CyberHunter
Local dataset, no network
// Other services

Port 1681: sd-elmd

Port 1681 is assigned by IANA to sd-elmd (sd-elmd).

1681

How sd-elmd works

Other services
client:1681sd-elmdresponse client:1681sd-elmdresponse

The client sends a request to port 1681 and the sd-elmd 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 1681 dangerous?

We have no specific security note for port 1681. 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 1681

ServicePortTransportDescriptionReferenceUpdated
sd-elmd 1681 TCP, UDP sd-elmd - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 1681, and is it reachable?

Linux

sudo ss -ltnup 'sport = :1681'      # process listening on 1681
sudo lsof -nP -i :1681

macOS

sudo lsof -nP -i :1681

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1681 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 1681
netstat -ano | findstr :1681

From another machine

nmap -p 1681 -sV <host>
sudo nmap -sU -p 1681 <host>
nc -zv <host> 1681

Block it in the firewall

sudo ufw deny 1681/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 1681" -Direction Inbound -LocalPort 1681 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 1681 used for?

Port 1681 is assigned by IANA to sd-elmd (sd-elmd).

Is port 1681 TCP or UDP?

Port 1681 is registered for TCP and UDP.

Is it safe to open port 1681?

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 1681 is open?

On Linux run "ss -ltnup 'sport = :1681'", on macOS "lsof -nP -i :1681", and on Windows "netstat -ano | findstr :1681" to see the local process. From another machine, "nmap -p 1681 <host>" shows whether it is reachable.

05 Related
:4444 Metasploit default / krb524 tcp · udp · high risk :31337 Back Orifice / elite tcp · udp · high risk :1 TCP Port Service Multiplexer tcp · udp :5 Remote Job Entry tcp · udp :9 Discard tcp · udp · sctp · dccp :11 Active Users tcp · udp :17 Quote of the Day tcp · udp :18 Message Send Protocol (historic) tcp · udp

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