Viscosity performs a "reachability check" before attempting to connect a VPN connection, or whenever a network change is detected. This check allows Viscosity to determine whether the remote VPN server can be reached over the network so the connection can be established. This check is also performed whenever your computer's network connection changes (e.g. you change wireless networks) to ensure that the VPN server can still be reached.

If a reachability check for a connection fails, Viscosity will abort the connection attempt and display the "Connection Name Could Not Be Connected Message" alert. You should also see a "Connection is not reachable. Disconnecting." message in the connection log.

Failure Reasons

A reachability check may fail for a number of reasons:

• Your computer isn't connected to a network. Check that your computer is correctly connected to your wired or wireless network. Try reconnecting to the network if you are unsure.

• Your computer doesn't have a valid network connection. Check that you can access other resources over your network, such as websites, to test your connection. Some pubic wireless and hotel networks may require you to open a page in your web browser before you can access the internet.

• The address for the remote VPN server is incorrect. Edit your connection and make sure the address is correct, or contact your VPN Provider to ensure your connections are valid and up-to-date.

• Viscosity could not resolve the address of the VPN server. Viscosity uses your computer's DNS servers to resolve a VPN server's domain address (e.g. myvpnserver.com) into an IP address it can connect to. If your computer's DNS servers are invalid, or they can not be reached, Viscosity will be unable to establish a connection. Check that your computer's DNS settings are valid. Alternatively you could try using Google's public DNS servers, or OpenDNS's servers.

• Viscosity could not find a valid network route to the VPN server. Viscosity checks your computer's internal network routing table to determine whether there is a network path to the remote VPN server. If there is no route that allows a connection the reachability check will fail. Check that there is no software installed, or other VPN connections active, that could interfere with your computer's routing table. Try restarting your computer to flush the routing table. If the reachability check only fails after your VPN connection has disconnected, see the Losing Network Connectivity Once Disconnected article.

Additional Troubleshooting

The connection log will also have additional information regarding the specific technical reason why the reachability check failed. These messages include:

• DNS resolution failed: The server's address could not be resolved via DNS. This likely means that the computer does not have a valid network connection, however it could also indicate that the server address is incorrect, the computer's DNS settings are invalid, or DNS resolution is being blocked.
• Route points to inactive interface: The computer has a valid network path to the remote server, however the network interface which it points to is inactive. This typically points to a network configuration problem on the local computer. Try restarting your computer and checking your local network configuration, and also check that the VPN server address is correct.
• Not Reachable: The VPN connection has no network route to the server. This likely means that the computer does not have a valid network connection.
• Not Reachable (IP Version): The VPN connection is only accessible over an IP version your machine does not support. For example it is only accessible via IPv6 and you are on an IPv4 only network.
• Route points into VPN network: The VPN connection is being routed into itself, creating a circular route. This is typically caused by an invalid routing configuration for the VPN connection, for example the OpenVPN server is pushing a network route to the client that encompasses the external address of the VPN server. If you’re the administrator of the VPN server, the correct way to fix this is to adjust the routes the server is pushing. If you're not the server administrator, or would like to resolve this on Viscosity's end, you can do the following:
  
  1. Edit your VPN connection in Viscosity and then click on the Networking tab.
  2. Click the small “+” button in the Routing section.
  3. Enter the server's external address in the Destination (without the quotes). Enter “32” as the Mask (no quotes) if the server is using IPv4, or "128" (no quotes) if the server is using IPv6. Select the IP Version the server is using. In most cases this will be IPv4. Select “Local Network Gateway” as the Gateway.
  4. Click the Add button, click Save and try connecting.