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Port 3855 (opentrac)

IANA assigns port 3855 to opentrac: OpenTRAC.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
opentrac TCP OpenTRAC Scott Miller -
opentrac UDP OpenTRAC Scott Miller -

Registry dates for this port: registered 2003-08.

Check what is listening on port 3855

Linux: is anything listening on TCP 3855?
sudo ss -tlnp 'sport = :3855'
Linux: UDP 3855
sudo ss -ulnp 'sport = :3855'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3855
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3855 '
Windows (Command Prompt)
netstat -ano | findstr :3855
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3855 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3855
From Windows
Test-NetConnection HOST -Port 3855
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3855

Block port 3855 in the firewall

ufw
sudo ufw deny 3855/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3855 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3855 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3855' -Direction Inbound -Protocol TCP -LocalPort 3855 -Action Block
ufw
sudo ufw deny 3855/udp
iptables
sudo iptables -A INPUT -p udp --dport 3855 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3855 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3855' -Direction Inbound -Protocol UDP -LocalPort 3855 -Action Block

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3853sscan3854stryker-com3856informer3857trap-port

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