Port 5281 (undo-lm)

IANA assigns port 5281 to undo-lm: Undo License Manager.

Registered (user) port, 1024-49151 TCP

IANA assignment

Service nameProtoDescriptionAssigneeReference

undo-lm TCP Undo License Manager Undo Ltd -

Registry dates for this port: registered 2010-04-19, last modified 2019-01-25.

Linux: is anything listening on TCP 5281?

sudo ss -tlnp 'sport = :5281'

Linux / macOS: which process owns the port

sudo lsof -nP -i :5281

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':5281 '

Windows (Command Prompt)

netstat -ano | findstr :5281

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 5281 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 5281

From Windows

Test-NetConnection HOST -Port 5281

ufw

sudo ufw deny 5281/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 5281 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 5281 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 5281' -Direction Inbound -Protocol TCP -LocalPort 5281 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.