the map is defined in CMIS (Common Management Interface Specification), which adds module-level state machines for initialization and firmware update. CMIS is significantly more complex than SFF-8636 and introduced several new fields that NOS platforms check before allowing module operation.

The identity fields in A0h that matter most for NOS acceptance:

**Byte 0: Identifier** — Module type identifier. 0x03 = SFP/SFP+, 0x0D = QSFP+, 0x11 = QSFP28, 0x18 = QSFP-DD. A module with the wrong identifier byte will fail type validation immediately.

**Bytes 20-35: Vendor Name** — 16-byte ASCII string, padded with spaces. This is the field that contains "CISCO-FINISAR" on Cisco-branded modules, "JNPR-FINISAR" on Juniper-branded modules, or "FLEXOPTIX" on Flexoptix modules. NOS platforms that enforce vendor whitelisting check this field against an approved vendor list.

**Bytes 37-39: Vendor OUI** — 3-byte IEEE organizationally unique identifier. This is the manufacturer's registered OUI, used as an additional authentication layer on some Cisco and Arista platforms. A module claiming to be "CISCO" but with an OUI not assigned to Cisco's photonics division will fail OUI validation.

**Bytes 40-55: Vendor Part Number** — 16-byte ASCII string. This must match a part number in the NOS compatibility database for the module to be accepted on platforms with strict PID checking. Cisco uses this to implement their "Type 1" vs "Type 2" transceiver policy.

**Bytes 68-83: Serial Number** — 16-byte ASCII string. Must be unique per module; some NOS platforms log serial numbers and will flag duplicates.

**Byte 84-91: Date Code** — 8-byte date string in YYYYMMDD format. Some platforms check that the manufacture date is within a reasonable window (not dated in the future, not suspiciously old).

**Bytes 92-94: Diagnostic Monitoring Type, Enhanced Options, SFF-8472 Compliance** — Flag bytes indicating what diagnostic features are supported. A module that claims SFF-8472 Rev 11.4 compliance but doesn't respond correctly to A2h reads will cause NOS monitoring systems to report errors.

## How NOS Platforms Validate Modules

The validation logic varies substantially by vendor and platform. Understanding the failure modes helps diagnose acceptance issues.

**Cisco IOS-XE / NX-OS** implements a multi-layer check. First, the identifier byte must be in the supported module type list for the port. Second, if the vendor name starts with "CISCO" or matches a known OEM alias, the OUI is validated against Cisco's registered range. Third, the vendor part number is checked against a PIDs database maintained in the switch firmware. Fourth, Cisco platforms running "service unsupported-transceiver" bypass layer 2 and 3 checks but not layer 1 (identifier type must still match).

The practical implication: a compatible SFP28 programmed with Cisco-compatible vendor name and a valid part number from Cisco's documentation will pass all four checks without requiring service unsupported-transceiver. A generic module with vendor name "GENERIC" or "OEM" will fail at layer 2 and require the bypass command.

**Juniper Junos** reads the EEPROM for informational purposes but does not whitelist-reject modules based on vendor name on most platforms. Junos will log "Vendor: OEM TRANSCEIVER" in the chassis hardware output but will bring the port up. The exception is platforms with Juniper's "Enhanced" chassis management features, where PID validation is more strict.

**Arista EOS** is similar to Junos — module acceptance is based on signal integrity (can the port lock and stay locked?) rather than EEPROM content, with EEPROM data used for inventory and telemetry. The show interfaces transceiver command displays all EEPROM fields. Mismatched fields produce informational warnings, not rejection.

**Nokia SR OS** on 7750/7450 series routers has historically been more permissive than Cisco but less permissive than Arista. Nokia uses a "qualified optics" database concept for their high-end chassis; unqualified modules work but generate system log messages.

## What "Flexoptix Programming" Means Technically

The Flexoptix programming service writes all identity fields to match the target platform's expectations. For a Cisco Nexus 93180YC-EX deployment, this means:

- Vendor Name: "CISCO-INNOLIGHT" or the specific OEM alias that Cisco's NX-OS version expects
- Vendor OUI: Cisco's registered OUI (00:00:0C or the photonics division OUI)
- Vendor Part Number: A valid Cisco PID from the platform compatibility matrix for that module type
- Serial Number: A unique value that won't collide with other modules in the same chassis
- Date Code: A plausible manufacture date
- All diagnostic monitoring flags set correctly for the module's actual capabilities

The EEPROM write is done on Flexoptix's proprietary programming hardware (the PROTEUS programmer) which supports all current SFP, SFP+, QSFP, QSFP28, and QSFP-DD form factors. The programming is non-destructive in the sense that the actual optical parameters — calibration constants, alert thresholds, real-time monitoring coefficients — are not modified. Only the identity fields change.

## Why a Well-Programmed Compatible Is Better Than a Badly-Cloned OEM

A badly-cloned compatible transceiver — one that copies the serial number, part number, and date code of a specific OEM unit — creates two problems that a properly programmed compatible avoids.

First, serial number collision: if two modules have the same serial number and both appear in a network management database, inventory tracking breaks. Some NOS platforms will generate hardware fault alarms when they detect duplicate serial numbers in the same chassis.

Second, diagnostic monitoring integrity: a cloned EEPROM may copy calibration constants from the donor module that are specific to that donor's optical components. A different laser with different slope efficiency will produce incorrect TX power readings if the calibration constants are wrong. This is not a benign inaccuracy — network management systems use TX/RX power readings to detect degradation and predict failures. Wrong calibration values mean wrong alarms (or missing alarms).

A properly programmed compatible module uses identity fields that identify it correctly to the NOS while leaving the optical calibration constants matched to its actual hardware. The result is accurate diagnostic monitoring and correct NOS acceptance without the serial number collision and false calibration problems that cloning creates.

The EEPROM is not a secret decoder ring that makes a module "pretend" to be something it isn't. It's a mandatory identity document that the NOS uses to make access control and inventory decisions. Customizing it for the target platform is legitimate engineering, not deception.
