Network Visibility & Performance Metrics

This guide covers the critical metrics and tools required to maintain visibility, troubleshoot connectivity, and optimize network performance within the AWS Advanced Networking Specialty (ANS-C01) scope.

Learning Objectives

After studying this guide, you will be able to:

• Identify appropriate metrics (Latency, Throughput, Packet Loss, Jitter) for network health assessment.
• Select the correct AWS tool (VPC Flow Logs, Traffic Mirroring, CloudWatch) for specific visibility requirements.
• Analyze routing patterns and verify connectivity intent using Reachability Analyzer.
• Differentiate between metadata-level logging and deep packet inspection.
• Establish a performance baseline for hybrid and cloud-native architectures.

Key Terms & Glossary

• VPC Flow Logs: A feature that enables you to capture information about the IP traffic going to and from network interfaces in your VPC.
• Traffic Mirroring: An Amazon VPC feature that you can use to copy network traffic from an elastic network interface (ENI) and send it to out-of-band security and monitoring appliances.
• Reachability Analyzer: A configuration analysis tool that enables you to perform static connectivity testing between a source resource and a destination resource in your VPC.
• Jitter: The variation in the delay of received packets, which can negatively impact real-time applications like VOIP or video streaming.
• MTU (Maximum Transmission Unit): The size of the largest protocol data unit that can be communicated in a single network layer transaction (standard is 1500 bytes; Jumbo frames are 9001 bytes).

The "Big Idea"

Network visibility is not just about "is it up?" but "how well is it performing?" In complex AWS environments, visibility requires a layered approach: CloudWatch for high-level health, VPC Flow Logs for connection metadata (who, what, when), and Traffic Mirroring for deep forensic analysis (the actual payload). Together, these tools allow a network engineer to transition from reactive firefighting to proactive optimization.

Formula / Concept Box

Hierarchical Outline

• Core Performance Metrics
  • Latency: Critical for user experience; affected by distance and routing hops.
  • Packet Loss: Often caused by congested buffers or MTU mismatches.
  • Throughput: Impacted by instance type limits and ENA/EFA capabilities.
• AWS Visibility Toolset
  • CloudWatch: Centralized metrics (NetworkIn/Out), logs, and alarms.
  • VPC Flow Logs: Captures source/dest IP, port, protocol, and action (ACCEPT/REJECT).
  • Traffic Mirroring: Full packet capture for deep packet inspection (DPI).
• Verification & Troubleshooting Tools
  • Reachability Analyzer: Checks routing/ACL/Security Group logic without sending packets.
  • Transit Gateway Network Manager: Provides global topology views and cross-region health.
  • Route 53 Query Logging: Monitors DNS resolution patterns and failures.

Visual Anchors

Network Visibility Flow

Visualizing Latency vs. Jitter

Definition-Example Pairs

• Metric: Packet Loss
  • Definition: The percentage of packets that fail to reach their destination.
  • Example: A VPN tunnel showing 10% packet loss during peak hours likely indicates an ISP congestion issue or a MTU/MSS clamping problem.
• Tool: Reachability Analyzer
  • Definition: A static analysis tool that tests reachability between two points in a VPC.
  • Example: You cannot ping an EC2 instance. Reachability Analyzer identifies that the NACL (Network ACL) is blocking outbound traffic on port 443.
• Log: Access Logs
  • Definition: Detailed logs of requests made to load balancers or CloudFront.
  • Example: Using ALV Access Logs to identify the specific client IP addresses causing a surge in 5XX error responses.

Worked Examples

Example 1: Troubleshooting "Connection Refused"

Scenario: An application on Instance A cannot connect to a database on Instance B.

1. Step 1: Check VPC Flow Logs for the relevant ENIs.
2. Step 2: Filter for REJECT. If found, check the Security Group or NACL rules.
3. Step 3: If Flow Logs show ACCEPT but the connection fails, use Reachability Analyzer to verify the path through Route Tables and Gateways.

Example 2: Analyzing Packet Shaping Issues

Scenario: Video streaming performance is degraded despite high bandwidth.

1. Step 1: Enable VPC Traffic Mirroring on the source ENI.
2. Step 2: Route the mirrored traffic to a Wireshark-equipped EC2 instance.
3. Step 3: Inspect for TCP Retransmissions or Out-of-Order packets that indicate packet shaping or path instability.

Checkpoint Questions

1. What is the main difference between VPC Flow Logs and Traffic Mirroring in terms of data captured?
2. Which tool would you use to visualize the global topology of your Transit Gateway network?
3. If an instance has a high NetworkPacketsOut metric but low throughput, what might this indicate about the packet size?
4. How does CloudWatch help in establishing a network performance baseline?

Muddy Points & Cross-Refs

• Flow Logs vs. Mirroring: Flow logs are "after-the-fact" metadata (cheap, long retention). Mirroring is "real-time" packet capture (expensive, high overhead). Always start with Flow Logs.
• Reachability Analyzer vs. Route Analyzer: Reachability Analyzer is for VPC resources (SG/NACL/Route Tables). Transit Gateway Route Analyzer specifically tests routes across the TGW.
• MTU Mismatches: Often occur in hybrid VPN setups where the tunnel overhead reduces the effective MTU below 1500 bytes. Look for "ICMP Destination Unreachable" packets.

Comparison Tables