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Port 127 (locus-con)

IANA assigns port 127 to locus-con: Locus PC-Interface Conn Server.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
locus-con TCP Locus PC-Interface Conn Server Eric Peterson -
locus-con UDP Locus PC-Interface Conn Server Eric Peterson -

Check what is listening on port 127

Linux: is anything listening on TCP 127?
sudo ss -tlnp 'sport = :127'
Linux: UDP 127
sudo ss -ulnp 'sport = :127'
Linux / macOS: which process owns the port
sudo lsof -nP -i :127
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':127 '
Windows (Command Prompt)
netstat -ano | findstr :127
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 127 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 127
From Windows
Test-NetConnection HOST -Port 127
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 127

Block port 127 in the firewall

ufw
sudo ufw deny 127/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 127 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 127 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 127' -Direction Inbound -Protocol TCP -LocalPort 127 -Action Block
ufw
sudo ufw deny 127/udp
iptables
sudo iptables -A INPUT -p udp --dport 127 -j DROP
nftables
sudo nft add rule inet filter input udp dport 127 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 127' -Direction Inbound -Protocol UDP -LocalPort 127 -Action Block

Related ports

125locus-map126nxedit128gss-xlicen129pwdgen

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