Network Traffic Drop Due to Overlapping CIDR Blocks

Network traffic dropped due to overlapping CIDR blocks between the VPC and Kubernetes pod network.

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What Happened

Overlapping IP ranges between the VPC and pod network caused routing issues and dropped traffic between pods and external services.

Diagnosis Steps

1Reviewed the network configuration and identified the overlap in CIDR blocks.
2Used kubectl get pods -o wide to inspect pod IPs and found overlaps with the VPC CIDR block.

Root Cause

Incorrect CIDR block configuration during the cluster setup.

Fix/Workaround

• Reconfigured the pod network CIDR block to avoid overlap with the VPC.
• Re-deployed the affected pods and confirmed that traffic flow resumed.

Lessons Learned

Plan CIDR block allocations carefully to avoid conflicts.

How to Avoid

1Plan IP address allocations for both the VPC and Kubernetes network in advance.
2Double-check CIDR blocks during the cluster setup phase.