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Port 651 (ieee-mms)

IANA assigns port 651 to ieee-mms: IEEE MMS.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
ieee-mms TCP IEEE MMS Curtis Anderson -
ieee-mms UDP IEEE MMS Curtis Anderson -

Check what is listening on port 651

Linux: is anything listening on TCP 651?
sudo ss -tlnp 'sport = :651'
Linux: UDP 651
sudo ss -ulnp 'sport = :651'
Linux / macOS: which process owns the port
sudo lsof -nP -i :651
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':651 '
Windows (Command Prompt)
netstat -ano | findstr :651
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 651 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 651
From Windows
Test-NetConnection HOST -Port 651
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 651

Block port 651 in the firewall

ufw
sudo ufw deny 651/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 651 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 651 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 651' -Direction Inbound -Protocol TCP -LocalPort 651 -Action Block
ufw
sudo ufw deny 651/udp
iptables
sudo iptables -A INPUT -p udp --dport 651 -j DROP
nftables
sudo nft add rule inet filter input udp dport 651 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 651' -Direction Inbound -Protocol UDP -LocalPort 651 -Action Block

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