How do I troubleshoot cloud network issues in AWS, Azure, and GCP?

Troubleshooting cloud network issues requires a solid understanding of cloud-specific components such as VPC peering, route tables, and network ACLs. In this blog, we walk through practical steps to diagnose and resolve connectivity problems in AWS, Azure, and Google Cloud (GCP). Learn how to identify route mismatches, misconfigured security groups, and peering conflicts with real-world scenarios and actionable solutions.

Jul 28, 2025 - 11:53

Updated: 1 month ago

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How do I troubleshoot cloud network issues in AWS, Azure, and GCP?

Quick answer: Start with the basics: check route tables, then VPC peering or VNet links, then security groups and network ACLs, since one wrong rule can block traffic. Next, read cloud flow logs to see what was accepted or rejected, and use each provider's connectivity tools to test paths. Document a checklist so you can repeat the process quickly.

Key takeaways

Check route tables first, then peering, security groups and network ACLs.
Read flow logs to see which packets were accepted or dropped.
Security groups are stateful but network ACLs are not.

What Are Cloud Network Issues and Why Are They Complex?
Why Do VPC Peering and Route Tables Matter?
How to Identify Cloud Route Table Misconfigurations?
What Are Network ACLs and How Can They Block Traffic?
How to Debug Connectivity Issues Using Cloud Logs?
What Are the Tools to Troubleshoot AWS Networking?
What About Azure and GCP Networking Troubleshooting?
Real-World Scenario: AWS VPC Peering + Route Table Misconfiguration
How to Avoid Common Cloud Networking Pitfalls?
Cloud Troubleshooting Checklist
Conclusion

What Are Cloud Network Issues and Why Are They Complex?

Cloud networking in platforms like AWS, Azure, and Google Cloud Platform (GCP) involves complex configurations, Virtual Private Clouds (VPCs), route tables, security groups, and access control lists (ACLs). When misconfigured, even a single routing rule or firewall setting can cause large-scale connectivity issues.

Troubleshooting cloud networks is fundamentally different from traditional on-premises networking. The virtualized and abstracted nature of cloud infrastructure makes visibility and debugging more difficult without the right tools and understanding.

How do I troubleshoot cloud network issues in AWS, Azure, and GCP?

Why Do VPC Peering and Route Tables Matter?

VPC Peering allows two VPCs to communicate with each other. However, successful peering doesn't guarantee traffic flow, route tables must be properly configured on both ends.

For example, in AWS:

Peering is set, but traffic fails.
Route table in VPC A does not have a route to VPC B’s CIDR block.
Adding that route solves the issue.

This scenario is very common and occurs across all cloud providers in some variation.

How to Identify Cloud Route Table Misconfigurations?

Misconfigured route tables often cause issues like:

Services can't talk across VPCs
Inter-region communication fails
Internet access issues even with a NAT Gateway

Example from AWS:

Issue	Possible Cause	Fix
EC2 can't access S3	No route to S3 endpoint in route table	Add VPC endpoint route
VPC Peering not working	Missing route in one VPC's route table	Add route to peer CIDR in both route tables
No internet on private subnet	NAT Gateway missing from route table	Point 0.0.0.0/0 to NAT Gateway

What Are Network ACLs and How Can They Block Traffic?

Network Access Control Lists (ACLs) are stateless filters applied at the subnet level in AWS and Azure. Unlike security groups (which are stateful), ACLs require both inbound and outbound rules to allow return traffic.

Common Mistakes:

Deny rules overriding allow rules
Forgetting to allow ephemeral ports in return path
Applying overly restrictive ACLs for internal traffic

How to Debug Connectivity Issues Using Cloud Logs?

Cloud-native logging is a powerful feature that simplifies troubleshooting:

AWS VPC Flow Logs: Capture IP-level traffic between interfaces
Azure NSG Flow Logs: Show traffic allowed/denied at the NSG level
GCP VPC Flow Logs: Available via Stackdriver Logging

Tip: Enable logging on all VPCs and subnets to capture blocked packets or missing routes.

What Are the Tools to Troubleshoot AWS Networking?

AWS:

VPC Reachability Analyzer: Simulates path and shows where traffic fails.
Flow Logs: Network-level visibility.
CloudWatch Insights: View and filter log events in real-time.

What About Azure and GCP Networking Troubleshooting?

Azure:

Network Watcher: Provides IP flow verification, connection troubleshoot, and packet capture.
NSG Flow Logs: Logs traffic patterns for each Network Security Group.
Effective Security Rules: Helps review what NSG or route is blocking the connection.

GCP:

VPC Flow Logs: Integrated with Cloud Logging
Network Intelligence Center: Visualizes network topology and performance metrics.
Connectivity Tests: Checks reachability between two Google Cloud resources.

Real-World Scenario: AWS VPC Peering + Route Table Misconfiguration

A DevOps team set up VPC peering between dev-vpc and prod-vpc.

