Error: Cannot connect to server RC1

While establishing a debug session with the secondary core by performing Download an error appears Cannot connect to server RC1. 

Possible solutions: 

1. Open ports 5235 and 5304.

Open these ports in the Windows Defender Firewall or any other hardware of software firewalls you are using.

When debugging multicore application winIDEA spawns multiple instances of winIDEA. Primary winIDEA communicates with all other instances via TCP/IP using ports 5235 and 5304, but in general ports can be assigned in winIDEA. Usually Windows Defender Firewall is the only firewall that blocks traffic between winIDEA instances.

Read more about Multi-core debugging in winIDEA Help. 

1.1. How to open the TCP/IP port in the Windows OS?

1. Open Windows Defender Firewall.

2. Click on the option Allow an app or feature through Windows Defender Firewall.

3. Select winIDEA and adjust to which group the changes will apply to (Domain, Private, Public).

If the app (winIDEA) is not already selected click Allow another app and follow the Wizard.

2. Manually add a port.

2.1. How to manually add a port in Windows OS?

1. Open Windows Defender Firewall.

2. Click on the option Advanced settings.

3. Click Inbound Rules.

4. Locate the winIDEA, double click on and adjust settings in the dialog.

3. Using API.

Configure the port  which allows you to control winIDEA running on one PC by running a script on another PC.

1. Open Tools menu / Options / isystem.connect dialog.

2. Check option Enable isystem.connect over TCP/IP.

4. How to verify if ports are blocked?

1. Ensure that Tools / Options / Enable isystem.connect over TCP/IP is enabled.

2. Run Help / Support / Run External isystem.connect Diagnostic.

If you get the following output in the command prompt window,  the Firewall blocks the communication between winIDEA instances.

5. Tips for working remotely.

Please refer to this topic.