Skip to main content
CrashPlan Support

Unable To Back Up To Another Computer

Applies to:
  • CrashPlan for Home
Need enterprise or small business documentation?
This article is intended for CrashPlan for Home users. For Code42 CrashPlan and CrashPlan for Small Business documentation, read this page on our enterprise support site.


If you are unable to connect to another computer, the status indicator for the destination on the Backup tab is typically grey instead of green. Additionally, you may see one of the following messages:

  • Disconnected, retrying in X
  • Unable to back up - no connection
  • Waiting for connection
  • Connecting to Backup Destination

Follow the troubleshooting steps in this article to identify and remedy the issue. For issues with connecting to CrashPlan Central, see Unable To Back Up To CrashPlan Central.


Computer-to-computer backup (backing up to a computer you own or a friend's computer)


  • By default, the CrashPlan app uses port 4242 for computer-to-computer backup. If the default port is already in use by another application, then a different port is used. The port in use by the CrashPlan service can be found by identifying ports used by the CrashPlan app.
  • When backing up to another computer, the router and firewall settings must be properly configured on each computer involved.
  • CrashPlan uses Universal Plug and Play (UPnP) and NAT Port Mapping Protocol (Nat-PMP) for computer-to-computer communication. If you previously disabled UPnP or NAT-PMP on your router, you must configure port forwarding to allow computer-to-computer backup.

Recommended solution

Start by manually instructing the CrashPlan app to reconnect with the other computer. This is an easy catch-all solution that can repair a disruption in the connection. Simply enter the restart command in the CrashPlan app's Command window:

  1. Open the CrashPlan app.
  2. Double-click the CrashPlan logo in the upper-right corner.
    The CrashPlan command-line area opens.
  3. Enter this command:
  4. Press Enter.
    This closes the CrashPlan app, stops the CrashPlan service, and then restarts the CrashPlan service.
  5. Open the CrashPlan app again.

If the backup destination for the other computer has a green circle near it, your CrashPlan app can connect and back up to it. If not, continue to Diagnosing Your Network Connection below.

Next steps: Diagnosing your network connection

If your CrashPlan app cannot contact the other computer after restarting, follow these steps to verify that your computer can make a network connection to the other computer.

Step 1: Identify the computer's network information

To test your connection to another computer, find the other computer's IP address and port.

On the other computer:

  1. Open the CrashPlan app.
  2. Go to Settings > Network.
  3. Record the other computer's Internal address and External address.
    Internal address and External address in the CrashPlan app

Step 2: Run telnet

Run the command telnet to diagnose the network connection between the two computers.

On your computer:

  1. Open a command prompt. (On Windows or macOS High Sierra 10.13, you must turn on Telnet before you can use it.)
    • Windows:
      • Windows 10 and Windows 8: Start > All Apps > Windows System > Command Prompt
      • Windows 7: Start > All Programs > Accessories > Command Prompt
    • OS X: Applications > Utilities > Terminal
    • Linux: Open Terminal or another command prompt for your distribution.
  2. Enter the telnet command with the other computer's network information.
    Example: telnet 4242
    • Use the Internal address if both computers are on the same network, such as being in the same house.
    • Use the External address if the computers are on different networks, such as being in different houses.

Step 3: Read the telnet response

If your command prompt shows the following Connected message, your CrashPlan app can successfully connect to the other computer:

telnet 443
Connected to
Escape character is '^]'.

If your command prompt shows anything else, your CrashPlan app cannot connect to the other computer. Common failure messages include:

  • Connection refused
  • Operation timed out
  • Unable to connect to remote host
  • No response

Step 4: Troubleshooting a failed connection

If your Telnet test did not connect to the other computer, your issue is caused by the configuration of your computers or network, not by the CrashPlan app. Check the following common causes of this issue:

  • Either computer's router, including its network configuration or port forwarding settings
  • Other conflicting software on either computer, such as antivirus, security, or parental control software

If you cannot connect to another computer after investigating these common causes, contact our Customer Champions.