The question describes a scenario where a network administrator has already identified a problem (down internet link), confirmed the cause, and implemented a solution (failing over to a backup link). According to standard IT troubleshooting and incident response methodologies, the immediate next step after implementing a corrective action is to verify that the solution has resolved the issue and that the system has returned to a fully functional state. This step is critical to ensure the failover was successful and that users have their services restored before proceeding to the final documentation phase.

A. Document the lessons learned.

This is part of the final phase of the troubleshooting process, which occurs only after the solution has been implemented and full functionality has been verified.

B. Establish a plan of action.

A plan of action—to fail over traffic to the backup link—was already established and executed. This step has already been completed.

C. Identify the problem.

This was the initial step in the process. The administrator identified the problem by examining logs and confirming the link status with the provider.

1. National Institute of Standards and Technology (NIST) Special Publication 800-61 Rev. 2

Computer Security Incident Handling Guide.

Reference: Section 3.3.4

"Recovery."

Content: This section details the recovery phase of incident response. It explicitly states

"After a system is recovered

it should be validated to ensure that it is functioning normally." This directly supports that verification (D) is the step following the implementation of a solution. The subsequent section

3.3.5 "Post-Incident Activity

" discusses "lessons learned" (A)

confirming it as a later step.

2. Mir

N. F. (2014). Computer and Communication Networks (2nd ed.). Pearson.

Reference: Chapter 16

"Network Management

" Section 16.2

"Fault Management."

Content: University courseware and standard textbooks on network management describe a systematic process for fault management. This process includes fault detection

isolation

and correction

which is immediately followed by testing and verification to ensure the correction was successful before closing the trouble ticket.

3. Carnegie Mellon University

Software Engineering Institute. (2016). Defining the Process for Incident Triage.

Reference: Document CMU/SEI-2016-TN-009

Section 3

"A Process for Incident Triage."

Content: This academic publication outlines a formal process for handling network and security incidents. The process flow shows that after a resolution action is taken ("Remediate")

the next required step is to "Verify" the fix before the incident can be considered resolved and documented.