Work out why three hybrid links are down

short · 35 min · Objective 1.3

Task

Diagnose three connectivity failures from their symptoms. Each is a real and common cause, and each has a distinguishing signature that separates it from the others.

Steps

  1. Write the three symptoms into lab/links.md: (a) the tunnel never establishes and the device log mentions proposal mismatch; (b) the tunnel reports UP and no traffic passes; (c) hosts in network A reach network B, and network B cannot reach network C which is peered to B.
  2. For each, name the cause and the exact thing you would check first.
  3. For (b), list the two most likely causes and the single check that distinguishes them.
  4. For (c), state the property of peering responsible and the two ways to resolve it.
  5. Add a fourth case of your own describing a private endpoint whose DNS is not configured, and write what makes it hard to notice.

Verify

grep -Eci 'phase (1|2)|proposal|ike' lab/links.md
grep -Eci 'route (table|propagation)' lab/links.md
grep -Eci 'transitive' lab/links.md
grep -Eci 'public (ip|address)|nat gateway' lab/links.md

All four must be non-zero. The last one is the private-endpoint case, whose whole difficulty is that nothing is broken -- traffic simply takes the expensive path.

This is an independent study companion for CompTIA Cloud+ CV0-004 and is not produced by or endorsed by CompTIA.