Port 76: DEOS — The Protocol That Vanished

Port 76 is assigned to DEOS, the Distributed External Object Store. Both TCP and UDP. Registered with IANA. Official. Documented in RFC 1700¹.

And that is nearly everything that survives.

What DEOS Was

DEOS stands for Distributed External Object Store. The name suggests a system for storing and retrieving objects across a network, a distributed storage protocol. The assignment covers both TCP port 76 and UDP port 76.

Beyond the name and the port number, no public specification exists. No RFC describes the protocol. No surviving documentation explains its wire format, its handshake, or what problems it solved. The protocol is a label in a registry and nothing more.

The Person Behind It

The IANA registry credits port 76 to Robert Ullmann, who worked at Prime Computer, Inc. in Framingham, Massachusetts². Ullmann was not a casual contributor to Internet standards. He authored or co-authored at least six RFCs:

• RFC 1090 (1989): SMTP on X.25³, describing how to carry email over packet-switched networks
• RFC 1154 (1990): Encoding Header Field for Internet Messages, co-authored with David Robinson⁴
• RFC 1183 (1990): New DNS RR Definitions, co-authored with Craig Everhart, Louis Mamakos, and Paul Mockapetris⁵
• RFC 1475 (1993): TP/IX: The Next Internet, a proposal for a next-generation Internet protocol⁶
• RFC 1476 (1993): RAP: Internet Route Access Protocol
• RFC 1707 (1994): CATNIP: Common Architecture for the Internet, co-authored with Michael McGovern⁷

Ullmann moved from Prime Computer to Process Software Corporation, then to Lotus Development Corporation in Cambridge. He was thinking about big problems: how to unify Internet protocols, how to carry data across incompatible networks, how to build the next generation of Internet infrastructure.

Port 76 was likely one piece of a larger vision. Whatever DEOS was meant to become, it never made it past the registration.

The Well-Known Port Range

Port 76 sits in the System Ports range (0 through 1023), also called the well-known ports⁸. These are controlled by IANA and, on Unix-like systems, require root privileges to bind. This range contains the foundational protocols of the Internet: HTTP on 80, HTTPS on 443, SSH on 22, DNS on 53.

Getting a port in this range required going through IANA's assignment process. Ullmann did that. He secured a well-known port for DEOS. That alone tells you he intended it to be a foundational service, not an experiment.

Port 76's Neighbors

The ports around 76 tell the story of early Internet infrastructure:

Port 76 sits between the batch computing era and the dawn of the web. A transitional moment, frozen in a number.

Security Considerations

Port 76 has no known active services in widespread use. Some security databases flag it because malware has historically used obscure ports to avoid detection⁹. This is true of nearly any unoccupied port number. If you see traffic on port 76, investigate. It should not be open on a production system unless you have a specific, documented reason.

Checking What Listens on Port 76

On macOS or Linux:

# Check if anything is listening on port 76
sudo lsof -i :76

# Or with netstat
sudo netstat -tlnp | grep :76

On Windows:

netstat -ano | findstr :76

If something is listening on port 76 and you did not put it there, that warrants investigation.

Why Unassigned Ports Matter

The Internet has 65,535 ports. Fewer than 1,200 have official IANA assignments. The rest are either registered for specific applications (ports 1024 through 49151) or reserved as ephemeral ports for temporary connections (49152 through 65535).

Port 76 is technically assigned, not unassigned. But the protocol it was assigned to never materialized into anything the world adopted. This is more common than you might think. The IANA registry is full of protocols that were registered with genuine intent and then faded. Each one represents someone who had a vision for how networked computers should communicate. Some of those visions became the infrastructure we depend on. Others became two lines in a text file.

DEOS is two lines in a text file. But Robert Ullmann was real. Prime Computer was real. The problem of distributed object storage was real, and the industry would spend the next three decades trying to solve it in different ways: NFS, CORBA, S3, IPFS.

Port 76 is a headstone for an idea that arrived too early, or in the wrong form, or without the momentum to survive. The port remains reserved. The door is still there. Nothing answers when you knock.