551
FTP
551 Page Type Unknown
Requested action aborted: page type unknown. The server does not recognize the requested page structure or format.
On this page
When You See This Code
When attempting a transfer with a page structure type the server does not support. This is extremely rare in modern FTP usage.
How to Fix
Switch to stream transfer mode (MODE S) and file structure (STRU F), which are universally supported by all FTP servers.
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
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 551 Page Type Unknown?
Requested action aborted: page type unknown. The server does not recognize the requested page structure or format.
When do you see FTP 551 Page Type Unknown?
When attempting a transfer with a page structure type the server does not support. This is extremely rare in modern FTP usage.
How to fix FTP 551 Page Type Unknown?
Switch to stream transfer mode (MODE S) and file structure (STRU F), which are universally supported by all FTP servers.