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Port 171 (multiplex)

IANA assigns port 171 to multiplex: Network Innovations Multiplex.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
multiplex TCP Network Innovations Multiplex - -
multiplex UDP Network Innovations Multiplex - -

Check what is listening on port 171

Linux: is anything listening on TCP 171?
sudo ss -tlnp 'sport = :171'
Linux: UDP 171
sudo ss -ulnp 'sport = :171'
Linux / macOS: which process owns the port
sudo lsof -nP -i :171
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':171 '
Windows (Command Prompt)
netstat -ano | findstr :171
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 171 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 171
From Windows
Test-NetConnection HOST -Port 171
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 171

Block port 171 in the firewall

ufw
sudo ufw deny 171/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 171 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 171 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 171' -Direction Inbound -Protocol TCP -LocalPort 171 -Action Block
ufw
sudo ufw deny 171/udp
iptables
sudo iptables -A INPUT -p udp --dport 171 -j DROP
nftables
sudo nft add rule inet filter input udp dport 171 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 171' -Direction Inbound -Protocol UDP -LocalPort 171 -Action Block

Related ports

169send170print-srv172cl-1, cl/1173xyplex-mux

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