HTTPfy

Port 401 (ups)

IANA assigns port 401 to ups: Uninterruptible Power Supply.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
ups TCP Uninterruptible Power Supply Charles Bennett -
ups UDP Uninterruptible Power Supply Charles Bennett -

Registry dates for this port: registered 2008-08-29.

Check what is listening on port 401

Linux: is anything listening on TCP 401?
sudo ss -tlnp 'sport = :401'
Linux: UDP 401
sudo ss -ulnp 'sport = :401'
Linux / macOS: which process owns the port
sudo lsof -nP -i :401
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':401 '
Windows (Command Prompt)
netstat -ano | findstr :401
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 401 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 401
From Windows
Test-NetConnection HOST -Port 401
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 401

Block port 401 in the firewall

ufw
sudo ufw deny 401/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 401 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 401 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 401' -Direction Inbound -Protocol TCP -LocalPort 401 -Action Block
ufw
sudo ufw deny 401/udp
iptables
sudo iptables -A INPUT -p udp --dport 401 -j DROP
nftables
sudo nft add rule inet filter input udp dport 401 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 401' -Direction Inbound -Protocol UDP -LocalPort 401 -Action Block

Related ports

399iso-tsap-c2400osb-sd402genie403decap

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