Port 446 is the well-known port for DDM-RDB (DDM-Remote Relational Database Access), IBM's protocol for accessing relational databases on remote systems. If you've ever worked in enterprise IT, you've probably depended on port 446 without knowing it existed.
What Runs on Port 446
DDM-RDB is part of IBM's Distributed Data Management Architecture (DDM), which enables creating, managing, and accessing data on remote computers.1 Port 446 specifically handles relational database operations across IBM systems—primarily IBM i (formerly AS/400) and DB2 for z/OS.
When a DRDA client (like DB2 Connect) needs to query a database on an IBM i system, it connects through port 446. The DDM server listening on this port handles the requests, manages transactions, and returns results.2
Both TCP and UDP use port 446, though TCP is far more common for database connections that require reliable delivery.
How DDM-RDB Works
DDM was designed on object-oriented principles before "object-oriented" became a buzzword. The architecture defines:
- Objects: Databases, files, queues, and other resources
- Messages: Standardized requests and responses
- Protocols: Rules for how systems communicate
DDM-RDB builds on this foundation to support DRDA (Distributed Relational Database Architecture), IBM's standard for distributed database access. When you execute a SQL statement against a remote IBM database, DDM-RDB:
- Receives the SQL request from the client
- Translates it into DDM protocol messages
- Executes the query on the remote database
- Returns results using the same messaging framework
The protocol handles connection management, transaction coordination, and data conversion between different system architectures.
The History: Rochester's Database Revolution
In the early 1980s, IBM's SNA (Systems Network Architecture) team defined APPC (Advanced Program to Program Communications), a protocol that let programs on different computers talk to each other. Engineers at IBM's Rochester, Minnesota development laboratory saw an opportunity.3
They realized that IBM's mid-range systems—the computers running payroll, inventory, and order processing for thousands of companies—needed to share data across networks. Filing systems, printer services, and database access all needed a common architecture.
Between 1980 and 1993, IBM defined DDM.1 The architecture started with record-oriented files, then expanded to support hierarchical directories, streams, queues, and eventually relational databases. In 1990, IBM published DDM Architecture Level 3 and DRDA simultaneously, establishing the foundation for distributed database computing across their platform.
DDM became the base protocol for DRDA, with specialized objects named RDB (for relational database) and SQLAM (for SQL Application Manager) handling the database-specific operations.
The AS/400 (now IBM i) was a natural fit for DDM. When IBM merged the System/36 and System/38 into the AS/400, DDM became the standard way to access DB2/400 databases from remote systems.4
Why Port 446 Still Matters
Four decades later, port 446 is still running in production. Banks process transactions through it. Insurance companies query customer records across it. Manufacturing systems synchronize inventory data over it.
IBM i systems are deeply embedded in enterprise infrastructure. Many organizations have applications written in RPG or COBOL that have been running for 30+ years, and those applications use DDM-RDB to access databases on remote systems.
The protocol is remarkably stable. Systems designed in 1990 can still communicate with systems deployed in 2025 using the same DDM messages and protocols.
Security Considerations
Port 446 predates modern security thinking. The original DDM architecture assumed trusted networks—systems within the same enterprise, connected via SNA or early TCP/IP networks.
Modern security requirements:
- Encryption: DDM-RDB doesn't include built-in encryption. Sensitive database traffic should tunnel through VPNs or use network-level encryption
- Authentication: DDM relies on system-level authentication (IBM i user profiles, etc.), but these credentials can be transmitted without encryption on older configurations
- Firewall rules: Port 446 should only be open between trusted IBM systems that need database connectivity
- Network segmentation: Keep DDM traffic on internal networks, isolated from the Internet
If you're exposing IBM i databases to remote locations, use VPN tunnels or IBM's SSL/TLS support for DRDA connections rather than opening port 446 directly to the Internet.
Checking What's Listening
To see if DDM-RDB is running on a system:
On Linux/macOS:
On Windows:
On IBM i:
Look for connections on port 446. If you see a listener, you're running a DDM server.
Related Ports
- Port 447: DDM-SECURE (secure DDM connections)
- Port 3306: MySQL (modern open-source database protocol)
- Port 5432: PostgreSQL (modern open-source database protocol)
- Port 1521: Oracle TNS (enterprise database listener)
DDM-RDB is IBM's equivalent to these database protocols, tailored specifically for IBM's midrange and mainframe ecosystems.
Common Questions
Is port 446 still actively used?
Yes. IBM i systems remain widespread in enterprise environments (banking, insurance, manufacturing, retail), and DDM-RDB is the standard protocol for distributed database access across these systems.
Can I use port 446 for non-IBM databases?
No. DDM-RDB is specific to IBM's architecture. It's designed for IBM i, DB2 for z/OS, and related systems. Other databases use their own protocols.
Is DDM-RDB the same as DRDA?
DDM is the underlying architecture; DRDA is the relational database layer built on top of DDM. DDM-RDB refers to the DDM objects and protocols used to implement DRDA.
Should I open port 446 on my firewall?
Only if you have IBM systems that need to communicate across network boundaries. Port 446 should be restricted to trusted systems and protected with VPNs or network encryption.
Why is this called DDM-RDB instead of DRDA?
The IANA port registry uses the DDM object naming convention (RDB = relational database). DRDA is the broader architecture; DDM-RDB is the specific protocol implementation.
Port 446 is a time capsule. It carries protocols designed when Reagan was president, running on systems that process billions of dollars in transactions every day. The banks trust it. The insurance companies trust it. The manufacturers trust it. Four decades of uptime built on messages defined in Rochester, Minnesota, still flowing through the same port number, still connecting the same kinds of systems, still doing the same essential work: getting data from one place to another, reliably, every single time.
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