Port 21553 (rdm-tfs)

IANA assigns port 21553 to rdm-tfs: Raima RDM TFS.

Registered (user) port, 1024-49151 TCP

IANA assignment

Service nameProtoDescriptionAssigneeReference

rdm-tfs TCP Raima RDM TFS Paul Johnson -

Registry dates for this port: registered 2011-05-02.

Linux: is anything listening on TCP 21553?

sudo ss -tlnp 'sport = :21553'

Linux / macOS: which process owns the port

sudo lsof -nP -i :21553

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':21553 '

Windows (Command Prompt)

netstat -ano | findstr :21553

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 21553 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 21553

From Windows

Test-NetConnection HOST -Port 21553

ufw

sudo ufw deny 21553/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 21553 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 21553 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 21553' -Direction Inbound -Protocol TCP -LocalPort 21553 -Action Block

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