HTTPfy

Port 3881 (idac)

IANA assigns port 3881 to idac: Data Acquisition and Control.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
idac TCP Data Acquisition and Control Chatziandreoglou Chr -
idac UDP Data Acquisition and Control Chatziandreoglou Chr -

Registry dates for this port: registered 2003-10.

Check what is listening on port 3881

Linux: is anything listening on TCP 3881?
sudo ss -tlnp 'sport = :3881'
Linux: UDP 3881
sudo ss -ulnp 'sport = :3881'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3881
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3881 '
Windows (Command Prompt)
netstat -ano | findstr :3881
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3881 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3881
From Windows
Test-NetConnection HOST -Port 3881
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3881

Block port 3881 in the firewall

ufw
sudo ufw deny 3881/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3881 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3881 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3881' -Direction Inbound -Protocol TCP -LocalPort 3881 -Action Block
ufw
sudo ufw deny 3881/udp
iptables
sudo iptables -A INPUT -p udp --dport 3881 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3881 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3881' -Direction Inbound -Protocol UDP -LocalPort 3881 -Action Block

Related ports

3879appss-lm3880igrs3882msdts13883vrpn

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.