FTP - File Transfer Protocol

Enhanced Definition

File Transfer Protocol (FTP) is a standard network protocol used to transfer computer files from a server to a client on a computer network. In the z/OS environment, FTP facilitates the bidirectional movement of datasets and files between the mainframe and other systems (e.g., PCs, Unix servers, other mainframes) over a TCP/IP network. It enables both interactive and programmatic file exchange, making it a cornerstone for data integration in enterprise computing.

Key Characteristics

- Client-Server Model: The z/OS system can act as both an FTP client (initiating transfers to another system) and an FTP server (receiving connections and transfer requests from other systems).
- TCP/IP Based: FTP operates over the z/OS Communications Server's TCP/IP stack, utilizing TCP for reliable, connection-oriented data transfer.
- Dual Connections: It uses two separate TCP connections: a control connection (typically on port 21) for commands and responses, and a data connection (dynamic or port 20 for active mode) for the actual file transfer.
- Data Representation: Supports ASCII (for text files on non-mainframe systems), EBCDIC (for text files on z/OS), and BINARY (for non-text files like load modules, images, or compressed archives) modes for data conversion during transfer.
- Authentication: Requires user authentication, typically handled by the mainframe's external security manager (ESM) like RACF, ACF2, or Top Secret.
- Scriptable and Interactive: Can be used interactively via a TSO OMVS session or programmatically embedded in JCL, REXX, or shell scripts for automated batch processing.

Use Cases

- Batch Data Exchange: Transferring large sequential datasets, VSAM files, or PDS/PDSE members (e.g., daily transaction files, reports, extracts) between z/OS and distributed applications.
- Application Deployment and Maintenance: Uploading COBOL source code, JCL libraries, load modules, or configuration files from development workstations to z/OS.
- Log and Audit File Retrieval: Downloading system logs (e.g., CICS logs, DB2 logs, SMF data) or application-specific audit trails from the mainframe for analysis on other platforms.
- Developer Workflows: Enabling developers to transfer test data, program output, or diagnostic files between their local environments and the z/OS development environment.
- Automated Report Distribution: Automatically transferring generated reports from z/OS to network shares or other systems for further processing or distribution.

Related Concepts

FTP is an application layer protocol that relies heavily on the z/OS Communications Server (TCP/IP stack) for network connectivity. It interacts directly with z/OS dataset management facilities (SMS, catalog) to locate and manage files being transferred. In batch environments, FTP commands are often executed via the IKJEFT01 utility within JCL jobs, allowing for automated, scheduled transfers. User authentication and authorization for FTP access are managed by the mainframe's External Security Manager (ESM), such as RACF, which controls access to resources and datasets. The critical EBCDIC/ASCII conversion capability is essential for ensuring text files are readable across heterogeneous systems.

Best Practices:

Prioritize Secure FTP: Always use secure variants like FTPS (FTP over SSL/TLS) or SFTP (SSH File Transfer Protocol, though technically a different protocol) to encrypt data in transit, especially for sensitive information.
Explicitly Specify Data Type: Always use ASCII, EBCDIC, or BINARY commands to ensure correct data representation and prevent corruption, particularly when transferring text files between mainframe and non-mainframe systems.
Automate with JCL/Scripts: For recurring or high-volume transfers, embed FTP commands within JCL, REXX, or z/OS UNIX shell scripts to ensure consistency, reliability, and enable robust error handling.
Implement Robust Error Handling: Include checks for FTP return codes and implement appropriate error recovery or notification mechanisms within automated scripts to handle failed transfers gracefully.
Restrict Access and Permissions: Configure the z/OS FTP server and ESM rules (e.g., RACF profiles) to limit access to authorized users, specific IP addresses, and restrict file system permissions to the minimum necessary.
Monitor and Log Activity: Enable comprehensive logging on the z/OS FTP server and client to track transfer activity, identify potential issues, and maintain an audit trail.