---
title: "Pre-Deployment Checklist for 800G OSFP in Spine-Leaf Fabrics"
type: tutorial
target_audience: technical
score: 9/10
---

First 800G OSFP spine-leaf deployments fail in predictable ways, and almost all of the failure modes were already documented in TAC cases, vendor release notes, and network operator incident reports before the team doing the deployment encountered them. The engineers who spent 36 hours troubleshooting an 800G spine that would not bring up its OSFP ports had a 99 percent chance of encountering a firmware compatibility issue that was fixed in a release published three months before their deployment date. This pre-deployment checklist is the operational synthesis of those documented failure modes, structured to be run before the first module is inserted into a production chassis.

Firmware version verification is the first and most consequential check. Both Arista EOS and Cisco NX-OS had 800G OSFP support introduced in releases that contained known defects specific to OSFP port bring-up and DOM reporting that were fixed in subsequent releases. On Arista EOS, initial 800G OSFP support arrived in EOS 4.30.0, which supported 800GBASE-DR8 and SR8 optics with working link negotiation. EOS 4.30.1 fixed a bug where OSFP modules in specific slot positions of the 7800R3 series chassis reported incorrect cage temperature values that could cause the thermal protection system to incorrectly mask or disable ports. EOS 4.30.3 addressed a DOM polling race condition that caused CMIS state machine failures on OSFP modules at system boot when multiple OSFP ports initialized simultaneously. Deploying on EOS 4.30.0 means running with all three of these defects active. The correct target version for initial 800G OSFP deployments on Arista 7800 series as of mid-2026 is EOS 4.31.2 or later.

On Cisco NX-OS, 800G OSFP support for Nexus 9000 series platforms with the appropriate line cards appeared in NX-OS 10.3(2)F, which addressed the initial CMIS compatibility issues encountered with first-generation OSFP modules. NX-OS 10.4(1)F improved OSFP DOM polling to correctly handle the longer initialization time of 800G OSFP modules — which require approximately 3 to 5 seconds to complete the CMIS state machine initialization versus 1 to 2 seconds for QSFP-DD — preventing the platform from incorrectly declaring the module absent during boot. Before NX-OS 10.4(1)F, OSFP modules in specific line card slot positions would initialize correctly on cold boot but fail to reinitialize after a line card OIR event, requiring a manual `shut/no shut` on each affected port. The correct target NX-OS version for production 800G OSFP as of mid-2026 is 10.4(2)F or later.

EEPROM validation is the second checklist item and covers two distinct aspects. The first is platform compatibility — verifying that the module's EEPROM presents the vendor ID, part number, and CMIS revision that the target platform expects for unsuppressed operation. OSFP modules use CMIS (Common Management Interface Specification) version 4.0 or 5.0 for module management, and some platform-specific implementations have requirements about which CMIS revision a module must advertise. A module advertising CMIS 3.0 may initialize correctly on some platforms but fail to expose the full register set that 800G management functions require. Flexoptix EEPROM programming can address platform-compatibility encoding and CMIS revision presentation for OSFP modules, ensuring the module presents correctly across the specific platform versions in the target deployment.

The second EEPROM validation aspect is per-lane capability advertisement. OSFP modules at 800G implement media-side application codes that identify the supported 800G variants — 800GBASE-SR8, DR8, FR8, or 2xFR4 breakout. The application code must match the physical module variant, and the host system uses the application code to configure the SerDes lane mapping and FEC configuration. A mismatch between the application code and the physical module — which can result from incorrect EEPROM programming or from receiving a module that was mislabeled at the manufacturing stage — produces a link that initializes the host-side SerDes correctly but applies the wrong FEC configuration to the media-side lanes, generating uncorrectable FEC errors from the first transmitted frame.

DOM baseline capture is the third checklist item. After EEPROM validation and with the chassis running the verified firmware version, insert the module into a test chassis under representative thermal load and capture the following values within 30 minutes of thermal steady state: TX power per lane (8 lanes for 800G), RX power per lane (8 lanes), TX bias current per lane, module die temperature, supply voltage (3.3V primary), and all configured alarm and warning thresholds. This baseline data goes into the CMDB alongside the module serial number, target chassis position, and fiber path identifier. For 800G SR8 modules on OM4 or OM5, note the per-lane TX launch power variance — it should be less than 1.5 dB across all eight lanes for a healthy module. Lane imbalance above 2 dB at commissioning indicates a factory defect and the module should be returned before production deployment.

Alarm configuration is the fourth item and requires setting thresholds that are specific to the deployment context rather than accepting the factory defaults. Factory alarm thresholds for OSFP modules are set conservatively to avoid false positives across all deployment scenarios. For a production deployment where the power budget is known and the fiber path is characterized, alarm thresholds tuned to the specific deployment provide earlier warning of degradation. A practical configuration sets TX power low warning at 0.5 dB above the receiver sensitivity floor on the far end module (not at the generic factory threshold), TX bias current high warning at 75 percent of the rated maximum (rather than 90 percent), and cage temperature high warning at 60°C (rather than the specification maximum of 70°C). These tighter thresholds generate alerts at a point where the module is degrading toward a failure condition, providing time to schedule a replacement during a maintenance window.

The 48-hour burn-in process is the fifth item and is operationally more important for first 800G deployments than it was for mature 100G or 400G deployments because the 800G installed base is young enough that early-life failure rates are not yet fully characterized. Burn-in consists of running the module at full-rate traffic for 48 continuous hours while polling DOM registers every 60 seconds and monitoring pre-FEC BER on each lane. Modules that fail the burn-in period — defined as pre-FEC BER exceeding 1e-4 on any lane for more than 5 continuous minutes — are returned before going into production. Industry data on infant mortality in optical transceivers consistently shows that a 24 to 48-hour burn-in period catches 60 to 75 percent of the modules that would otherwise fail within the first 90 days of production service, at the cost of the burn-in time rather than the cost of a production outage.

Common mistakes on first 800G deployments fall into three categories that repeat across operator environments. The first is underestimating the time to thermal steady state — OSFP modules at 800G require 20 to 35 minutes from cold insertion to reach thermal equilibrium in a production chassis, and DOM readings taken before steady state produce misleading baselines. The second is treating 800G DAC cables as interchangeable with 400G DAC cables — the physical OSFP connector on an 800G cable is different from the QSFP-DD connector on a 400G cable, and mislabeled or misidentified cable inventory from mixed deployments causes the kind of connection confusion that generates multi-hour troubleshooting when a cable is physically inserted but the switch reports no module present. The third is not reading the OSFP module initialization sequence in the chassis event log before declaring a port failed — the CMIS state machine for 800G OSFP produces a specific sequence of syslog messages during successful initialization, and any deviation from that sequence points directly to the failure stage in the initialization process, reducing root cause analysis time from hours to minutes.
