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// Network services

Port 563: nntp protocol over TLS/SSL (was snntp)

Port 563 is assigned by IANA to nntps (nntp protocol over TLS/SSL (was snntp)).

563

How nntps works

Network services
client:563#%&@!x9response? client:563#%&@!x9response?

The client sends a request to port 563 and the nntps service answers. Everything is encrypted: someone on the path only sees unreadable bytes.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
EncryptedTLS or built-in crypto
IANA status
Assigned1 registered service
Range
Well-known (0-1023)
Category
Network services
01 Security

Is port 563 dangerous?

We have no specific security note for port 563. 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 563

ServicePortTransportDescriptionReferenceUpdated
nntps 563 TCP, UDP nntp protocol over TLS/SSL (was snntp) RFC 4642 2018-07-06

// source: IANA service name and port number registry

03 Check it

Which program uses port 563, and is it reachable?

Linux

sudo ss -ltnup 'sport = :563'      # process listening on 563
sudo lsof -nP -i :563

macOS

sudo lsof -nP -i :563

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 563 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 563
netstat -ano | findstr :563

From another machine

nmap -p 563 -sV <host>
sudo nmap -sU -p 563 <host>
nc -zv <host> 563

Block it in the firewall

sudo ufw deny 563/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 563" -Direction Inbound -LocalPort 563 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 563 used for?

Port 563 is assigned by IANA to nntps (nntp protocol over TLS/SSL (was snntp)).

Is port 563 TCP or UDP?

Port 563 is registered for TCP and UDP.

Is it safe to open port 563?

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 563 is open?

On Linux run "ss -ltnup 'sport = :563'", on macOS "lsof -nP -i :563", and on Windows "netstat -ano | findstr :563" to see the local process. From another machine, "nmap -p 563 <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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