Port 23053 GNTP
Port 23053 is the IANA-assigned gntp port for Generic Notification Transport Protocol (TCP).
What is port 23053 used for?
Port 23053 is assigned to gntp and uses TCP. The IANA registry describes the service as “Generic Notification Transport Protocol”. 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 gntp connects to port 23053. 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 23053 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.
Browse all Time synchronization ports
Source: IANA Service Name and Transport Protocol Port Number Registry. Registered assignee: [Growl_Project].
Check and block port 23053
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 = :23053'Check on Windows
Get-NetTCPConnection -LocalPort 23053 -State Listen -ErrorAction SilentlyContinueBlock with UFW
sudo ufw deny 23053/tcpBlock with iptables
sudo iptables -A INPUT -p tcp --dport 23053 -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 23053 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 23053 is usually used
Most traffic on port 23053 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.
- Servers synchronizing clocks with an internal or public time source.
- Troubleshooting clock drift that breaks TLS, logs or authentication.
- Restricting time services to trusted hosts so they cannot be used for amplification.
Confirm the time listener
Time protocols differ: NTP has its own query tools, while other time services may use a different request format. Confirm the local socket first, then use the daemon's own status command.
sudo ss -ulpn 'sport = :23053'Common problems with port 23053
Connection refused or timed out
Refused usually means the host is reachable but nothing is listening on port 23053. 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 = :23053' or sudo lsof -i :23053. 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 23053 at a glance
| Port number | 23053 |
|---|---|
| Service name | gntp |
| Transport protocol | TCP |
| Category | Time synchronization |
| Range | High port (10001–65535) |
| Risk level | Standard/Low |
| Registered assignee | [Growl_Project] |
| Registry description | Generic Notification Transport Protocol |
| Source | IANA Service Name and Transport Protocol Port Number Registry |
Frequently asked questions
What is port 23053 used for?
Port 23053 (GNTP) uses TCP. Generic Notification Transport Protocol.
How do I check if port 23053 is open?
On Linux run `sudo ss -tlpn 'sport = :23053'`. On Windows run `Get-NetTCPConnection -LocalPort 23053 -State Listen -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 23053; empty output usually means nothing is bound to it.
How do I block port 23053?
With UFW run `sudo ufw deny 23053/tcp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 23053 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.
Is port 23053 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