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ProtocolPorts

Port reference

Port 1900 (UDP) – SSDP/UPnP

Simple Service Discovery Protocol — the discovery layer of UPnP that lets devices find each other on a LAN.

udpRegistered

Quick facts

Transport
udp
Category
Registered
Risk level
High

Frequently targeted — restrict exposure and harden it.

Default state

Open by default on many home routers, smart TVs, printers, and IoT devices. Frequently and dangerously exposed to the internet.

What is port 1900 used for?

UDP 1900 carries SSDP (Simple Service Discovery Protocol), the discovery part of UPnP (Universal Plug and Play). It's how devices find each other automatically on a home network — your smart TV, media server (DLNA), game console, printer, and streaming apps like those that "cast" all use it to announce and locate services. It is enabled by default on most consumer routers and gadgets.

When would you open it?

SSDP/UPnP is designed for the local network and works there without any manual setup, so you essentially never need to forward 1900 across the internet. The only relevant choice is whether to leave UPnP enabled on your LAN for convenience, or disable it if you prefer to configure devices by hand.

Is it safe to open?

Never expose 1900 to the internet — open SSDP responders are heavily abused for DDoS amplification, so block it at the router's WAN side and keep it LAN-only. See the security notes below.

How to check if this port is open

Linux
ss -tulpn | grep :1900
nmap -sU -p 1900 <target>
Windows
netstat -ano | findstr :1900
Test-NetConnection <host> -Port 1900   # TCP only
macOS
lsof -i :1900
nmap -sU -p 1900 <target>

How to open this port on your router

To reach this service from outside your network, forward the port on your router:

  1. Open your router's admin page (usually http://192.168.1.1 or http://192.168.0.1) and sign in.
  2. Find the "Port Forwarding" section — it may be called NAT, Virtual Server, or Applications & Gaming.
  3. Add a rule forwarding external port 1900 to your device's local IP, internal port 1900, protocol UDP.
  4. Save and reboot the router if prompted, then test the port from outside your network.

Only forward ports you understand — it exposes that device to the public internet. For remote admin access, a VPN is safer than forwarding the port.

Allow this port through the firewall

Linux (ufw)
sudo ufw allow 1900/udp
Linux (firewalld)
sudo firewall-cmd --permanent --add-port=1900/udp
sudo firewall-cmd --reload
Linux (iptables)
sudo iptables -A INPUT -p udp --dport 1900 -j ACCEPT
Windows
New-NetFirewallRule -DisplayName "Allow 1900" -Direction Inbound -Protocol UDP -LocalPort 1900 -Action Allow

Security & risks

Common attacks

  • SSDP reflection / amplification DDoS
  • Exposed UPnP control abuse (port mapping, NAT manipulation)
  • Device and network reconnaissance

Hardening

  • Block UDP 1900 inbound at the internet edge
  • Disable UPnP/SSDP on the WAN interface of routers
  • Turn off UPnP entirely where it isn't needed
  • Patch IoT/router firmware and segment IoT devices

How to block this port

Linux (ufw)
sudo ufw deny 1900/udp
Linux (firewalld)
sudo firewall-cmd --permanent --remove-port=1900/udp
sudo firewall-cmd --reload
Linux (iptables)
sudo iptables -A INPUT -p udp --dport 1900 -j DROP
Windows
New-NetFirewallRule -DisplayName "Block 1900" -Direction Inbound -Protocol UDP -LocalPort 1900 -Action Block

nmap snippet

nmap -sU -p1900 --script upnp-info <target>

Replace <target> with the host or range you're authorized to scan.

Related ports

Port 5000Port 5353Port 53Port 137

Frequently asked questions

What is port 1900 used for?
UDP 1900 carries SSDP, the discovery protocol behind UPnP. Devices use it to announce and find services on a local network — it should never be reachable from the internet.
Why is SSDP a DDoS risk?
A small SSDP M-SEARCH query yields a much larger reply, so internet-exposed devices are abused as reflectors/amplifiers to generate high-volume DDoS against third parties.

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