Port 447: DDM-DFM — IBM's Distributed File Management Port

Port 447 is officially assigned to DDM-DFM (Distributed Data Management - Distributed File Management), an IBM protocol for remote file and database access.¹² Every time an IBM i system (formerly AS/400, iSeries, System i) accesses a file or database on another machine, this is one of the ports that makes it happen.

What DDM-DFM Does

DDM (Distributed Data Management) is IBM's protocol for allowing programs on one IBM midrange system to access files and databases on another system as if they were local. Port 447 is one of three well-known ports (446, 447, 448) that DDM and DRDA (Distributed Relational Database Architecture) servers listen on.³

When a DRDA Application Requester or DDM client needs to connect, it reaches out to one of these three ports. The protocol handles:

• Remote file access across IBM i systems
• Distributed database queries
• Record-level access to files on remote machines
• Transaction coordination across systems

The Protocol

DDM was designed in an era when "distributed" meant connecting machines in the same data center, not across the Internet. It assumes a relatively trusted network and focuses on efficiency rather than security by modern standards.

The protocol operates over TCP, establishing a connection to port 446, 447, or 448 on the target system. Once connected, the client can open files, read records, write data, and execute database operations as if the remote files were local. The actual data transfer happens over this same connection.

History and Context

DDM emerged from IBM's midrange computing world—the AS/400 and its descendants. These systems became the backbone of countless businesses starting in the late 1980s, running everything from inventory management to payroll to manufacturing control.

The AS/400 was designed for reliability and ease of use. DDM was part of that design: make it simple for programs to access data regardless of where it physically lives. Port 447 and its siblings (446, 448) are the network manifestation of that philosophy.

These ports are still in active use today. IBM i systems remain widespread in industries like manufacturing, distribution, and finance—industries that value stability and uptime over novelty. The fact that port 447 is still carrying production traffic decades after its assignment is a testament to IBM's backward compatibility commitments.

Security Considerations

DDM was designed for trusted internal networks, not the modern Internet. If you're running IBM i systems:

• Never expose ports 446, 447, or 448 to the public Internet without additional security measures
• DDM connections should be protected with VPNs or other secure tunnels if crossing untrusted networks
• IBM i systems support SSL/TLS for DDM connections—use it
• Monitor and restrict which systems can connect to these ports
• Consider using IBM i's built-in security features to control DDM access at the user and object level

Port 447 carries sensitive business data. Treat it accordingly.

Checking Port 447

To see if something is listening on port 447:

# On Linux/macOS
sudo lsof -i :447
netstat -an | grep 447

# On Windows
netstat -ano | findstr :447

# Test connection to a remote system
telnet hostname 447
nc -zv hostname 447

If you see port 447 open and you're not running IBM i systems with DDM enabled, investigate immediately.

Related Ports

• Port 446: DDM-RDB (DDM Remote Database Access), another DDM/DRDA port
• Port 448: DDM-SSL (DDM over SSL), the secure variant
• Port 8470-8473: Additional ports used by IBM i for database access in some configurations

Why Port 447 Matters

Port 447 represents infrastructure that most people never see. It's running in hospitals managing patient records, in warehouses tracking inventory, in factories controlling production lines. These aren't sexy use cases. They're critical ones.

The IBM i systems using port 447 often have uptimes measured in years. They run the same programs that were written in the 1990s, accessing the same databases, serving the same business functions. This is infrastructure in the truest sense: invisible until it breaks, essential when it works.

Port 447 is a reminder that the Internet isn't just HTTP and HTTPS. It's also decades-old protocols carrying payroll data and purchase orders, still working, still essential, still invisible.