AWS Network Troubleshooting

June 27, 2026

This is a curated list of troubleshooting tips in AWS Cloud Environment. AWS Networking can become complex as a given infrastructure grows. Dealing with networking issues almost always comes down to understanding the building blocks and basics.

Public Access from Private Resource

Consider this case. AWS ec2 instance. you can telnet private ip of sftp family server but not the public ip address. When security group has 0.0.0.0/0, it works. When security group has VPC CIDR of ec2 instance, it does not work

curl ifconfig.me
curl https://checkip.amazonaws.com

If this returns a public IP, then your traffic to the SFTP server’s public endpoint, the public server or public facing resource is leaving the VPC through a NAT Gateway/Internet Gateway and re-entering AWS. The SFTP server, public ec2 instance or resource sees that public IP, not the EC2’s private IP. Adjust the security group accordingly