How can we help?

We think these articles could help:

    See More
    Home > CrashPlan > Latest > Troubleshooting > Connections Between Computers

    Connections Between Computers

    Applies to:
    • CrashPlan for Home
    • CrashPlan PROe


    CrashPlan does its best to connect to other computers without configuration on your part, but sometimes you do need to adjust your firewall settings, especially after a CrashPlan upgrade or an operating system update. Follow this step-by-step guide to get your computers connected. 

    In rare cases after an update, some users who made no firewall modifications could experience difficulty connecting to other computers. Following an update, a software firewall might identify the new release as a new application. Adjusting the software firewall or enabling port forwarding usually resolves the issue, even if you've never had to do this before.

    Note: If you are using CrashPlan PROe, please see the CrashPlan PROe considerations below.


    If you are attempting to set up two or more computers to back up to each other (known as computer-to-computer backup), the router and firewall settings may need to be properly configured for each computer involved in a computer-to-computer relationship.

    IMPORTANT NOTE: The message "Unable to connect to the backup engine" is very rarely a network error. If you see this message, verify that no other applications are using the same ports CrashPlan needs to function. If that does not appear to be an issue, see our Unable to Connect to the Backup Engine article for further troubleshooting.

    CrashPlan PROe Considerations

    Multiple devices registered to the same user can be enabled to act as backup destinations for each other. CrashPlan PROe​'s NAT traversal feature is effective at allowing computer-to-computer backup between clients running on separate LANs.

    • Computer-to-computer backup is only allowed between computers owned by the same user account.
    • An administrator must enable the computer-to-computer backup feature (from Settings > Server, click Accept inbound backups)

    Recommended Solution

    Step 1: Re-authenticating With The Destination

    You can attempt to re-authenticate with CrashPlan Central if you cannot connect. 

    1. Open the CrashPlan app
    2. Double-click the CrashPlan logo in the upper-right and enter this command:
      ra, restart
    3. Press Enter
    4. Re-open the CrashPlan app

    Step 2: Check Software Firewall

    Create the following firewall rules in any software or hardware firewall between the relevant computers:

    • Allow inbound and outbound connections on TCP port 4242
      • Firewalls have rules for both incoming and outbound connections; a connection that works in one direction doesn't guarantee that it will work in another direction
      • Though most software firewalls allow you to make exceptions for specific programs, we recommend creating an exception for CrashPlan and for port 4242
    • Make an exception for the CrashPlan app in the software firewall
      • If you are unable to connect following an upgrade and already had a firewall exception for the CrashPlan app, add an exception for TCP port 4242.
        With an application exception, some firewalls may detect that CrashPlan has changed following an update and then stop allowing connections. A port exception is much more resilient.
    • Be sure to check the software firewall on both the source and destination computers.

    See External Resources for links to manufacturer documentation about software firewalls built into the Mac or Windows operating systems.

    CrashPlan Version Updates
    Upgrading the CrashPlan app to a new version may cause antivirus or security software​ to see that version as a new application and block its activity. If this occurs, re-add CrashPlan as an approved application in your antivirus or security software​.

    Step 3: Test With Telnet

    If the CrashPlan app is unable to connect to the other computer after configuring the firewalls and routers, you should use telnet to troubleshoot the connection. If telnet cannot connect to the other computer, then something is blocking the connection, such as:

    • a software firewall
    • a hardware firewall
    • incorrect port-forwarding on the router

    Step 4: Configure Port Forwarding

    If the telnet connection fails, enable port forwarding on your router for incoming connections on TCP port 4242.

    Enabling port forwarding is configured differently for each router manufacturer. You can review your manufacturer's documentation for details, or you can look for a guide at or HowToGeek.

    If the telnet connection succeeds and you still can't connect with CrashPlan, proceed to step 5.

    Step 5: Restart The Backup Service

    In some cases, after you configure port forwarding, you may need to restart the CrashPlan service on the source or the destination to get the network change to take effect.

    Step 6: Change The Listener Port

    If you have multiple computers running CrashPlan on a single network and you've tried everything up to this point, you may need to assign a unique listener port to each computer and configure port forwarding for each port. A symptom might be that one computer connects properly, but one does not.

    Good port choices are between 1024 and 5999. Ports 1023 and below are special and should not be used. Before you set a new port, you can use the netstat command to see if any other programs are using the port you've chosen.

    • Windows​: netstat -ano
    • Mac / Linux​: netstat -an

    Choose another port if something is already listed under the number you've selected.

    Once you find an unused port, you can change the listening port option in the CrashPlan app​ from Settings > General > Inbound backup from other computers>Listen port. Make sure to set up port forwarding for that port as well.

    You must to post a comment.
    Last Modified
    15:36, 14 Jul 2014

    Page Rating

    Was this article helpful?