CyberHunter
Local dataset, no network
// Network services

Port 63: whois++

Port 63 is assigned by IANA to whois++ (whois++), whoispp (whois++ IANA assigned this well-formed service name as a replacement for "whois++".).

63

How whois++ works

Network services
client:63whois++response client:63whois++response

The client sends a request to port 63 and the whois++ service answers.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned2 registered services
Range
Well-known (0-1023)
Category
Network services
01 Security

Is port 63 dangerous?

We have no specific security note for port 63. Its risk depends on the program actually listening on it. General advice for network services services:

  • Answer only the networks that need the service (no open resolvers, relays or reflectors).
  • UDP services can be abused for DDoS amplification: rate-limit or block them at the edge.
  • Disable legacy test services that have no use in production.
02 Registry

IANA registry entries for port 63

ServicePortTransportDescriptionReferenceUpdated
whois++ 63 TCP, UDP whois++ - -
whoispp 63 TCP, UDP whois++ IANA assigned this well-formed service name as a replacement for "whois++". - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 63, and is it reachable?

Linux

sudo ss -ltnup 'sport = :63'      # process listening on 63
sudo lsof -nP -i :63

macOS

sudo lsof -nP -i :63

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 63 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 63
netstat -ano | findstr :63

From another machine

nmap -p 63 -sV <host>
sudo nmap -sU -p 63 <host>
nc -zv <host> 63

Block it in the firewall

sudo ufw deny 63/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 63" -Direction Inbound -LocalPort 63 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 63 used for?

Port 63 is assigned by IANA to whois++ (whois++), whoispp (whois++ IANA assigned this well-formed service name as a replacement for "whois++".).

Is port 63 TCP or UDP?

Port 63 is registered for TCP and UDP.

Is it safe to open port 63?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Answer only the networks that need the service (no open resolvers, relays or reflectors).

How do I check if port 63 is open?

On Linux run "ss -ltnup 'sport = :63'", on macOS "lsof -nP -i :63", and on Windows "netstat -ano | findstr :63" to see the local process. From another machine, "nmap -p 63 <host>" shows whether it is reachable.

05 Related
:53 DNS tcp · udp · moderate risk :135 MS RPC tcp · udp · high risk :123 NTP udp · tcp · moderate risk :67 DHCP server udp · tcp · moderate risk :111 rpcbind tcp · udp · high risk :9100 Raw printing (JetDirect) tcp · udp · high risk :631 IPP / CUPS tcp · udp · high risk :5353 mDNS udp · tcp · moderate risk

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