# Firewalls

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### Firewalls

A machine running Gurobi Remote Services communicates with clients through a number of network ports on the server machine. By default, it uses ports 61000-65000. You generally don't need to be aware of the details, since in most cases the server will either silently allow Gurobi Remote Services to use these ports or it will ask you to confirm that these ports can be used. However, some situations require you to manually open these ports.

One notable example is Amazon EC2, where most network ports are closed by default. You'll need to create an EC2 Security Group (or modify your default group) when you start your instance in order to open these ports.

If for some reason our default port range is unavailable on your server, you can include a PORT= statement in both the client and the server license files to choose a different range. For example, the line:

PORT=43000