Plan diverse routes and identify shared failure points

What you should be able to do

Trace two proposed fiber paths, identify where one incident could affect both, and describe what evidence would support a limited route-diversity claim. This is a planning lesson, not an instruction to alter or interrupt a live network.

Teaching

Route diversity concerns physically different paths; redundancy concerns additional assets or backup capacity. CISA's published guidance treats these as related but distinct elements of communications resilience. Its guidance also warns that separate providers can use the same lines or facilities. A network diagram with two links therefore needs a corresponding physical-route record.

Define the scope before saying “diverse.” A comparison between two building entrances does not prove independence inside those buildings or throughout a provider network. Identify the service, endpoints, route segments and failure events being assessed. Avoid an unqualified promise that a system cannot fail.

Worked through

The training inventory lists: Path 1: A north entry → north duct → HH-01 → B north entry. Path 2: A south entry → south duct → HH-01 → B south entry.

Different entries do not eliminate HH-01. Mark that location in both records, name the affected services and ask the designer to assess the relevant failure event. Do not count the two duct labels as proof that the paths remain separate between documented points.

A revised proposal replaces the second handhole segment: Path 2 revision: A south entry → south corridor → HH-02 → B south entry. This removes the named common handhole in the drawing. It does not establish that the two corridors avoid the same bridge, flood exposure, construction work zone or downstream facility. Keep those items unresolved until the supporting route evidence exists.

Dependency Exercise

Imagine the two paths terminate on different switch ports but the same switch chassis. A single chassis failure may still interrupt both. Now imagine two chassis powered by the same unprotected supply. The shared power dependency remains. These examples show why a route review and a service-resilience review have different boundaries.

Likewise, two service-provider invoices do not identify the underground route. Request current route or diversity evidence through authorized project channels. This lesson itself sends no provider request. If detailed information cannot be disclosed, record the assurance actually received and its scope instead of inventing a map.

Create A Shared-Point Register

Use one row for each suspected common point:

• Location or asset ID.
• Path 1 evidence and Path 2 evidence.
• Credible event that could affect both.
• Services affected.
• Proposed mitigation or accepted residual risk.
• Responsible reviewer and unresolved questions.
• Drawing revision and evidence date.

Example row: HH-01; shown on drawings A-03 and B-04; damage to the common enclosure; both campus uplinks; assess reroute via HH-02; reviewer not yet assigned; evidence remains a fictional classroom drawing.

Do not assign a universal separation distance. The appropriate arrangement depends on the hazards, site constraints and design requirements. Geographical separation should be evaluated against the event being addressed, not simply measured between lines on a diagram.

Failover Is Another Check

A physically distinct cable path does not prove that networking equipment will detect a failure and restore the required service. The authorized commissioning plan should define which service is observed, the allowed interruption and the restoration behavior to verify. Record what was actually demonstrated. An apprentice should not unplug live fiber or remove power merely to test a classroom hypothesis.

Knowledge Check

Where beginners go wrong

Sources