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Port 623 (oob-ws-http, asf-rmcp)

IANA assigns port 623 to oob-ws-http, asf-rmcp: DMTF out-of-band web services management protocol.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
oob-ws-http TCP DMTF out-of-band web services management protocol Jim Davis -
asf-rmcp UDP ASF Remote Management and Control Protocol Carl First -

Registry dates for this port: registered 2007-06.

Check what is listening on port 623

Linux: is anything listening on TCP 623?
sudo ss -tlnp 'sport = :623'
Linux: UDP 623
sudo ss -ulnp 'sport = :623'
Linux / macOS: which process owns the port
sudo lsof -nP -i :623
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':623 '
Windows (Command Prompt)
netstat -ano | findstr :623
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 623 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 623
From Windows
Test-NetConnection HOST -Port 623
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 623

Block port 623 in the firewall

ufw
sudo ufw deny 623/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 623 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 623 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 623' -Direction Inbound -Protocol TCP -LocalPort 623 -Action Block
ufw
sudo ufw deny 623/udp
iptables
sudo iptables -A INPUT -p udp --dport 623 -j DROP
nftables
sudo nft add rule inet filter input udp dport 623 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 623' -Direction Inbound -Protocol UDP -LocalPort 623 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.