HTTPfy

Port 3857 (trap-port)

IANA assigns port 3857 to trap-port: Trap Port.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
trap-port TCP Trap Port Norm Freedman -
trap-port UDP Trap Port Norm Freedman -

Registry dates for this port: registered 2003-08.

Check what is listening on port 3857

Linux: is anything listening on TCP 3857?
sudo ss -tlnp 'sport = :3857'
Linux: UDP 3857
sudo ss -ulnp 'sport = :3857'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3857
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3857 '
Windows (Command Prompt)
netstat -ano | findstr :3857
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3857 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3857
From Windows
Test-NetConnection HOST -Port 3857
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3857

Block port 3857 in the firewall

ufw
sudo ufw deny 3857/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3857 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3857 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3857' -Direction Inbound -Protocol TCP -LocalPort 3857 -Action Block
ufw
sudo ufw deny 3857/udp
iptables
sudo iptables -A INPUT -p udp --dport 3857 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3857 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3857' -Direction Inbound -Protocol UDP -LocalPort 3857 -Action Block

Related ports

3855opentrac3856informer3858trap-port-mom3859nav-port

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