Data peer IP error which aborts the data connection - reproducible with AWS EC2

[Ann-at-HREF]

This error message came up for me today after upgrading to the latest FileZilla Server.

<Date/Time> Info [Type] Message
<08-12-2023 07:15:38> FTP Session 3 34.xxx.xxx.12 (snip username) [Error] Data peer IP [172.xx.xx.xx] differs from control peer IP [34.xxx.xxx.12]: this shouldn't happen, aborting the data connection.

How to reproduce this error

You need two AWS EC2 machines which happen to be in the same region. Put FileZilla server on one of them. Put ncFtpPut client on the other one. ( Download the client from ​https://www.ncftp.com/ncftp/ )

When ncFtpPut tries to connect, probably due to some AWS routing optimizations, it comes through using the private IPv4 of the client machine instead of using the public IPv4. This accounts for the difference.

Hope that helps.

[Tim Kosse]

What does ​https://ftptest.net/ say about your server?

[Ann-at-HREF]

Thank you so much for the ​https://ftptest.net suggestion. It did not connect initially, and based on its error log, I quickly found the two issues that needed adjustment in my FileZilla server configuration. I had to specify the public ipv4 for passive, and I had to tweak my port range to match what I had open in the Windows firewall.

My issue is fully resolved.

Embarassed but very happy for the quick and extremely useful assistance.