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Port 671 (vacdsm-app)

IANA assigns port 671 to vacdsm-app: VACDSM-APP.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
vacdsm-app TCP VACDSM-APP - -
vacdsm-app UDP VACDSM-APP - -

Check what is listening on port 671

Linux: is anything listening on TCP 671?
sudo ss -tlnp 'sport = :671'
Linux: UDP 671
sudo ss -ulnp 'sport = :671'
Linux / macOS: which process owns the port
sudo lsof -nP -i :671
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':671 '
Windows (Command Prompt)
netstat -ano | findstr :671
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 671 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 671
From Windows
Test-NetConnection HOST -Port 671
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 671

Block port 671 in the firewall

ufw
sudo ufw deny 671/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 671 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 671 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 671' -Direction Inbound -Protocol TCP -LocalPort 671 -Action Block
ufw
sudo ufw deny 671/udp
iptables
sudo iptables -A INPUT -p udp --dport 671 -j DROP
nftables
sudo nft add rule inet filter input udp dport 671 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 671' -Direction Inbound -Protocol UDP -LocalPort 671 -Action Block

Related ports

669meregister670vacdsm-sws672vpps-qua673cimplex

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.