Port 63 (whoispp, whois++)

IANA assigns port 63 to whoispp, whois++: whois++ IANA assigned this well-formed service name as a replacement for "whois++"..

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

IANA assignment

Service nameProtoDescriptionAssigneeReference

whoispp TCP whois++ IANA assigned this well-formed service name as a replacement for "whois++". Rickard Schoultz -

whois++ TCP whois++
This entry is an alias to "whoispp". This entry is now historic, not usable for use with many common service discovery mechanisms. Rickard Schoultz -

whoispp UDP whois++ IANA assigned this well-formed service name as a replacement for "whois++". Rickard Schoultz -

whois++ UDP whois++
This entry is an alias to "whoispp". This entry is now historic, not usable for use with many common service discovery mechanisms. Rickard Schoultz -

Check what is listening on port 63

Linux: is anything listening on TCP 63?

sudo ss -tlnp 'sport = :63'

Linux: UDP 63

sudo ss -ulnp 'sport = :63'

Linux / macOS: which process owns the port

sudo lsof -nP -i :63

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':63 '

Windows (Command Prompt)

netstat -ano | findstr :63

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 63 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine

nc -vz -w 5 HOST 63

From Windows

Test-NetConnection HOST -Port 63

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 63

Block port 63 in the firewall

ufw

sudo ufw deny 63/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 63 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 63 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 63' -Direction Inbound -Protocol TCP -LocalPort 63 -Action Block

ufw

sudo ufw deny 63/udp