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Port 27 (nsw-fe)

IANA assigns port 27 to nsw-fe: NSW User System FE.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
nsw-fe TCP NSW User System FE Robert Thomas -
nsw-fe UDP NSW User System FE Robert Thomas -

Check what is listening on port 27

Linux: is anything listening on TCP 27?
sudo ss -tlnp 'sport = :27'
Linux: UDP 27
sudo ss -ulnp 'sport = :27'
Linux / macOS: which process owns the port
sudo lsof -nP -i :27
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':27 '
Windows (Command Prompt)
netstat -ano | findstr :27
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 27 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 27
From Windows
Test-NetConnection HOST -Port 27
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 27

Block port 27 in the firewall

ufw
sudo ufw deny 27/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 27 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 27 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 27' -Direction Inbound -Protocol TCP -LocalPort 27 -Action Block
ufw
sudo ufw deny 27/udp
iptables
sudo iptables -A INPUT -p udp --dport 27 -j DROP
nftables
sudo nft add rule inet filter input udp dport 27 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 27' -Direction Inbound -Protocol UDP -LocalPort 27 -Action Block

Related ports

24any private mail system25SMTP29msg-icp31msg-auth

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