Port: 1477
Service: MS-SNA-Server (Microsoft SNA Server)
Protocols: TCP, UDP
Port Type: Registered (User Port, 1024-49151)
What Port 1477 Does
Port 1477 is the registered port for Microsoft SNA Server, later renamed Host Integration Server. When a Windows PC needs to access data or applications on an IBM mainframe or AS/400 system, port 1477 is where that connection happens.
The SNA Server acts as a gateway—it receives requests from Windows clients over standard network protocols (TCP/IP, IPX, NetBEUI), then translates them into SNA (Systems Network Architecture) protocol that IBM mainframes understand. Port 1477 is the door clients knock on to reach that gateway.1
The Problem It Solved
In the 1990s, businesses faced an impossible situation. Their critical applications—payroll, inventory, customer records, transaction processing—lived on IBM mainframes and AS/400 systems. These systems represented decades of development and billions of dollars in investment. You couldn't just replace them.
But employees had Windows PCs on their desks. These two worlds spoke completely different languages. IBM mainframes used SNA, a protocol designed in 1974. Windows networks used TCP/IP, IPX, and other modern protocols. They couldn't talk to each other directly.
Microsoft introduced SNA Server in 1993 to solve this.2 It sat in the middle, translating between protocols. A Windows PC could send a request using TCP/IP to the SNA Server on port 1477, and the SNA Server would handle the complex job of speaking SNA to the mainframe.
How It Works
Here's the flow when a user accesses mainframe data:
-
Client request — A Windows application needs data from the mainframe. It connects to the SNA Server on port 1477 using a standard network protocol like TCP/IP.
-
Gateway translation — The SNA Server receives the request and translates it into SNA protocol. This involves handling session establishment, routing, and data formatting according to IBM's specifications.
-
Mainframe communication — The SNA Server forwards the translated request to the mainframe using protocols like 3270 (for terminal emulation), 5250 (for AS/400), or APPC (for program-to-program communication).3
-
Response path — When the mainframe responds, the SNA Server translates the response back into the Windows network protocol and sends it back to the client.
The SNA Server handled the heavy lifting. It supported up to 2,000 clients and 10,000 host sessions, managed hot backup and load balancing, and significantly improved performance compared to direct connections.4
The Architecture of Integration
Microsoft designed SNA Server with client-server architecture. Instead of each PC needing to understand SNA, they only needed to understand how to talk to the SNA Server. The SNA Server became the single point of expertise for mainframe communication.
The SnaBase service tracked which SNA servers were available in the domain, allowing clients to find and connect to the appropriate gateway. Port 1477 was the standard entry point for these connections.
This architecture offloaded processing from both the mainframe and the desktop PCs. Tests showed it could reduce AS/400 CPU utilization by 18%, improve response times by 33%, and generate 32% less network traffic compared to direct connections.5
Why This Port Matters
Port 1477 represents a specific pattern in enterprise computing: the gateway that bridges legacy and modern systems.
Mainframes didn't disappear when client-server computing arrived. They couldn't. They held too much critical data, ran too many essential applications, represented too much investment. Instead, enterprises needed ways to integrate old and new—to let modern applications access legacy data without rewriting everything.
Port 1477 was where that integration happened for millions of users. Every time an employee checked inventory on their Windows PC, processed a transaction, or accessed customer records stored on an IBM system, the request likely traveled through port 1477.
Microsoft eventually rebranded SNA Server to Host Integration Server in 2000, reflecting its broader role in connecting disparate systems.6 The technology has evolved, but the core problem remains: businesses still need to bridge different eras of computing.
Security Considerations
Port 1477 has been historically associated with malicious activity. Some trojans and viruses have used this port to communicate, likely because it's a legitimate enterprise port that might not be closely monitored.7
If you're running port 1477:
- Ensure you have a legitimate need for SNA Server or Host Integration Server
- Keep the software updated with security patches
- Monitor traffic for unusual patterns
- Restrict access to known clients and servers
- Block this port at the firewall if you're not using SNA/Host Integration Server
If you're not running SNA Server:
- Block port 1477 at your firewall
- Check if anything is listening on this port unexpectedly
- Investigate any traffic on this port as potentially malicious
Related Ports
- Port 1478 — Often associated with SNA-related services
- Port 1433 — Microsoft SQL Server, another enterprise data access port
- Port 3270 — The terminal emulation protocol used for IBM mainframe access
Checking Port 1477
To see if something is listening on port 1477:
Windows:
Linux/macOS:
If you see port 1477 open and you're not running Host Integration Server, investigate immediately.
The Bridge Between Eras
Port 1477 is more than a port number. It's a marker of when computing history had to bend to accommodate both the future (Windows networks) and the past (IBM mainframes).
The problem it solved—connecting modern interfaces to legacy systems—hasn't gone away. It's just moved. Today we build APIs to access ancient databases, microservices that talk to monolithic applications, cloud services that integrate with on-premise systems. The technology changes. The need for bridges doesn't.
Port 1477 carried one of those bridges. Every connection through this port was someone reaching across thirty years of computing history to get their work done.
האם דף זה היה מועיל?