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Port 173 (xyplex-mux)

IANA assigns port 173 to xyplex-mux: Xyplex.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
xyplex-mux TCP Xyplex Bob Stewart -
xyplex-mux UDP Xyplex Bob Stewart -

Check what is listening on port 173

Linux: is anything listening on TCP 173?
sudo ss -tlnp 'sport = :173'
Linux: UDP 173
sudo ss -ulnp 'sport = :173'
Linux / macOS: which process owns the port
sudo lsof -nP -i :173
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':173 '
Windows (Command Prompt)
netstat -ano | findstr :173
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 173 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 173
From Windows
Test-NetConnection HOST -Port 173
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 173

Block port 173 in the firewall

ufw
sudo ufw deny 173/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 173 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 173 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 173' -Direction Inbound -Protocol TCP -LocalPort 173 -Action Block
ufw
sudo ufw deny 173/udp
iptables
sudo iptables -A INPUT -p udp --dport 173 -j DROP
nftables
sudo nft add rule inet filter input udp dport 173 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 173' -Direction Inbound -Protocol UDP -LocalPort 173 -Action Block

Related ports

171multiplex172cl-1, cl/1174mailq175vmnet

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