Port 750 KERBEROS-IV
Port 750 has a different IANA assignment for each transport protocol: TCP rfile; UDP kerberos-iv, loadav.
What is port 750 used for?
Port 750 carries a different IANA service on each transport protocol: TCP rfile; UDP kerberos-iv, loadav. It sits in the well-known range, which operating systems reserve for core network services, so software expects it at this number by default. The same port is also registered under rfile, loadav.
Each transport reaches a different service on this number, so match the protocol to the service you are diagnosing. A TCP check says nothing about a UDP listener on the same port, and the reverse is also true. Both transports still bind to the same number, which is why two processes can collide even when they use different protocols.
Use the commands below to confirm whether port 750 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 Authentication and access ports
Source: IANA Service Name and Transport Protocol Port Number Registry. Registered assignee: [Martin_Hamilton].
Check and block port 750
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 = :750'
sudo ss -ulpn 'sport = :750'Check on Windows
Get-NetTCPConnection -LocalPort 750 -State Listen -ErrorAction SilentlyContinue
Get-NetUDPEndpoint -LocalPort 750 -ErrorAction SilentlyContinueBlock with UFW
sudo ufw deny 750/tcp
sudo ufw deny 750/udpBlock with iptables
sudo iptables -A INPUT -p tcp --dport 750 -j DROP
sudo iptables -A INPUT -p udp --dport 750 -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 750 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 750 is usually used
Most traffic on port 750 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.
- Network devices authenticating users through a central service.
- Wi-Fi, VPN and remote-access gateways enforcing access policy.
- Accounting and session logs used for audits.
Probe the auth service
Authentication protocols are sensitive to shared secrets and source addresses, so test from an authorised client.
nc -vz 127.0.0.1 750Common problems with port 750
Connection refused or timed out
Refused usually means the host is reachable but nothing is listening on port 750. 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 = :750' or sudo lsof -i :750. 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 750 at a glance
| Port number | 750 |
|---|---|
| Service name | kerberos-iv |
| Aliases | rfile, loadav |
| Transport protocol | TCP / UDP |
| Assignments by protocol |
|
| Category | Authentication and access |
| Range | Well-known port (0–1023) |
| Risk level | Standard/Low |
| Registered assignee | [Martin_Hamilton] |
| Registry description | kerberos version iv |
| Source | IANA Service Name and Transport Protocol Port Number Registry |
Frequently asked questions
What is port 750 used for?
Port 750 (KERBEROS-IV). The IANA registry assigns a different service on each transport protocol: TCP rfile; UDP kerberos-iv, loadav.
How do I check if port 750 is open?
On Linux run `sudo ss -tlpn 'sport = :750'` and `sudo ss -ulpn 'sport = :750'`. On Windows run `Get-NetTCPConnection -LocalPort 750 -State Listen -ErrorAction SilentlyContinue` and `Get-NetUDPEndpoint -LocalPort 750 -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 750; empty output usually means nothing is bound to it.
How do I block port 750?
With UFW run `sudo ufw deny 750/tcp` and `sudo ufw deny 750/udp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 750 -j DROP` and `sudo iptables -A INPUT -p udp --dport 750 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.
Is port 750 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