Network Troubleshooting Tools for AWS SysOps Administrator Associate
Why Network Troubleshooting Tools Are Important
Network troubleshooting tools are essential for AWS SysOps Administrators because they enable you to diagnose connectivity issues, identify performance bottlenecks, and ensure reliable communication between AWS resources. In production environments, network problems can cause service outages, degraded performance, and security vulnerabilities. Mastering these tools helps you maintain high availability and quickly resolve issues.
What Are Network Troubleshooting Tools in AWS?
AWS provides several native and integrated tools for network troubleshooting:
VPC Flow Logs - Capture information about IP traffic going to and from network interfaces in your VPC. Flow logs can be published to CloudWatch Logs, S3, or Kinesis Data Firehose.
VPC Reachability Analyzer - A configuration analysis tool that enables you to perform connectivity testing between a source and destination in your VPCs. It analyzes all possible paths and identifies blocking configuration issues.
AWS Network Manager - Provides a central dashboard to manage and monitor your global network across AWS and on-premises resources.
Traffic Mirroring - Copies network traffic from elastic network interfaces and sends it to security and monitoring appliances for deep packet inspection.
CloudWatch Metrics - Monitor network-related metrics such as NetworkIn, NetworkOut, and NetworkPacketsIn for EC2 instances.
How These Tools Work
VPC Flow Logs:
- Capture metadata about network traffic (source IP, destination IP, ports, protocol, action taken)
- Can be created at VPC, subnet, or ENI level
- Logs accepted, rejected, or all traffic
- Does not capture packet payloads
- Typical use: identifying blocked connections due to security groups or NACLs
VPC Reachability Analyzer:
- Performs hop-by-hop analysis of network paths
- Checks security groups, NACLs, route tables, and other configurations
- Provides explanations when paths are blocked
- No actual traffic is sent during analysis
- Useful for validating network configurations before deployment
Traffic Mirroring:
- Creates a copy of network traffic
- Requires a mirror source, filter, and target
- Target can be a network load balancer or ENI
- Supports filtering by protocol, port, and direction
Common Troubleshooting Scenarios
1. Instance cannot reach the internet - Check route tables for internet gateway route, verify security groups allow outbound traffic, confirm NACL rules, ensure public IP or NAT gateway is configured
2. Instances in different subnets cannot communicate - Use Reachability Analyzer to identify blocking configurations, review security groups and NACLs on both subnets
3. Intermittent connectivity issues - Enable VPC Flow Logs to capture traffic patterns, analyze rejected traffic entries, correlate with CloudWatch metrics
4. Security investigation - Use Traffic Mirroring for deep packet inspection, analyze Flow Logs for suspicious patterns
Exam Tips: Answering Questions on Network Troubleshooting Tools
1. VPC Flow Logs vs Reachability Analyzer: Flow Logs capture actual traffic data over time, while Reachability Analyzer tests configuration paths and does not require actual traffic. Choose Flow Logs for historical analysis and Reachability Analyzer for configuration validation.
2. Remember Flow Log Limitations: Flow Logs do not capture DNS traffic to Route 53, DHCP traffic, metadata traffic to 169.254.169.254, or traffic to the default VPC router.
3. Security Group vs NACL Issues: If Flow Logs show traffic as REJECT, the issue is likely with NACLs (stateless). Security group denials may not always appear as explicit rejects in Flow Logs.
4. Cost Considerations: Questions may present scenarios where cost-effective solutions are needed. VPC Flow Logs to S3 are more cost-effective than CloudWatch Logs for long-term storage.
5. Traffic Mirroring Use Cases: When questions mention content inspection, threat detection, or deep packet analysis, Traffic Mirroring is typically the correct answer.
6. Reachability Analyzer for Pre-deployment: For questions about validating network paths before launching resources or after configuration changes, Reachability Analyzer is the appropriate tool.
7. Aggregation Intervals: Flow Logs have a default aggregation interval of 10 minutes but can be set to 1 minute for more granular data at additional cost.
8. Cross-Account Analysis: Remember that Reachability Analyzer works within a single AWS account and Region. For cross-account scenarios, consider other approaches.