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// Network services

Port 4881: SOCP Time Synchronization Protocol

Port 4881 is assigned by IANA to socp-t (SOCP Time Synchronization Protocol).

4881

How socp-t works

Network services
client:4881socp-tresponse client:4881socp-tresponse

The client sends a request to port 4881 and the socp-t service answers.

Transport
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
Network services
01 Security

Is port 4881 dangerous?

We have no specific security note for port 4881. 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 4881

ServicePortTransportDescriptionReferenceUpdated
socp-t 4881 UDP SOCP Time Synchronization Protocol - 2010-05-28
-4881-Reserved--

// source: IANA service name and port number registry

03 Check it

Which program uses port 4881, and is it reachable?

Linux

sudo ss -ltnup 'sport = :4881'      # process listening on 4881
sudo lsof -nP -i :4881

macOS

sudo lsof -nP -i :4881

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 4881 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 4881
netstat -ano | findstr :4881

From another machine

nmap -p 4881 -sV <host>
sudo nmap -sU -p 4881 <host>
nc -zv <host> 4881

Block it in the firewall

sudo ufw deny 4881/udp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 4881" -Direction Inbound -LocalPort 4881 -Protocol UDP -Action Block  # Windows
04 FAQ
What is port 4881 used for?

Port 4881 is assigned by IANA to socp-t (SOCP Time Synchronization Protocol).

Is port 4881 TCP or UDP?

Port 4881 is registered for UDP.

Is it safe to open port 4881?

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 4881 is open?

On Linux run "ss -ltnup 'sport = :4881'", on macOS "lsof -nP -i :4881", and on Windows "netstat -ano | findstr :4881" to see the local process. From another machine, "nmap -p 4881 <host>" shows whether it is reachable.

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