Port 3121 PCMK-REMOTE
Port 3121 is the IANA-assigned pcmk-remote port for The pacemaker remote (pcmk-remote) service extends high availability functionality outside of the Linux cluster into remote nodes (TCP).
What is port 3121 used for?
Port 3121 is assigned to pcmk-remote and uses TCP. The IANA registry describes the service as “The pacemaker remote (pcmk-remote) service extends high availability functionality outside of the Linux cluster into remote nodes.”. It sits in the registered range, the block used by databases, application servers and developer tooling. Port conflicts here are common when several local services start at once.
Ports are the transport-layer address a service listens on. A client that wants to reach pcmk-remote connects to port 3121. 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 3121 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: [David_Vossel].
Check and block port 3121
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 = :3121'Check on Windows
Get-NetTCPConnection -LocalPort 3121 -State Listen -ErrorAction SilentlyContinueBlock with UFW
sudo ufw deny 3121/tcpBlock with iptables
sudo iptables -A INPUT -p tcp --dport 3121 -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 3121 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 3121 is usually used
Most traffic on port 3121 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.
- Application backends and supporting services that use a fixed registered number.
- Containers or local stacks that publish the port on the host.
- Firewall and exposure reviews before the service goes to production.
Probe the port
Confirm something is listening before you debug the client. This checks a TCP handshake on the port.
nc -vz 127.0.0.1 3121Common problems with port 3121
Connection refused or timed out
Refused usually means the host is reachable but nothing is listening on port 3121. 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 = :3121' or sudo lsof -i :3121. 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 3121 at a glance
| Port number | 3121 |
|---|---|
| Service name | pcmk-remote |
| Transport protocol | TCP |
| Category | Application services |
| Range | Registered port (1024–10000) |
| Risk level | Standard/Low |
| Registered assignee | [David_Vossel] |
| Registry description | The pacemaker remote (pcmk-remote) service extends high availability functionality outside of the Linux cluster into remote nodes. |
| Source | IANA Service Name and Transport Protocol Port Number Registry |
Frequently asked questions
What is port 3121 used for?
Port 3121 (PCMK-REMOTE) uses TCP. The pacemaker remote (pcmk-remote) service extends high availability functionality outside of the Linux cluster into remote nodes.
How do I check if port 3121 is open?
On Linux run `sudo ss -tlpn 'sport = :3121'`. On Windows run `Get-NetTCPConnection -LocalPort 3121 -State Listen -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 3121; empty output usually means nothing is bound to it.
How do I block port 3121?
With UFW run `sudo ufw deny 3121/tcp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 3121 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.
Is port 3121 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
- Port 3101 · hp-pxpibHP PolicyXpert PIB Server
- Port 3128 · ndl-aasActive API Server Port
- Port 3132 · ms-rule-engineMicrosoft Business Rule Engine Update Service
- Port 3098 · umm-portUniversal Message Manager
- Port 3166 · sossecollectorQuest Spotlight Out-Of-Process Collector
- Port 3090 · stssSenforce Session Services
Primary data: IANA Service Name and Transport Protocol Port Number Registry.
Last reviewed 2026-10-30 · Methodology · About · Privacy