How to configure Linux Firewall for Soundlizer Connect

If an Android device cannot connect to Soundlizer Connect on Linux, the system firewall may be blocking the connection. Some Linux distributions, such as openSUSE and CachyOS, block incoming network connections by default.

Soundlizer Connect uses UDP to send visualization data to the Android device. The firewall must therefore allow incoming UDP traffic on the port specified in the Soundlizer Connect connection settings.

The default UDP port is 49251. If you changed the port in the program settings, use the corresponding value when configuring the firewall.

For convenience, you can enter the port used by Soundlizer Connect below:

The instructions below will automatically use the port you enter.

Before configuring the firewall

Make sure that the computer and Android device are connected to the same local network.

For example:

• the computer is connected to the router via Ethernet;
• the Android device is connected to the same router via Wi-Fi.

This is fine - the computer does not have to use Wi-Fi.

The devices must still be able to communicate directly with each other within the local network.

Check your Wi-Fi network settings

If the Android device is connected to a guest Wi-Fi network, the router may isolate it from other devices on the local network.

The router may also have AP Isolation or Client Isolation enabled. With this setting, devices may have internet access but cannot connect directly to each other.

The computer and Android device must be able to communicate with each other within the local network for Soundlizer Connect to work.

How to determine which firewall is being used

If you do not know which firewall is active on your system, check the most common options first:

UFW

sudo ufw status

firewalld

sudo firewall-cmd --state

nftables

sudo nft list ruleset

Your system may use more than one of these tools. For example, firewalld can manage nftables rules automatically.

UFW

UFW (Uncomplicated Firewall) is commonly used in Ubuntu, Debian, Linux Mint, CachyOS, and other distributions to manage firewall rules. It is disabled by default in Ubuntu, Debian, and Mint and therefore does not block the connection. In CachyOS, for example, it is enabled immediately after installation.

Check the UFW status

Open a terminal and run:

sudo ufw status

If you see:

Status: inactive

UFW is not blocking the connection - continue to the firewalld section.

If you see:

Status: active

UFW is enabled and may be blocking incoming connections. In this case, you need to allow the UDP port.

Allow the Soundlizer Connect UDP port

For the default port, run:

sudo ufw allow 49251/udp

Then check the rules:

sudo ufw status

The list should contain a rule for the UDP port 49251.

Restrict access to the local network (optional)

If you want to allow the port only within your local network rather than on all network interfaces, you can restrict the rule to a specific subnet.

For example:

sudo ufw allow from 192.168.1.0/24 to any port 49251 proto udp

Use the address of your local network instead of 192.168.1.0/24.

firewalld

Fedora, Red Hat, openSUSE, EndeavourOS, and some other Linux distributions use firewalld.

Check the firewalld status

sudo firewall-cmd --state

If the command returns:

running

firewalld is active.

Allow the UDP port

For the default Soundlizer Connect port:

sudo firewall-cmd --permanent --add-port=49251/udp

Then apply the changes:

sudo firewall-cmd --reload

You can check the active zones and open ports with:

sudo firewall-cmd --get-active-zones
sudo firewall-cmd --zone=public --list-ports

Important note about firewalld zones

firewalld uses network zones. If the computer has multiple network interfaces, the rule must apply to the zone used by the interface through which the Android device connects to the computer.

You can see the current active zones with:

sudo firewall-cmd --get-active-zones

If the standard --add-port command does not allow the connection, check the active zone and its interface settings.

nftables

If the system uses nftables directly, the rule must be added to the existing nftables configuration.

You can check the current rules with:

sudo nft list ruleset

If incoming connections are restricted by nftables rules, you need to allow UDP traffic on the Soundlizer Connect port.

The exact command depends on the existing nftables configuration. Do not add a universal rule without checking the current ruleset first.

If you manage nftables yourself, allow incoming UDP traffic on the port used by Soundlizer Connect in the appropriate chain of your configuration.

Soundlizer Connect cannot connect on Linux

If the UDP port is allowed but the Android device still cannot connect, check the network configuration.

1. Check the local network

The computer and Android device must be connected to the same local network.

The computer can use Ethernet while the Android device uses Wi-Fi.

2. Check the IP addresses

On Linux, you can view network interfaces and IP addresses with:

ip address

Make sure that the computer is connected to the correct local network.

3. Check for a guest Wi-Fi network

If the Android device is connected to a guest network, the router may prevent connections between clients.

Try using a regular Wi-Fi network instead.

4. Check AP Isolation / Client Isolation

If client isolation is enabled on the router, devices may have internet access but still be unable to connect to each other.

This isolation must be disabled for Soundlizer Connect to work.

5. Check your VPN

A VPN can change local traffic routing or block connections between local devices.

Try temporarily disabling the VPN and check the connection again.

6. Check for another firewall

Even if UFW or firewalld is inactive, the connection may still be blocked by another network filtering tool.

Check the firewall tools and network settings used by your system.

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