425
FTP
425 Can't Open Data Connection
Can't open data connection. The server was unable to establish the data channel needed for the file transfer.
On this page
When You See This Code
When a firewall or NAT is blocking the data connection, or the client failed to connect to the server's passive port.
How to Fix
Switch between active (PORT) and passive (PASV) modes. Check that your firewall allows the FTP data port range and that NAT is configured correctly.
Specification
Compare With
Guides
FTP Reply Codes: Understanding File Transfer Responses
DNS & Networking
TCP Three-Way Handshake and Connection Lifecycle
DNS & Networking
Essential Network Debugging Tools: ping, traceroute, mtr, and tcpdump
DNS & Networking
RFC 959: FTP Protocol Deep Dive
Protocol Deep Dives
TLS 1.3: Faster, Simpler, More Secure
Protocol Deep Dives
Migrating from FTP to SFTP: A Complete Transition Guide
Migration & Upgrades
HTTP Access Log Management: Rotation, Parsing, and Analysis
Production Infrastructure
Debugging Scenarios
Specifications
Glossary
Status Code
TLS Handshake
TCP/IP
Three-Way Handshake
Port Number
Firewall
Proxy Server (Forward Proxy)
Socket
Request-Response Model
RFC (Request for Comments)
Connection-Oriented
Half-Duplex
Text vs Binary Protocol
FTP Active Mode
FTP Passive Mode
FTP Control Channel
FTP Data Channel
SFTP (SSH File Transfer Protocol)
FTPS (FTP Secure)
FTP Reply Code
FTP Anonymous Access
FTP Transfer Mode (ASCII vs Binary)
FTP Resume (REST Command)
SCP (Secure Copy Protocol)
FTP Chroot Jail
WebDAV (Web Distributed Authoring and Versioning)
rsync
FTP MLSD (Machine-Readable Listing)
FTP NAT Traversal
Transfer Integrity
FTP over TLS (RFC 4217)
File Locking
Bandwidth Throttling
TLS Versions
Frequently Asked Questions
What is FTP 425 Can't Open Data Connection?
Can't open data connection. The server was unable to establish the data channel needed for the file transfer.
When do you see FTP 425 Can't Open Data Connection?
When a firewall or NAT is blocking the data connection, or the client failed to connect to the server's passive port.
How to fix FTP 425 Can't Open Data Connection?
Switch between active (PORT) and passive (PASV) modes. Check that your firewall allows the FTP data port range and that NAT is configured correctly.