Troubleshooting Authentication Failure
All forms of remote connectivity should require some form of authentication to confirm that those trying to access the remote resources have permission to do so. As a network administrator, you can expect to become very familiar with authentication troubleshooting. Quite often, authentication errors result from users incorrectly entering usernames and/or passwords.
Authentication issues can also arise as a result of permissions changes in users' accounts. If you're troubleshooting remote connectivity and you have confirmed that the correct username and password are used, you should confirm that the user has the appropriate permissions to access the network.
The third and perhaps least likely cause for authentication failure is a downed authentication server. In such a circumstance, you are likely to receive numerous calls regarding authentication difficultynot just one or two.