Reference Architecture: Cabling Standards
Purpose: For platform engineers, provides cable types, structured cabling standards, and documentation requirements.
Overview
Cabling errors are the most common cause of network outages in data centers. This document defines cable types, labeling, routing, and documentation standards for openCenter deployments. Follow these standards to reduce troubleshooting time and prevent accidental disconnections.
Cable Types
Data Cables
| Cable Type | Speed | Max Distance | Use Case |
|---|---|---|---|
| DAC SFP28 (25 GbE Twinax) | 25 Gbps | 5 m | Server to ToR switch (intra-rack) |
| DAC QSFP28 (100 GbE Twinax) | 100 Gbps | 5 m | Leaf to spine (same rack or adjacent) |
| AOC SFP28 (25 GbE Active Optical) | 25 Gbps | 10–30 m | Server to switch (inter-rack) |
| AOC QSFP28 (100 GbE Active Optical) | 100 Gbps | 10–100 m | Leaf to spine (inter-rack) |
| OM4 MMF LC-LC (Multimode Fiber) | 100 Gbps | 150 m | Inter-rack backbone |
| OS2 SMF LC-LC (Single-mode Fiber) | 100 Gbps+ | 10 km | Inter-building or long runs |
| Cat6A RJ45 | 10 Gbps | 100 m | OOB management (BMC/IPMI) |
| Cat6 RJ45 | 1 Gbps | 100 m | OOB management (legacy) |
Power Cables
| Cable Type | Use Case |
|---|---|
| IEC C13–C14 (10A) | Servers, switches |
| IEC C19–C20 (16A) | High-power servers, UPS connections |
Use color-coded power cables to distinguish Feed A (red) from Feed B (blue). This prevents accidental disconnection of the wrong power feed during maintenance.
Cable Selection Guide
| Connection | Recommended Cable | Alternative |
|---|---|---|
| Server NIC → ToR Switch (same rack) | 25 GbE DAC SFP28, 3 m | 25 GbE AOC SFP28 |
| ToR Leaf → Spine (same row, < 5 m) | 100 GbE DAC QSFP28, 3 m | 100 GbE AOC QSFP28 |
| ToR Leaf → Spine (inter-row, 5–30 m) | 100 GbE AOC QSFP28 | OM4 MMF + QSFP28 transceivers |
| ToR Leaf → Spine (> 30 m) | OM4 MMF LC-LC + QSFP28 SR4 | OS2 SMF + QSFP28 LR4 |
| BMC/IPMI → OOB Switch | Cat6A RJ45, 3 m | Cat6 RJ45 |
| Server PSU → PDU | C13–C14, 2 m (color-coded) | C19–C20 for high-draw servers |
Prefer DAC cables for intra-rack connections. They are cheaper, lower latency, and lower power than optical alternatives. Switch to AOC or fiber only when distance exceeds 5 m.
Labeling Standards
Every cable must be labeled at both ends. Use machine-printed labels (not handwritten). Labels must be readable without removing the cable.
Label Format
<source_device>:<source_port> → <dest_device>:<dest_port>
Examples
| Source End Label | Destination End Label |
|---|---|
DC1-R01-HV01:NIC0 → DC1-R01-LF01:Eth1/1 | DC1-R01-LF01:Eth1/1 → DC1-R01-HV01:NIC0 |
DC1-R01-HV01:NIC2 → DC1-R01-LF02:Eth1/1 | DC1-R01-LF02:Eth1/1 → DC1-R01-HV01:NIC2 |
DC1-R01-LF01:Eth1/49 → DC1-R01-SP01:Eth1/1 | DC1-R01-SP01:Eth1/1 → DC1-R01-LF01:Eth1/49 |
Label Materials
| Environment | Label Type |
|---|---|
| Standard data center | Self-laminating wrap-around labels (Brady B-427, Panduit S100X150) |
| High-density / fiber | Flag-style labels with clear window |
| Power cables | Color-coded heat-shrink or wrap labels |
Cable Routing
Intra-Rack
- Route data cables through horizontal cable managers between device groups.
- Route power cables along the vertical PDU channel (rear of rack).
- Maintain minimum bend radius: 25 mm for DAC/copper, 30 mm for fiber.
- Do not zip-tie fiber cables tightly — use Velcro straps to avoid micro-bending.
- Separate data and power cables by at least 50 mm to reduce electromagnetic interference.
Inter-Rack
- Use overhead cable trays or under-floor pathways.
- Group cables by function: data in one tray, fiber in another, power in conduit.
- Leave 25% spare capacity in cable trays for future growth.
- Fiber runs must use innerduct or fiber raceway to protect against physical damage.
- Label both ends of every inter-rack cable and record the run in the cable database.
Structured Cabling Compliance
Follow TIA-942 (Telecommunications Infrastructure Standard for Data Centers) or equivalent local standard:
| Requirement | Standard |
|---|---|
| Horizontal cabling | TIA-568.2-D (copper), TIA-568.3-D (fiber) |
| Patch panel termination | TIA-568 T568B wiring (for RJ45) |
| Fiber connector | LC duplex (preferred), MPO/MTP for trunk cables |
| Bend radius | Per cable manufacturer spec (minimum) |
| Pull tension | Per cable manufacturer spec (maximum) |
| Testing | Certify all copper runs with a cable certifier (Fluke DSX-8000 or equivalent) |
Documentation Requirements
Maintain a cable database (spreadsheet, DCIM tool, or NetBox) with the following fields for every cable:
| Field | Example |
|---|---|
| Cable ID | DC1-R01-C001 |
| Source Device | DC1-R01-HV01 |
| Source Port | NIC0 |
| Destination Device | DC1-R01-LF01 |
| Destination Port | Eth1/1 |
| Cable Type | 25 GbE DAC SFP28 |
| Length | 3 m |
| Color | Black (data) / Red (power A) / Blue (power B) |
| Install Date | 2025-01-15 |
| VLAN/Purpose | Management + VM Network (bond0) |
Update this database whenever cables are added, moved, or removed. Stale documentation is worse than no documentation — it causes incorrect troubleshooting.
Spare Cable Inventory
Keep spares on-site for emergency replacement:
| Cable Type | Quantity | Lengths |
|---|---|---|
| 25 GbE DAC SFP28 | 4 | 2× 3 m, 2× 5 m |
| 100 GbE DAC QSFP28 | 2 | 2× 3 m |
| Cat6A RJ45 | 4 | 2× 2 m, 2× 5 m |
| C13–C14 Power (red) | 2 | 2 m |
| C13–C14 Power (blue) | 2 | 2 m |
| OM4 LC-LC Fiber | 2 | 10 m |
Considerations
- Transceiver compatibility: Use switch-vendor-branded or certified third-party transceivers. Uncertified optics may trigger warnings or be disabled by switch firmware.
- Fiber cleaning: Clean all fiber connectors with a one-click cleaner before every insertion. A single dust particle on an LC connector causes signal loss.
- Cable management arms: If servers have cable management arms, account for the additional depth when selecting rack depth and cable lengths.
- Decommissioning: When removing equipment, remove all associated cables. Abandoned cables ("cable spaghetti") obstruct airflow and make future work harder.
- Audit schedule: Walk the racks quarterly to verify labels match the cable database and no unauthorized cables have been added.