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

Table of Contents

• 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
• Frequently Asked Questions (FAQs)

What Are Cloud Network Issues and Why Are They Complex?

Cloud networking in platforms like AWS, Azure, and Google Cloud Platform (GCP) involves intricate 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.

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:

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

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.

Whether you're a DevOps engineer or cloud architect, mastering cloud network troubleshooting is essential for building reliable, scalable, and secure infrastructure.

FAQs

What are the common causes of cloud network issues?

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

How does VPC peering affect cloud connectivity?

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

What tools help troubleshoot AWS networking issues?

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

Can I use ping or traceroute in the cloud?

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

What is a route table in cloud networking?

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

How can I diagnose Azure network latency?

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

What is GCP's equivalent of a security group?

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

How do I detect ACL blocking in AWS?

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

What happens if two VPCs have overlapping CIDRs?

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

Is there a way to visualize cloud network traffic?

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

How do I troubleshoot DNS issues in cloud?

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

What is network ACL vs security group?

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

How can I verify VPC peering works in AWS?

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

What are the signs of a broken route table in cloud?

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

How does Azure diagnose network issues?

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

Can I create custom route tables in GCP?

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

What is a NAT Gateway used for?

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

How to fix inter-region communication issues?

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

What causes high latency in cloud networking?

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

How can I audit cloud network traffic?

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

How do I troubleshoot connection drops in cloud?

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

Is Wireshark usable in the cloud?

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

What is AWS Reachability Analyzer?

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

Can Azure NSG block internal traffic?

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

What’s the default behavior of a GCP firewall?

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

How to detect asymmetric routing in cloud?

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

How do I fix “Request Timed Out” in cloud environments?

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

Are cloud firewalls different from traditional firewalls?

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

How to monitor inter-zone traffic costs?

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

Can I use ICMP in AWS/GCP?

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

What logs should I enable for network troubleshooting?

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