Applies to: Accessible copper Ethernet path. Read-only observations and supported cable/port comparisons; no network configuration reset or powered probing.
- Signal path
- Computer Ethernet port → Documented patch cable / wall link / any injector → Switch Ethernet data port
What the path requires
- Save work and identify managed equipment before moving a connection. Stop for damaged plugs/jacket, unusual heat, unknown passive power injection or a policy restriction.
Worked documentary examples
Worked documentary path
Documented outcome: Documentary path: a workstation has no link through wall patching. The same enabled ports link through a suitable short direct cord. This narrows the enquiry to the removed wall/patch path; it does not certify the short cable or identify a failed punchdown.
Alternative or unknown branch
Documented outcome: If neither port's capability/status is available, record that missing evidence and request the model's port/LED table; do not infer failure from connector color.
Follow the observation
Read the result before moving to the next branch. Leave unavailable evidence unknown.
1. One end is labelled Console or its manual describes RS232.
Check: Read the exact port labels and manuals at both ends.
What it supports: The RJ45 shape is being used for a different interface.
Next action: Use a documented Ethernet port for networking; use the separate serial-console package only for authorized administration.
Stop / escalation: Stop for electrical damage, unknown power injection, inaccessible installed wiring or managed-port restrictions. No contact probing, termination work or configuration resets.
2. Either device is off or the indicated port is administratively disabled/error-disabled.
Check: Record the port indicators at both ends and check power.
What it supports: A powered and enabled link partner has not been established.
Next action: Use the model's indicator/status table; ask its administrator to investigate the reported state. Do not reset or re-enable it through this guide.
Stop / escalation: Stop for electrical damage, unknown power injection, inaccessible installed wiring or managed-port restrictions. No contact probing, termination work or configuration resets.
3. Direct link appears, but the original wall/patch path does not link.
Check: Where the manuals permit it, compare one suitable known-working short direct cable on the same enabled ports.
What it supports: The difference is in the removed path; it does not identify which jack, patch cord or installed segment is faulty.
Next action: Label the two paths and have the cabling maintainer wiremap/qualify the original channel.
Stop / escalation: Stop for electrical damage, unknown power injection, inaccessible installed wiring or managed-port restrictions. No contact probing, termination work or configuration resets.
4. No link even on the supported direct comparison.
Check: Keep the short comparison and inspect the two port capabilities.
What it supports: Cable replacement alone has not resolved port, adapter or endpoint limitations.
Next action: Collect exact device/adapter model, OS/firmware, port status and cable identity for the endpoint vendor; a single lit LED is not proof of a functional bidirectional path.
Stop / escalation: Stop for electrical damage, unknown power injection, inaccessible installed wiring or managed-port restrictions. No contact probing, termination work or configuration resets.
5. Both ends report a stable link.
Check: Check the link observation after a controlled comparison.
What it supports: A physical link is established; address, VLAN, authentication and upstream routing are separate.
Next action: If Internet access still fails, preserve the cable result and use the organization's network-connectivity procedure.
Stop / escalation: Stop for electrical damage, unknown power injection, inaccessible installed wiring or managed-port restrictions. No contact probing, termination work or configuration resets.
Your next useful observation
If Internet access still fails, preserve the cable result and use the organization's network-connectivity procedure.
Keep these limits
- Stop for electrical damage, unknown power injection, inaccessible installed wiring or managed-port restrictions. No contact probing, termination work or configuration resets.
- Source-documented decision path; no link test performed.
Source documents, revisions and inspection methods
Configure and Verify Ethernet 10/100/1000Mb Half/Full Duplex Auto-Negotiation
Cisco · Document 10561, updated 2025-11-06
When to Use 10/100 and 1000Mb Auto-Negotiation; Appendix D interface fields
Inspected 2026-10-23 by public_page. AI primary-source text inspection; not independent human review or hardware measurement
Observation/negotiation interpretation for documented Cisco context. No live configuration, reset or erase instructed.
Read the original sourceCatalyst3650 Hardware Installation Guide — Troubleshooting
Cisco · Updated2014-07-18
Bad or Damaged Cable; Ethernet and Fiber Cables; Link Status; SFP Modules; Speed/Duplex
Inspected 2026-10-23 by public_page. AI primary-source text inspection; no hardware test
Documented observation and controlled comparison for a named platform; reset/configuration/driver-change procedures are not carried into this lesson.
Read the original sourceSource-documented education. Hardware behavior and independent human review have not been performed for these examples.