Port 205 (TCP/UDP) sits in the well-known ports range (0-1023) with an official IANA assignment: "at-5" — AppleTalk Unused. This is unusual. Most ports are assigned because something needs them. Port 205 was assigned specifically to remain empty.
What AppleTalk Was
In April 1988, the Network Information Center assigned a block of UDP ports starting at 200 for AppleTalk's well-known DDP (Datagram Delivery Protocol) sockets.1 AppleTalk was Apple's networking protocol suite, designed to connect Macintosh computers, printers, and file servers in the era before TCP/IP became ubiquitous.
The block included:
- Port 201: AppleTalk Routing Maintenance
- Port 202: AppleTalk Name Binding
- Port 204: AppleTalk Echo
- Port 205: Deliberately unused
Port 205 was part of the reservation but marked as unused within the protocol itself. A placeholder. A gap in the sequence.
Why Assign an Unused Port
Protocol designers sometimes reserve ports they don't immediately need. Maybe they anticipated future expansion. Maybe they wanted clean numbering. Maybe they allocated a block and didn't use every slot.
Port 205 is that slot. It was never meant to carry AppleTalk traffic. It was meant to sit empty while its neighbors did the work.
Where AppleTalk Went
AppleTalk is obsolete. Apple deprecated it in Mac OS X 10.6 (2009) and removed it entirely in OS X 10.6 Server. The protocol that once connected schools, design studios, and offices full of Macs has been replaced by TCP/IP everywhere.
But the port assignments remain in the IANA registry. Port 205 is still officially "AppleTalk Unused" — a monument to a networking protocol that no longer exists.
What This Port Means Today
Port 205 is unassigned in practice. Because it's in the well-known range, it requires IETF Review or IESG Approval for official reassignment.2 But because AppleTalk is dead, no one is using it for its original purpose.
If something is listening on port 205 on your system, it's either:
- A legacy AppleTalk service (extremely unlikely)
- A custom application using an unoccupied port number
- Malware (port 205 has been used by trojans precisely because it's obscure)3
How to Check What's Listening
On Linux/macOS:
On Windows:
If nothing returns, nothing is listening. That's the expected state for port 205.
The Architecture of Empty Space
Port 205 is a reminder that the Internet's numbering system isn't just about what's assigned — it's also about what's deliberately left empty. Unassigned ports provide room for growth, gaps for safety, and space between services.
This port was reserved in an era when AppleTalk mattered. Now it sits unused in an obsolete protocol's abandoned block of the registry. It's not hurting anything. It's just there — officially assigned to nothing.
Security Considerations
Precisely because port 205 is obscure and unassigned, it's sometimes used by malware to avoid detection. If you find unexpected traffic on port 205, investigate it. Legitimate services rarely choose this port.
The emptiness is the point. When something occupies a deliberately unused port, pay attention.
Related Ports
- Port 201 (AppleTalk Routing Maintenance) - Managed routing updates between AppleTalk routers
- Port 202 (AppleTalk Name Binding) - Mapped names to addresses in AppleTalk networks
- Port 204 (AppleTalk Echo) - Tested connectivity in AppleTalk networks
- Port 206-207 (Unassigned) - More empty space in the well-known range
Frequently Asked Questions
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