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// Other services

Port 6601: Microsoft Threat Management Gateway SSTP

Port 6601 is assigned by IANA to mstmg-sstp (Microsoft Threat Management Gateway SSTP).

6601

How mstmg-sstp works

Other services
client:6601mstmg-sstpresponse client:6601mstmg-sstpresponse

The client sends a request to port 6601 and the mstmg-sstp service answers.

Transport
TCP
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 6601 dangerous?

We have no specific security note for port 6601. 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 6601

ServicePortTransportDescriptionReferenceUpdated
mstmg-sstp 6601 TCP Microsoft Threat Management Gateway SSTP - 2009-05-04
-6601-Reserved--

// source: IANA service name and port number registry

03 Check it

Which program uses port 6601, and is it reachable?

Linux

sudo ss -ltnup 'sport = :6601'      # process listening on 6601
sudo lsof -nP -i :6601

macOS

sudo lsof -nP -i :6601

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 6601 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 6601
netstat -ano | findstr :6601

From another machine

nmap -p 6601 -sV <host>
nc -zv <host> 6601

Block it in the firewall

sudo ufw deny 6601/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 6601" -Direction Inbound -LocalPort 6601 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 6601 used for?

Port 6601 is assigned by IANA to mstmg-sstp (Microsoft Threat Management Gateway SSTP).

Is port 6601 TCP or UDP?

Port 6601 is registered for TCP.

Is it safe to open port 6601?

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 6601 is open?

On Linux run "ss -ltnup 'sport = :6601'", on macOS "lsof -nP -i :6601", and on Windows "netstat -ano | findstr :6601" to see the local process. From another machine, "nmap -p 6601 <host>" shows whether it is reachable.

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