Introduction
Nutanix Flow delivers enterprise-grade security and advanced network virtualization within Nutanix AHV clusters. With both Flow Network Security (microsegmentation/firewall) and Flow Networking (overlay/SDN), organizations can implement policy-driven segmentation, network overlays, and fine-grained traffic control. When network or security issues arise, knowing how to efficiently diagnose and resolve problems is essential for maintaining uptime and compliance.
This in-depth guide walks you through the top tools, log locations, and step-by-step troubleshooting workflows—all illustrated with real-world incident examples. Whether you’re an architect, network engineer, or infrastructure engineer, you’ll find actionable methods and command references tailored for rapid incident response.
1. Nutanix Flow Architecture: What You’re Troubleshooting
Before diving into diagnostics, let’s quickly recap Flow’s architecture:
- Flow Network Security: Distributed firewall, policy enforcement, service chains (IDS/IPS, traffic inspection).
- Flow Networking: SDN controller, managed network overlays (VPCs, routers, load balancers), network automation.
Key troubleshooting entry points:
- Prism Central: Central UI for policy/rule review, log access, and network visualization.
- CLI/API: Fine-grained inspection, command-driven troubleshooting, log extraction.
2. Common Troubleshooting Scenarios
Let’s explore frequent issues you may encounter:
Scenario A: VM-to-VM Traffic Blocked
Symptoms:
- Application unreachable between VMs on same subnet or across subnets
- Ping/SSH fails, app connections timeout
Initial Steps:
- Policy Review in Prism Central
- Go to Prism Central → Security → Network Policies
- Filter by source/destination VM(s)
- Check for explicit DENY or missing ALLOW rule
- VM Tag/Category Verification
- Ensure both VMs have expected categories/tags for policy application
CLI Checks:
# Show VM flow security state
acli vm.nic.list <VM-Name>
# Show firewall rules applied to a VM
ncli flowvm get name=<VM-Name>
Common Causes:
- Missing/incorrect policy assignment
- Incorrect VM category mapping
- Implicit DENY at end of rule stack
Official Reference:
Nutanix Flow Security Troubleshooting Guide
Scenario B: Misapplied Rules After Policy Change
Symptoms:
- Policy or rule changed, but traffic still not flowing as expected
- Firewall rule hits are not incrementing
Diagnostic Steps:
- Force Policy Refresh:
- In Prism Central, manually refresh Flow rules or restart Prism Central service if needed.
- Check Rule Status:
- Confirm rule status (active, pending, error) in Prism Central UI.
CLI/API:
# List all current policies
ncli flow-policy list
# Check status of rules deployment
ncli flow-rule list
- Review Controller Health:
- Verify SDN/Controller VMs are healthy in Prism Central → Health dashboard
Typical Root Causes:
- Policy engine desync due to network events or maintenance
- Stale VM metadata (tags/categories)
- Prism Central service lag
Official Reference:
Nutanix Flow FAQ and Troubleshooting
Scenario C: Performance Issues – High Latency or Packet Loss
Symptoms:
- Apps report high latency, intermittent connectivity
- TCP retransmits, slow application response
Workflow:
- Baseline Network Performance
- Use Prism Central → Network Visualization for overlay path analysis
- Use Nutanix X-Ray (if available) for synthetic tests
- Overlay vs. Underlay Isolation
- Confirm if latency is within overlay network (Flow Networking), or base physical network
- Logs to Check
- CVM logs:
/home/nutanix/data/logs/flow_proxy.out less /home/nutanix/data/logs/flow_monitor.out - Flow Controller logs (Prism Central Controller VM):
/var/log/flow_controller.log - Hypervisor logs:
/var/log/vmkernel.log (ESXi) journalctl -u flow-agent (AHV)
- CVM logs:
- Rule Hit Counters
- Check which rules are seeing traffic using Prism Central
- Look for “zero-hit” rules that might be shadowing or blocking
CLI Quick Check:
# Show Flow networking and controller health
ncli flow-network list
# List Flow agent state per host
ncli host list | grep flow
Root Causes:
- Overlay network congestion or misconfiguration
- Hypervisor resource bottleneck
- Flow agent/controller health issue
Official Reference:
Nutanix Flow Networking Troubleshooting
3. Master Tools for Nutanix Flow Troubleshooting
A. Prism Central
- Policy and rule management
- Real-time traffic visualization
- Health dashboards
- Integrated event/log search
B. Command Line/SSH
- ncli, acli, and OS-level commands for state review and log scraping
C. API & PowerShell
- Automate checks and pull configuration/rule snapshots
- Nutanix REST API Explorer
D. Flow Logs
- Located on Controller VMs and CVMs
- Rotating logs with historic and real-time entries
- Use grep for incident correlation
E. Third-Party Tools
- Wireshark: Overlay/underlay packet analysis
- X-Ray: Automated testing and validation
4. Proactive Practices and Tips
- Always baseline healthy network behavior after new policies or upgrades.
- Schedule regular exports of Flow rules/policies using API for DR and audit.
- Leverage categories/tags consistently across VM lifecycles to prevent shadowing and misapplied rules.
- Document incident root causes and maintain a playbook of common commands and workflows.
5. Sample Command Cheat Sheet
| Task | Command / Path |
|---|---|
| List all Flow policies | ncli flow-policy list |
| Get Flow status for a VM | ncli flowvm get name=<VM-Name> |
| Show Flow agent status on all hosts | `ncli host list |
| View Flow proxy log (CVM) | /home/nutanix/data/logs/flow_proxy.out |
| Show rules applied via Prism Central | Prism Central → Security → Network Policies |
| Policy state via API | Use REST API /api/nutanix/v3/flow_policies/list |
6. References and Further Reading
- Nutanix Flow Security Troubleshooting Guide
- Nutanix Flow Networking Troubleshooting
- Nutanix REST API Explorer
- Nutanix Community Blog: Top 10 Flow Troubleshooting Tips
Conclusion
Troubleshooting Nutanix Flow is about combining structured diagnostic steps, deep log analysis, and scenario-based playbooks. By understanding both the Flow Network Security and Networking layers, and utilizing the right mix of GUI, CLI, and API tools, architects and engineers can resolve issues quickly and confidently.
Disclaimer: The views expressed in this article are those of the author and do not represent the opinions of Nutanix, my employer or any affiliated organization. Always refer to the official Nutanix documentation before production deployment.
Executive Summary The modern enterprise faces evolving security threats that demand both granular segmentation and robust perimeter defense. Nutanix Flow enables policy-driven...