Port 786 carries Concert—a distributed programming language from IBM Research that tried to make network programming feel as natural as writing local code.
What Runs on Port 786
Concert/C is a language extension to ANSI C that integrates distributed computing primitives directly into the language. Instead of wrestling with low-level networking APIs, programmers could write distributed systems using constructs that looked like ordinary C code.
The protocol runs on both TCP and UDP port 786 and was officially registered by Josyula R. Rao of IBM.
How Concert Works
Concert/C simplifies interprocess communication by making it part of the language itself. Communications happen over a "binding"—essentially a C pointer to a remote message queue called a "port." When you have a pointer to a function with an associated port, you can make remote procedure calls (RPC) on that function as if it were local.1
The implementation supports:
- Remote procedure calls (RPC)
- Asynchronous messaging
- Process creation and termination
- Dynamic process connections
- Communication over Sun RPC, OSF/DCE, and UDP multicast
Think of it as trying to hide the network. You write code that looks local, but Concert handles the distributed communication underneath.
The History
Concert/C emerged from IBM's T.J. Watson Research Center in the early 1990s, when distributed computing was becoming essential but remained difficult to program correctly.
The language was presented at the USENIX Winter 1994 Technical Conference by Joshua S. Auerbach, Arthur P. Goldberg, Ajei S. Gopal, Mark T. Kennedy, and James R. Russell.2 At the time, several groups inside and outside IBM were actively using it.
The project ran on AIX 3.2, SunOS 4.1, Solaris 2.2, and OS/2 2.1—a snapshot of the Unix landscape in the mid-1990s. It was distributed via anonymous FTP from software.watson.ibm.com:/pub/concert, back when anonymous FTP was how open source happened.3
What Makes Concert Interesting
Concert represents a particular philosophy about distributed systems: that the complexity should be absorbed by the language, not imposed on the programmer. Instead of learning entirely new APIs for network communication, you extend your knowledge of C with a few new primitives.
This is different from modern approaches like REST APIs or gRPC, which treat distribution as an explicit concern. Concert tried to make it transparent—the network disappears behind familiar syntax.
Whether that's a good idea is debatable. Making distribution invisible can hide the fundamental truth that network calls are different from local calls—they're slower, they can fail in more ways, and they have different performance characteristics. But in 1994, when distributed programming was still exotic, lowering the barrier to entry had real value.
Current Status
Concert/C appears to be a historical artifact. While it was influential in research circles and saw real-world use in the 1990s, it hasn't evolved into a widely-used modern system. The computing landscape moved toward different models—web services, message queues, microservices architectures.
Port 786 remains officially assigned to Concert in the IANA registry, but you're unlikely to encounter active Concert traffic on modern networks.
Checking for Port 786 Activity
To see if anything is listening on port 786 on your system:
If you find something listening here that isn't Concert-related, it's worth investigating—unassigned or rarely-used ports sometimes get repurposed by malware or unauthorized services.
Related Ports
Concert/C communicated over multiple transport protocols:
- Port 111: Sun RPC portmapper, used for dynamic port assignment in Sun RPC
- Port 135: DCE/RPC endpoint mapper, used in OSF/DCE environments
Why This Port Matters
Port 786 represents an era when distributed computing was being actively reinvented. Before microservices, before REST, before modern RPC frameworks—researchers were experimenting with how to make multiple computers work together as if they were one.
Concert didn't win. But the problems it tried to solve—making distributed systems easier to program, hiding communication complexity, providing transparent remote calls—those problems never went away. They just got different answers.
Every modern RPC framework is a descendant of this kind of thinking. The syntax changes, the transports evolve, but the core question remains: how do you make talking to a remote machine feel as natural as calling a local function?
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