There is a dedicated Azure SQL Pool in Azure Synapse Analytics. You are getting “Login failed for user `NT AUTHORITY\ANONYMOUS LOGON`. (Microsoft SQL Server, Error: 18456)” when accessing it. What may be the cause of this issue?

Answer options:

A.User doesn’t exist in master.
B.User doesn’t exist in a specific SQL database.
C.firewall blocking access
D.CTAIP error

Correct Answer: A
This error occurs due to one cause only. If the AD user is trying to connect to the master database and that user does not exist in the master, there are two ways to mitigate this error. One, we should specify the dedicated SQL pool to which we are trying to connect at the connection time. Second, add the user to master.
Option A is correct:It is the cause of the error.
Option B is incorrect: This error is caused when the user does not exist in the master and not any other specific database in the pool.
Option C is incorrect: There will be a connection timeout or related error if the firewall is blocking.
Option D is incorrect: It`s an error that can occur when a login has been created on the SQL Database master database, but not in the specific SQL database.
Reference: 
To know more, please refer to the docs below: 

https://docs.microsoft.com/en-us/azure/synapse-analytics/sql-data-warehouse/sql-data-warehouse-troubleshoot#connecting