Preconditions

Before you start your migration, you must do all of the following:

Set up a Magento 2 system that meets our system requirements

Set up your system using a topology and design that at least matches your existing Magento 1 system.
Install Magento 2
Do not start Magento 2 cron jobs
After installation back up or dump your Magento 2 database as soon as possible
Check that the Data Migration tool has a network access to connect the Magento 1 and Magento 2 databases

Open ports in your firewall so the migration tool can communicate with the databases
To provide redundancy in the event of unexpected issues, we advise you to replicate your Magento 1 database
Migrate Magento 1 extension code to Magento 2

Reach out to your extension providers to see if they have been ported yet