The MTU 9001 Trap: Flaky Connections Over VPC Peering and VPN
Ping works. SSH works. But the moment the app sends a large payload over VPN or cross-region peering, it just… hangs. This is why.
Hi everyone 👋
This is a classic debugging trap that can burn a new DevOps engineer several days, precisely because the system never throws a clear error log.
😱 The confusing symptom Two EC2 instances in different VPCs, connected over VPC peering, VPN, or Direct Connect. Ping between them responds fine. SSH works fine too. But the moment the application transfers a large file, or sends a long JSON payload over an API call on that same connection, the request hangs indefinitely until it eventually times out.
