Port 16021 JWPC-BIN
Port 16021 is the IANA-assigned jwpc-bin port for Filemaker Java Web Publishing Core Binary (TCP).
What is port 16021 used for?
Port 16021 is assigned to jwpc-bin and uses TCP. The IANA registry describes the service as “Filemaker Java Web Publishing Core Binary”. It sits above the registered range, where most numbers are transient client ports. A fixed high port is worth documenting precisely because tooling often assumes the default.
Ports are the transport-layer address a service listens on. A client that wants to reach jwpc-bin connects to port 16021. If nothing is listening, the connection is refused. That is why a port conflict appears whenever two processes try to bind the same number.
Use the commands below to confirm whether port 16021 is actually in use before you change firewall rules. Blocking the port stops new inbound traffic at the firewall, but it does not stop a local process from listening, and it does not remove the service from the machine.
Source: IANA Service Name and Transport Protocol Port Number Registry. Registered assignee: [Robert_Parks].
Check and block port 16021
Copy-ready commands for the protocols assigned to this port. Run the check first, then block only what should not be reachable.
Check on Linux
sudo ss -tlpn 'sport = :16021'Check on Windows
Get-NetTCPConnection -LocalPort 16021 -State Listen -ErrorAction SilentlyContinueBlock with UFW
sudo ufw deny 16021/tcpBlock with iptables
sudo iptables -A INPUT -p tcp --dport 16021 -j DROPThese commands are examples for a typical host. Check the listener before you change firewall rules, and persist iptables rules with iptables-save or netfilter-persistent. On Windows, use Windows Defender Firewall or New-NetFirewallRule for persistent blocks. The iptables rules here cover IPv4; mirror them with ip6tables if IPv6 is enabled.
Is port 16021 safe to expose?
This port is not on our curated list of services with a widely exploited profile. Exposure is only safe when the listening service is intended, patched and protected by a firewall. Keep the listening service patched and remove it if unused. A default-deny firewall policy with explicit allow rules is still the safest baseline.
Where port 16021 is usually used
Most traffic on port 16021 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.
- Serving a website, API or reverse-proxy traffic that clients reach on port 16021.
- Load-balancer and uptime checks probing the port before routing requests.
- Local development, where a browser or curl calls the service on localhost:16021.
Send a test request
Start a local web server, then ask the port for response headers. Replace 127.0.0.1 with the host you are testing.
curl -I http://127.0.0.1:16021Common problems with port 16021
Connection refused or timed out
Refused usually means the host is reachable but nothing is listening on port 16021. A timeout more often means a firewall drop, a wrong host or a service bound to a different interface.
Port already in use
Find the process holding the port with sudo ss -tlpn 'sport = :16021' or sudo lsof -i :16021. Stop that process or configure it to bind another port; killing it without identifying it can take down a production service.
Firewall rule did not survive a reboot
UFW and Windows Firewall keep rules across restarts. Raw iptables rules do not: save them with iptables-save or the netfilter-persistent package, and re-apply after upgrades that reset the ruleset.
The port is blocked but still reachable
A firewall rule filters inbound traffic; it does not close the listener. Confirm with the check command above and bind the service to 127.0.0.1 when only local clients need it.
Port 16021 at a glance
| Port number | 16021 |
|---|---|
| Service name | jwpc-bin |
| Transport protocol | TCP |
| Category | Web and HTTP |
| Range | High port (10001–65535) |
| Risk level | Standard/Low |
| Registered assignee | [Robert_Parks] |
| Registry description | Filemaker Java Web Publishing Core Binary |
| Source | IANA Service Name and Transport Protocol Port Number Registry |
Frequently asked questions
What is port 16021 used for?
Port 16021 (JWPC-BIN) uses TCP. Filemaker Java Web Publishing Core Binary.
How do I check if port 16021 is open?
On Linux run `sudo ss -tlpn 'sport = :16021'`. On Windows run `Get-NetTCPConnection -LocalPort 16021 -State Listen -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 16021; empty output usually means nothing is bound to it.
How do I block port 16021?
With UFW run `sudo ufw deny 16021/tcp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 16021 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.
Is port 16021 safe to expose?
This port is not on our curated list of services with a widely exploited profile. Exposure is only safe when the listening service is intended, patched and protected by a firewall. Nevertheless, keep the listening service patched and remove it if unused. A default-deny firewall policy with explicit allow rules is still the safest baseline.
Related ports
Primary data: IANA Service Name and Transport Protocol Port Number Registry.
Last reviewed 2026-10-30 · Methodology · About · Privacy