Dev EC2 couldn't SSH into prod EC2.
Ping failed.
Peering status: Active.
Route table in prod-vpc was missing the route to dev-vpc's CIDR.

Fix:
Added missing route to prod-vpc route table:

Destination: 10.0.1.0/16 -> Target: pcx-xxxxxx

Traffic resumed instantly.

How to Avoid Common Cloud Networking Pitfalls?

Always verify bidirectional route tables after VPC peering
Use security groups and ACLs together properly
For hybrid networks, ensure VPN/BGP tunnels have correct routes
Don’t forget DNS resolution, some VPCs need shared resolvers
Rely on logging and cloud-native tools for visibility

Cloud Troubleshooting Checklist

Component	Checkpoints
VPC Peering	Routes to remote CIDRs in both VPCs, no overlapping CIDRs
Route Tables	Default and custom routes properly defined, especially for NAT and endpoints
Security Groups	Allow correct ports, both inbound and outbound
Network ACLs	Stateless, must allow return traffic on both sides
Flow Logs	Enable for monitoring and analyzing traffic
Diagnostic Tools	Use AWS Reachability Analyzer, Azure Network Watcher, GCP Connectivity Tests

Conclusion

Cloud networking issues in AWS, Azure, and GCP can become complex fast, especially when dealing with VPC peering, misconfigured route tables, or restrictive ACLs. However, with the right mindset, understanding of virtual networking components, and tools like flow logs and reachability analyzers, you can quickly pinpoint and resolve these problems.

DevOps engineers and cloud architects need cloud network troubleshooting skills to build reliable, scalable, and secure infrastructure.

To take this further with guided labs and an instructor, see our AWS advanced networking training.

Reference

For the authoritative details, see AWS documentation.

Frequently Asked Questions

Common causes include misconfigured route tables, overlapping CIDR blocks in VPC peering, missing security group rules, and ACL conflicts.

VPC peering connects two networks, but if routes aren’t added correctly, communication between them will fail.

AWS VPC Flow Logs, CloudWatch, and Reachability Analyzer are essential tools.

Yes, but some cloud providers restrict ICMP traffic unless explicitly allowed in firewall or security group settings.

A route table defines how traffic is directed within the virtual network and toward other networks or gateways.

Use Azure Network Watcher’s Connection Monitor and Network Performance Monitor to assess latency.

GCP uses firewall rules instead of traditional security groups to allow or deny traffic.

Check Network ACLs on the subnet level and ensure rules allow the required ports and protocols in both directions.

The peering will be established, but traffic won’t route properly between overlapping subnets.

Yes, all three platforms offer tools: AWS has VPC Flow Logs, Azure uses NSG Flow Logs, and GCP provides VPC Flow Logs via Stackdriver.

Check if the internal DNS resolver is working, and ensure correct DNS records are configured in private zones.

Security groups are stateful and apply at the instance level, while ACLs are stateless and apply at the subnet level.

Use the Reachability Analyzer to simulate traffic and test connectivity paths.

Traffic doesn't reach its destination even though instances are up and firewall rules are open.

Azure Network Watcher provides packet capture, IP flow verify, and diagnostic tools.

Yes, GCP allows custom route creation for advanced networking use cases.

To allow instances in private subnets to access the internet without exposing them to incoming traffic.

Ensure VPC peering or VPN/Transit Gateway is correctly configured and supported across regions.

Causes include long routing paths, overloaded interfaces, or resource contention on virtual routers.

Enable flow logs and analyze logs using native cloud monitoring or third-party SIEM tools.

Check security group logs, route propagation, and service quotas for bandwidth or connection limits.

Not directly on cloud routers, but it can be used inside instances to capture traffic if permissions allow.

A tool that simulates and tests network reachability between AWS resources.

Yes, NSGs can filter internal subnet-to-subnet traffic based on defined rules.

It denies all incoming traffic and allows all outbound unless explicitly modified.

Use flow logs and traceroute tools to see if traffic returns via a different path.

Check security groups, ACLs, firewall rules, and route tables to ensure traffic is permitted.

Yes, they are distributed, cloud-native, and often integrated with IAM and service-based rules.

Use billing dashboards and enable VPC flow logging to identify high-cost communication.

Yes, if explicitly allowed in the security group or firewall rule.

Enable VPC Flow Logs (AWS/GCP), NSG Flow Logs (Azure), and monitor DNS resolution logs.

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Vaishnavi

Vaishnavi is a skilled tech professional at the Ethical Hacking Training Institute in Pune, responsible for managing and optimizing the technical infrastructure that supports advanced cybersecurity education. With deep expertise in network security, backend operations, and system performance, she ensures that practical labs, online modules, and assessments run smoothly and securely. Her behind-the-scenes contributions play a vital role in delivering a seamless and secure learning experience for aspiring ethical hackers.