Easily Fixed: TeamViewer Blocked by Firewall

TeamViewer getting blocked

TeamViewer is designed to establish remote connections to computers effortlessly without requiring specific firewall adjustments. In most instances, as long as internet browsing is feasible, TeamViewer functions smoothly. It initiates outbound connections to the internet, typically bypassing firewall restrictions. Nevertheless, in some instances, particularly within corporate environments governed by stringent security protocols, users may encounter TeamViewerblocked by firewall. This occurs when firewalls are configured to restrict all unidentified outbound connections.

What are the IP addresses and ports that TeamViewer uses?

To fix TeamViewer being blocked by firewall, you’ll need to find the destination IP addresses and the ports that TeamViewer uses.

Destination IP addresses

TeamViewer connects to its master servers worldwide, using different IP address ranges that frequently change. As a result, TeamViewer cannot provide a specific list of server IPs. However, all TeamViewer IP addresses have PTR records that resolve to "*.teamviewer.com". This information can be used to limit the destination IP addresses allowed through your firewall or proxy server. It gives you control over the connections allowed in your network.

Ports used by TeamViewer

These are the ports that TeamViewer needs to use.

• TCP/UDP Port 5938

For TeamViewer to function optimally, it relies primarily on outbound TCP and UDP connections through port 5938. TeamViewer prefers this port, and it is recommended to have your firewall allow traffic through this port at a minimum to ensure smooth operation.

• TCP Port 443

When TeamViewer encounters difficulties connecting over port 5938, it will attempt to establish a connection over TCP port 443 as an alternative. However, it's important to note that TeamViewer iOS and Windows Mobile mobile apps do not utilize port 443.

Please be aware that port 443 is also utilized by our custom modules generated in the Management Console. If you are deploying a custom module, such as through Group Policy, it is essential to ensure that port 443 is open on the target computers. It is worth mentioning that port 443 serves various other functions, including TeamViewer (Classic) update checks.

• TCP Port 80

In cases where connectivity through port 5938 or 443 is impossible, TeamViewer will attempt to establish a connection via TCP port 80. It's important to note that the connection speed over port 80 is slower and less reliable compared to ports 5938 and 443. This is due to the additional overhead it incurs, and there is no automatic reconnection in the event of a temporary loss of connection. As a result, port 80 is only utilized as a last resort.

It is worth mentioning that TeamViewer mobile apps on Windows Mobile do not employ port 80. However, the TeamViewer iOS and Android apps can utilize port 80 for connectivity if required.

How to fix TeamViewer blocked by firewall

Considering security implications, it is essential to note that TeamViewer strictly operates by initiating outbound data connections through firewalls. Consequently, from a security standpoint, it is typically adequate to block all incoming connections on the firewall and permit outgoing connections solely over port 5938, regardless of the destination IP address. When a firewall blocks TeamViewer, it usually suffices to open port 5938 on the firewall to restore functionality.

Step 1. Type "Windows firewall" in the search box on the Windows host computer and choose "Windows Firewall with Advanced Security".

Step 2. Click "Inbound Rules" and "New Rule".

Step 3. Select "Port" and click "Next".

Step 4. Click "Specific local ports" and enter the port number "5938" under "TCP".

Step 5. click "Allow the connection".

Step 6. Select the network types you want to use, name the rule, and hit "Finish".

Step 7. Now, TCP port 5938 is opened for TeamViewer in firewall rules. You shall not encounter TeamViewer blocked by firewall anymore.

Bonus tip: Best free TeamViewer alternative without firewall block

AnyViewer is a free remote desktop software designed explicitly for accessing Windows computers from a computer, iPhone, or Android device. It provides the convenience of controlling your remote PC without limitations on remote access or support.

One of the notable features of AnyViewer is its intelligent switching modes between UDP and TCP protocols. In most cases, when utilizing AnyViewer for remote access, there is no requirement to configure port permissions on the firewall. However, if the host computer has strict filtering rules, it may be necessary to open UDP ports 30196 and TCP ports 30192 and 30193.

Moreover, AnyViewer offers free usage for both personal and business purposes. While TeamViewer is commonly known as a free option for personal use, several users of the private version have reported being blocked from connecting even when not using TeamViewer for commercial purposes. The high pricing of TeamViewer's commercial versions often acts as a deterrent. This is why AnyViewer is considered the best alternative to TeamViewer.

Step 1. On both computers, download, install, and launch AnyViewer. Go to Log in on the Controller computer, and then click Sign up (if you have already signed up on its official website, you can log in directly).

Step 2. Fill out the signup form.

Step 3. You should now see that you have successfully logged into AnyViewer. Your device will be assigned to the account to which you have logged in automatically.

Step 4. Sign in with the same AnyViewer account on both computers, then click the One-click control for unattended remote access.

Notes:✎...

It is recommended to upgrade your account to a Professional or Enterprise plan. What can a professional or enterprise plan brings to you:

More devices will be allowed to assign to the same account for unattended access.

More connection channels for more devices to be able to start remote connection at the same time.

One device can connect to more devices simultaneously.

Black the remote PC screen and disable the remote keyboard & mouse click to protect privacy.

Transfer 1TB files at 10 MB/s.

The bottom line

This post introduces how to fix TeamViewer blocked by firewall. Besides, AnyViewer emerges as a reliable and free remote desktop software, offering seamless access to Windows computers from various devices. With its intelligent switching modes and minimal firewall configuration requirements, it presents itself as a viable alternative to TeamViewer, catering to personal and business needs.