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Port 6621 (kftp)

IANA assigns port 6621 to kftp: Kerberos V5 FTP Control.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
kftp TCP Kerberos V5 FTP Control Robert J Scott -
kftp UDP Kerberos V5 FTP Control Robert J Scott -

Registry dates for this port: registered 2005-08.

Check what is listening on port 6621

Linux: is anything listening on TCP 6621?
sudo ss -tlnp 'sport = :6621'
Linux: UDP 6621
sudo ss -ulnp 'sport = :6621'
Linux / macOS: which process owns the port
sudo lsof -nP -i :6621
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':6621 '
Windows (Command Prompt)
netstat -ano | findstr :6621
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 6621 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 6621
From Windows
Test-NetConnection HOST -Port 6621
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 6621

Block port 6621 in the firewall

ufw
sudo ufw deny 6621/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 6621 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 6621 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 6621' -Direction Inbound -Protocol TCP -LocalPort 6621 -Action Block
ufw
sudo ufw deny 6621/udp
iptables
sudo iptables -A INPUT -p udp --dport 6621 -j DROP
nftables
sudo nft add rule inet filter input udp dport 6621 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 6621' -Direction Inbound -Protocol UDP -LocalPort 6621 -Action Block

Related ports

6619odette-ftps6620kftp-data6622mcftp6623ktelnet

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