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// Other services

Port 3699: Internet Call Waiting

Port 3699 is assigned by IANA to kpn-icw (Internet Call Waiting).

3699

How kpn-icw works

Other services
client:3699kpn-icwresponse client:3699kpn-icwresponse

The client sends a request to port 3699 and the kpn-icw service answers.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
Other services
01 Security

Is port 3699 dangerous?

We have no specific security note for port 3699. Its risk depends on the program actually listening on it. General advice for other services services:

  • Close the port if nothing on the host needs it.
  • Identify the process that listens on it (commands below) before opening it in a firewall.
  • Expose a service only to the networks that use it.
02 Registry

IANA registry entries for port 3699

ServicePortTransportDescriptionReferenceUpdated
kpn-icw 3699 TCP, UDP Internet Call Waiting - 2003-02

// source: IANA service name and port number registry

03 Check it

Which program uses port 3699, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3699'      # process listening on 3699
sudo lsof -nP -i :3699

macOS

sudo lsof -nP -i :3699

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3699 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3699
netstat -ano | findstr :3699

From another machine

nmap -p 3699 -sV <host>
sudo nmap -sU -p 3699 <host>
nc -zv <host> 3699

Block it in the firewall

sudo ufw deny 3699/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3699" -Direction Inbound -LocalPort 3699 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3699 used for?

Port 3699 is assigned by IANA to kpn-icw (Internet Call Waiting).

Is port 3699 TCP or UDP?

Port 3699 is registered for TCP and UDP.

Is it safe to open port 3699?

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. Close the port if nothing on the host needs it.

How do I check if port 3699 is open?

On Linux run "ss -ltnup 'sport = :3699'", on macOS "lsof -nP -i :3699", and on Windows "netstat -ano | findstr :3699" to see the local process. From another machine, "nmap -p 3699 <host>" shows whether it is reachable.

05 Related
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