Port 623 IPMI / BMC
Port 623 is most commonly used by IPMI / BMC. The IANA registry lists TCP / UDP for this number.
What is port 623 used for?
Port 623 is most commonly used by IPMI / BMC. IPMI and BMC controllers commonly listen on UDP 623; the IANA registry lists asf-rmcp for that protocol and oob-ws-http for TCP. 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 asf-rmcp.
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 623 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: [Jim_Davis].
Check and block port 623
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 = :623'
sudo ss -ulpn 'sport = :623'Check on Windows
Get-NetTCPConnection -LocalPort 623 -State Listen -ErrorAction SilentlyContinue
Get-NetUDPEndpoint -LocalPort 623 -ErrorAction SilentlyContinueBlock with UFW
sudo ufw deny 623/tcp
sudo ufw deny 623/udpBlock with iptables
sudo iptables -A INPUT -p tcp --dport 623 -j DROP
sudo iptables -A INPUT -p udp --dport 623 -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 623 safe to expose?
IPMI and BMC out-of-band management frequently ships with default credentials and weak cipher suites. Keep it on a dedicated management VLAN. Treat this port as sensitive. Restrict it to trusted networks or a VPN, require authentication and logging, and never expose it directly to the public internet without a hardened gateway in front.
Where port 623 is usually used
Most traffic on port 623 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 623.
- Load-balancer and uptime checks probing the port before routing requests.
- Local development, where a browser or curl calls the service on localhost:623.
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://127.0.0.1:623Common problems with port 623
Connection refused or timed out
Refused usually means the host is reachable but nothing is listening on port 623. 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 = :623' or sudo lsof -i :623. 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 623 at a glance
| Port number | 623 |
|---|---|
| IANA service name | oob-ws-http |
| Commonly used by | IPMI / BMC |
| Aliases | asf-rmcp |
| Transport protocol | TCP / UDP |
| Assignments by protocol |
|
| Category | Web and HTTP |
| Range | Well-known port (0–1023) |
| Risk level | High |
| Registered assignee | [Jim_Davis] |
| Registry description | DMTF out-of-band web services management protocol |
| Source | IANA Service Name and Transport Protocol Port Number Registry |
Frequently asked questions
What is port 623 used for?
Port 623 (IPMI / BMC). The IANA registry assigns a different service on each transport protocol: TCP oob-ws-http; UDP asf-rmcp. IPMI and BMC controllers commonly listen on UDP 623; the IANA registry lists asf-rmcp for that protocol and oob-ws-http for TCP.
How do I check if port 623 is open?
On Linux run `sudo ss -tlpn 'sport = :623'` and `sudo ss -ulpn 'sport = :623'`. On Windows run `Get-NetTCPConnection -LocalPort 623 -State Listen -ErrorAction SilentlyContinue` and `Get-NetUDPEndpoint -LocalPort 623 -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 623; empty output usually means nothing is bound to it.
How do I block port 623?
With UFW run `sudo ufw deny 623/tcp` and `sudo ufw deny 623/udp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 623 -j DROP` and `sudo iptables -A INPUT -p udp --dport 623 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.
Is port 623 safe to expose?
IPMI and BMC out-of-band management frequently ships with default credentials and weak cipher suites. Keep it on a dedicated management VLAN. Nevertheless, treat this port as sensitive. Restrict it to trusted networks or a VPN, require authentication and logging, and never expose it directly to the public internet without a hardened gateway in front.
Related ports
Primary data: IANA Service Name and Transport Protocol Port Number Registry.
Last reviewed 2026-10-30 · Methodology · About · Privacy