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// Other services

Port 199: SMUX

Port 199 is assigned by IANA to smux (SMUX).

199

How smux works

Other services
client:199smuxresponse client:199smuxresponse

The client sends a request to port 199 and the smux 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
Well-known (0-1023)
Category
Other services
01 Security

Is port 199 dangerous?

We have no specific security note for port 199. 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 199

ServicePortTransportDescriptionReferenceUpdated
smux 199 TCP, UDP SMUX - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 199, and is it reachable?

Linux

sudo ss -ltnup 'sport = :199'      # process listening on 199
sudo lsof -nP -i :199

macOS

sudo lsof -nP -i :199

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 199 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 199
netstat -ano | findstr :199

From another machine

nmap -p 199 -sV <host>
sudo nmap -sU -p 199 <host>
nc -zv <host> 199

Block it in the firewall

sudo ufw deny 199/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 199" -Direction Inbound -LocalPort 199 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 199 used for?

Port 199 is assigned by IANA to smux (SMUX).

Is port 199 TCP or UDP?

Port 199 is registered for TCP and UDP.

Is it safe to open port 199?

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 199 is open?

On Linux run "ss -ltnup 'sport = :199'", on macOS "lsof -nP -i :199", and on Windows "netstat -ano | findstr :199" to see the local process. From another machine, "nmap -p 199 <host>" shows whether it is reachable.

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