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High port (10001–65535) Standard/Low risk

Port 21846 NETSPEAK-IS

Quick answer

Port 21846 is the IANA-assigned netspeak-is port for NetSpeak Corp. Directory Services (TCP / UDP).

Check and block Is it safe? Troubleshooting FAQ
TransportTCP / UDP
RiskStandard/Low
Typical useDirectory services

What is port 21846 used for?

Port 21846 is assigned to netspeak-is and uses TCP / UDP. The IANA registry describes the service as “NetSpeak Corp. Directory Services”. 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 netspeak-is connects to port 21846. A TCP connection is refused when nothing is listening, while a UDP request simply goes unanswered. That is why a port conflict appears whenever two processes try to bind the same number.

Use the commands below to confirm whether port 21846 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 Directory services ports

Source: IANA Service Name and Transport Protocol Port Number Registry. Registered assignee: [Toby_Hosterman].

Check and block port 21846

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 = :21846' sudo ss -ulpn 'sport = :21846'

Check on Windows

Get-NetTCPConnection -LocalPort 21846 -State Listen -ErrorAction SilentlyContinue Get-NetUDPEndpoint -LocalPort 21846 -ErrorAction SilentlyContinue

Block with UFW

sudo ufw deny 21846/tcp sudo ufw deny 21846/udp

Block with iptables

sudo iptables -A INPUT -p tcp --dport 21846 -j DROP sudo iptables -A INPUT -p udp --dport 21846 -j DROP

These 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 21846 safe to expose?

Standard/Low

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 21846 is usually used

Most traffic on port 21846 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.

Demo

Read the root DSE

The root DSE confirms the directory is answering before you test a specific base DN.

ldapsearch -H ldap://127.0.0.1:21846 -x -b "" -s base namingContexts

Common problems with port 21846

Connection refused or timed out

Refused usually means the host is reachable but nothing is listening on port 21846. 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 = :21846' or sudo lsof -i :21846. 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 21846 at a glance

Port number21846
Service namenetspeak-is
Transport protocolTCP / UDP
CategoryDirectory services
RangeHigh port (10001–65535)
Risk levelStandard/Low
Registered assignee[Toby_Hosterman]
Registry descriptionNetSpeak Corp. Directory Services
SourceIANA Service Name and Transport Protocol Port Number Registry

Frequently asked questions

What is port 21846 used for?

Port 21846 (NETSPEAK-IS) uses TCP / UDP. NetSpeak Corp. Directory Services.

How do I check if port 21846 is open?

On Linux run `sudo ss -tlpn 'sport = :21846'` and `sudo ss -ulpn 'sport = :21846'`. On Windows run `Get-NetTCPConnection -LocalPort 21846 -State Listen -ErrorAction SilentlyContinue` and `Get-NetUDPEndpoint -LocalPort 21846 -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 21846; empty output usually means nothing is bound to it.

How do I block port 21846?

With UFW run `sudo ufw deny 21846/tcp` and `sudo ufw deny 21846/udp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 21846 -j DROP` and `sudo iptables -A INPUT -p udp --dport 21846 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.

Is port 21846 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.

See all Directory services ports

Primary data: IANA Service Name and Transport Protocol Port Number Registry.

Last reviewed 2026-10-30 · Methodology · About · Privacy