Port 3655: Unassigned — The Quiet Work of Render Farms

What Range This Port Belongs To

Port 3655 falls in the registered port range (1024–49151). These ports are managed by IANA, which maintains a registry of services that have formally requested a port assignment. Registration requires submitting a request and documenting the protocol.

Port 3655 has no such registration. IANA lists it as unassigned.¹

That doesn't mean it's quiet.

Known Unofficial Use: Autodesk Backburner

Autodesk Backburner is network rendering management software used with 3ds Max, Maya, Flame, and other Autodesk creative tools. It coordinates render farms — collections of computers that split animation rendering work across many machines simultaneously, finishing in hours what a single workstation would take days to complete.²

Backburner uses port 3655 as part of its communication between render managers and render servers. This use is documented in Autodesk's own support materials but was never formally registered with IANA.³

The primary Backburner ports are 3234 (Manager) and 3233 (Server). Port 3655 operates alongside them as an auxiliary communication channel. Studio IT teams configuring render farms need to open all three in their firewalls.

How to Check What's Listening on This Port

If you're curious what's using port 3655 on a machine:

macOS / Linux:

lsof -i :3655

Windows:

netstat -ano | findstr :3655

Cross-platform (with nmap):

nmap -p 3655 localhost

If you see Backburner's manager or server process, that's expected. If you see something else — and you didn't put it there — that's worth investigating.

Why Unassigned Ports Matter

The registered port range exists to prevent collisions: two different applications accidentally choosing the same port and fighting over it. When software uses an unassigned port without registering it, that guarantee disappears.

Backburner on port 3655 has mostly worked because render farm software runs on isolated studio networks, not the open Internet. Collision risk is low. But it's also why "what's on port X?" sometimes has no clean answer — the official record and the actual practice diverge.

The 65,535 ports available to TCP and UDP aren't enough for every application that's ever existed to have a formal home. Unassigned ports aren't failures of the system. They're the system working around its own limits.