Task Statement 3.2: Monitor and analyze network traffic to troubleshoot and optimize connectivity patterns.
📘AWS Certified Advanced Networking – Specialty
(Using tools like Reachability Analyzer)
This topic is about checking whether your AWS network is correctly configured and behaves exactly as the design expects. In real AWS environments, many connectivity issues are caused not by outages, but by misconfigurations in routing, security rules, or network paths.
To pass the exam, you must understand:
- What “network verification” means in AWS
- How to validate connectivity between resources
- How tools like Reachability Analyzer work
- What kind of problems it detects
- How to interpret results and fix issues
1. What does “verifying network configuration” mean?
In AWS, verification means confirming that:
- A resource (like EC2, Lambda in VPC, RDS) can reach another resource or endpoint
- Traffic follows the correct path defined in architecture
- All network rules (routing, security, firewall-like controls) are correct
- No unintended blocking or exposure exists
This is not guesswork—you use AWS tools to simulate and test network paths before or during production.
2. Key AWS Services used for verification
2.1 Amazon VPC
Amazon Web Services (VPC service: Virtual Private Cloud)
A VPC is your isolated network environment in AWS. Everything happens inside it:
- Subnets
- Route tables
- Security Groups
- Network ACLs
Verification always starts by checking VPC-level design correctness.
2.2 AWS Reachability Analyzer
AWS Reachability Analyzer
This is the most important exam tool for this topic.
What it does:
It automatically checks whether a network path is reachable or blocked between two points.
Example targets:
- EC2 → EC2
- EC2 → Internet Gateway
- EC2 → RDS
- EC2 → Transit Gateway attachment
- Cross-VPC communication
3. How Reachability Analyzer works (important for exam)
It performs a logical path simulation, not live traffic testing.
It checks step-by-step:
- Source selection
- Example: EC2 instance ENI
- Destination selection
- Example: another EC2, IP address, or ENI
- It evaluates the full network path:
- Subnet route table
- Security Groups
- Network ACLs
- Internet Gateway / NAT Gateway
- Transit Gateway routing
- VPC peering rules
- It returns a result:
- Reachable
- Not reachable
- If blocked, it shows:
- Exact blocking component
- Reason for failure
4. What Reachability Analyzer checks (exam-critical)
You must know all these layers:
4.1 Security Groups
- Stateful firewall at instance level
- Must allow inbound/outbound traffic
- Common failure: missing port or CIDR
4.2 Network ACLs (NACLs)
- Stateless subnet-level firewall
- Must allow both inbound and outbound rules
- Common failure: missing return traffic rule
4.3 Route Tables
- Determines where traffic goes
- Common issues:
- Missing route to NAT Gateway
- Missing route to Transit Gateway
- Incorrect CIDR entry
4.4 Internet Gateway / NAT Gateway
- IGW for public internet access
- NAT for private subnet outbound access
- Common failure: private subnet missing NAT route
4.5 VPC Peering / Transit Gateway
- Inter-VPC routing
- Must have:
- Correct route tables
- Correct association and propagation
4.6 AWS Transit Gateway
AWS Transit Gateway
Used in large-scale architectures.
Reachability Analyzer checks:
- Attachment state
- Route propagation
- TGW route tables
5. Common exam scenarios
You will often see questions like:
Scenario 1: EC2 cannot reach another EC2
You use Reachability Analyzer to check:
- Security Group missing inbound rule
- NACL blocking ephemeral ports
- Route table missing VPC route
Scenario 2: Private EC2 cannot access internet
Analyzer finds:
- Missing NAT Gateway route in route table
- NAT Gateway not attached properly
Scenario 3: Cross-VPC communication failure
Analyzer shows:
- Missing VPC peering route
- Incorrect CIDR configuration
Scenario 4: On-premises connectivity failure (VPN/Direct Connect)
Analyzer identifies:
- Missing route propagation in TGW
- Incorrect route in VGW/TGW route table
6. AWS VPC Flow Logs (supporting tool)
Amazon VPC Flow Logs
Flow Logs help you:
- Record actual traffic (accepted/rejected)
- Verify if traffic is being blocked in real time
- Identify security group or NACL drops
Difference from Reachability Analyzer:
- Reachability Analyzer = “planned path check”
- Flow Logs = “real traffic observation”
7. Amazon CloudWatch Logs (supporting tool)
Amazon CloudWatch
Used to:
- Monitor network-related metrics
- Track VPC Flow Logs
- Alert on connection failures
8. How to interpret Reachability Analyzer results (very important)
If result = REACHABLE
- All network layers are correctly configured
- No action needed
If result = NOT REACHABLE
You must identify:
- First blocking component
- Type of issue:
- Security Group denial
- Route missing
- NACL drop
- Gateway issue
Then fix that layer first (not randomly).
9. Exam best practices (high scoring points)
To succeed in the exam, remember:
9.1 Always test logical path first
Use Reachability Analyzer before checking logs.
9.2 Use Flow Logs for confirmation
If Analyzer says “reachable” but issue persists, check Flow Logs.
9.3 Understand layered networking model:
Traffic must pass:
- Security Group
- NACL
- Route Table
- Gateway (IGW/NAT/TGW)
If any layer fails → connectivity fails.
9.4 Know common misconfiguration patterns:
- Missing return route
- Wrong CIDR block
- SG allows inbound but not outbound
- NACL blocking ephemeral ports
- TGW route not propagated
10. Summary (Exam-ready)
To verify AWS network configuration:
- Use Reachability Analyzer to simulate and validate connectivity paths
- Check all network layers:
- Security Groups
- NACLs
- Route Tables
- Gateways (IGW/NAT/TGW)
- Use VPC Flow Logs for real traffic analysis
- Use CloudWatch for monitoring and alerts
- Identify the exact blocking point and fix it systematically
