What Is FTP? Plain FTP, FTPS, and SFTP Explained

FTP is a client-server protocol for transferring files, but “FTP,” “FTPS,” and “SFTP” are not interchangeable names. Plain FTP sends credentials and data without encryption. FTPS adds TLS to FTP. SFTP is a different protocol that transfers files over SSH.

Before entering a server address in an app, confirm which protocol the server actually supports. Choosing the wrong type can cause connection failures, and using plain FTP on an untrusted network can expose sensitive information.

How an FTP connection works

An FTP server exposes files and folders to authorized users. An FTP client connects with details such as:

• server hostname or IP address;
• protocol type;
• port;
• username and password or another supported credential;
• initial folder path; and
• active or passive data-connection behavior when relevant.

After authentication, the server may allow the client to list folders, upload files, download files, rename items, or delete them. The account's permissions determine which actions succeed.

FTP uses separate control and data connections. This design is one reason firewall, router, and passive-mode settings can affect a connection even when the username and password are valid.

Plain FTP

Plain FTP is the original unencrypted protocol. It may still appear in local NAS, legacy server, hosting, and equipment workflows.

Its main limitation is clear: usernames, passwords, and file contents are not protected by encryption. Do not expose plain FTP to the public internet for sensitive files, and do not use it on public or otherwise untrusted networks.

Even on a trusted local network, use a limited account and disable the service when it is not required.

FTPS

FTPS is FTP protected by TLS. It retains FTP's control/data connection model, so firewall and certificate configuration still matter.

An FTPS client and server must agree on how TLS is used. A plain FTP selection will not automatically negotiate every FTPS server, and accepting an invalid certificate defeats an important identity check.

Use the server administrator's exact instructions rather than guessing the security mode or port.

SFTP

SFTP is the SSH File Transfer Protocol. It is not FTP with a security checkbox; it uses SSH and has different server configuration and connection behavior.

SFTP is common in managed server and hosting workflows because it provides an encrypted connection and works with SSH account controls. A NAS or mobile app that supports FTP does not necessarily support SFTP, so verify both sides.

Protocol comparison

The table describes protocol design, not the security of a complete deployment. Account permissions, server updates, exposure, logging, and operational practices still matter.

Passive mode and connection failures

Because FTP-family workflows can use separate data connections, a client may authenticate successfully but fail when listing a folder or transferring a file.

Possible causes include:

• passive-mode configuration;
• blocked data ports;
• NAT or router behavior;
• a firewall on the server or client network;
• an incorrect initial path; or
• insufficient folder permissions.

Test a folder listing, a small download, and a small upload before attempting a large batch. Do not open a broad port range without understanding the server's documented requirements.

FTP is not backup or synchronization

FTP can copy a file. It does not automatically provide:

• version history;
• conflict resolution;
• automatic camera backup;
• deletion recovery;
• ransomware protection; or
• another independent copy.

Those features must come from the server, client application, and backup system around the protocol. Verify the destination and maintain a separate backup for irreplaceable files.

When an FTP-family protocol is appropriate

It may be a reasonable fit when:

• an existing NAS, hosting account, or server is already configured for it;
• a managed workflow requires SFTP or FTPS;
• direct server upload/download is the actual task;
• both client and server support the same secure protocol; and
• administrators can maintain credentials and server updates.

When to use another method

Choose another method when:

• the task is only to move files between nearby phone and computer;
• cloud synchronization or collaboration is required;
• the NAS vendor app provides the specific photo or backup feature needed;
• WebDAV or SMB is the approved existing service; or
• you cannot configure an internet-facing server safely.

For protocol choice, read FTP versus WebDAV. Neither is universally better; the server, security configuration, and client support determine the practical answer.

FTP-family access on iPhone

A compatible iPhone file manager can connect when you have the server's protocol, address, credentials, and permissions. Start on a trusted local network with a non-admin account and non-sensitive test files.

AirDisk can connect to supported FTP-family storage as an optional remote location. That is separate from its local browser-transfer workflow. AirDisk does not make an insecure plain FTP server safe or determine how the server is exposed.

For the setup workflow, use How to Access FTP from iPhone. If a connection succeeds, verify uploaded file size and open the destination file before deleting the source. If it fails, confirm the selected protocol first; changing passwords will not fix a client attempting FTP against an SFTP service.