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This article applies to Code42 for Enterprise version 5.

Other available versions:

Version 6 | Version 4icon.qnmark.png

Code42 Support

Test your network connection with Telnet

This article applies to Code42 for Enterprise version 5.

Other available versions:

Version 6 | Version 4icon.qnmark.png


Sometimes the Code42 CrashPlan app can't make a network connection even if the Internet appears to be working. This is because the CrashPlan app relies on specific ports to be open. This article describes how to use the Telnet client to test connectivity on the correct ports to rule out any sort of issue with firewalls, anti-virus products, or other network issues.

What are ports?

Ports are specific doorways for Internet traffic to travel through. If your computer were a building, ports would be numbered doors leading outside. If a door is locked, you can't get out. The CrashPlan app needs to open either of two specific doors: #443 and #4287. Other applications on your computer use other doors. So if your email and YouTube work, but the CrashPlan app does not, you should make sure that the proper ports are unlocked.

Before you begin

To use Telnet to troubleshoot a connection, you need to know the destination's address. If you do not know the address for your Code42 destination, contact your administrator.

Telnet use

Issue Telnet commands from the command prompt on your computer:

  1. Install Telnet if it is not already installed. (Telnet is not installed by default on Windows or on macOS High Sierra 10.13.)
  2. Open the command prompt:
    • Windows:
      1. Select Start.
      2. Choose Run or Search.
      3. Enter: cmd.exe
    • OS X: Select Utilities > Terminal.
    • Linux: Open Terminal.
  3. Enter the command: telnet <address of destination> <port>
    The CrashPlan app uses port 443, 4282 (non-TLS), or 4287 (TLS)  to connect to authority servers and the Code42 cloud. If you are unsure which port to include, test all.
    telnet 443
    telnet 4282
    telnet 4287

If Telnet successfully connects, a message displays similar to the following:

  • Linux and Mac
telnet 443
Connected to
Escape character is '^]'.
Connection closed by foreign host.

A non-TLS connection also returns an encrypted connection string (with unintelligible text) similar to the following:

  • Windows
    The successful connection message scrolls by quickly and you are presented with a blinking cursor on a blank screen. (You can press Enter to return to the command prompt.)

If Telnet cannot successfully connect, you may see one of the following messages, some other message, or no response: 

  • Connection refused
  • Operation timed out
  • Unable to connect to remote host
Use Telnet to isolate the issue
If the Telnet test passes, there probably isn't an issue with the network. However, some firewall and anti-virus applications are capable of blocking connections on a per-application basis, so please ensure that CrashPlan has an exception configured in your security software. If the problem continues, contact your administrator.
Ensure port 4287 is open
To communicate with the Code42 cloud, ensure that port 4287 is open. 

Install Telnet

Install Telnet on Windows

Telnet is not installed by default on Windows; if you try to run it you will get the message "'Telnet' is not recognized as an operable program or batch file." To install Telnet:

  1. Click Start.
  2. Select Control Panel.
  3. Choose Programs and Features.
  4. Click Turn Windows features on or off.
  5. Select the Telnet Client option.
  6. Click OK.
    A dialog box appears to confirm installation. The telnet command should now be available.

Install Telnet on Macintosh

Telnet is not installed on macOS High Sierra 10.13. To install Telnet:

  1. Paste the following into the Macintosh terminal prompt to install Homebrew, an open-source software package management system:
/usr/bin/ruby -e "$(curl -fsSL"
  1. Run the following command in the terminal prompt to install Telnet:
brew install telnet
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