Bird
0
0

You created an overlay network but containers on different nodes cannot communicate. What is a likely cause?

medium📝 Troubleshoot Q6 of 15
Docker - Swarm
You created an overlay network but containers on different nodes cannot communicate. What is a likely cause?
AFirewall blocking UDP ports 4789 and 7946 between nodes.
BContainers are using the bridge network instead of overlay.
CDocker daemon is not running on the manager node.
DOverlay networks do not support cross-node communication.
Step-by-Step Solution
Solution:

  1. Step 1: Identify network communication requirements for overlay

    Overlay networks use UDP ports 4789 (VXLAN) and 7946 (control) which must be open.

  2. Step 2: Analyze options

    Firewall blocking UDP ports 4789 and 7946 between nodes. correctly identifies firewall blocking as cause. Containers are using the bridge network instead of overlay. is unrelated if overlay network is created. Docker daemon is not running on the manager node. affects manager but not necessarily communication. Overlay networks do not support cross-node communication. is false.

  3. Final Answer:

    Firewall blocking UDP ports 4789 and 7946 between nodes. -> Option A

  4. Quick Check:

    Open UDP 4789 & 7946 for overlay communication [OK]
Quick Trick: Open UDP ports 4789 and 7946 for overlay networks [OK]
Common Mistakes:
  • Ignoring firewall rules
  • Assuming overlay doesn't need open ports
  • Confusing bridge network with overlay

Want More Practice?

15+ quiz questions · All difficulty levels · Free

Free Signup - Practice All Questions
More Docker Quizzes
Docker Security - Security benchmarks (CIS Docker) - Quiz 2easy Docker Security - Security benchmarks (CIS Docker) - Quiz 4medium Docker in CI/CD - Pushing images from CI - Quiz 1easy Docker in CI/CD - GitLab CI with Docker - Quiz 14medium Image Optimization - BuildKit for improved builds - Quiz 1easy Logging and Monitoring - Alert setup for container health - Quiz 7medium Production Patterns - Canary deployment pattern - Quiz 7medium Resource Management - Why resource limits matter - Quiz 6medium Resource Management - Why resource limits matter - Quiz 15hard Resource Management - Why resource limits matter - Quiz 2easy