AD Connector-Unable to connect to the On-Premises Active Directory

AD Connector uses Kerberos for authentication and authorization of AWS applications. LDAP is only used for user and group object lookups (read operations). With the LDAP transactions, nothing is mutable and credentials are not passed in clear text. Authentication is handled by an AWS internal service, which uses Kerberos tickets to perform LDAP operations as a user.

AD Connector needs to obtain the _ldap._tcp.<DnsDomainName> and _kerberos._tcp.<DnsDomainName> SRV records when connecting to your directory. You will get this error [2] if the service cannot obtain these records from the DNS servers that you specified when connecting to your directory. For more information about these SRV records, see SRV record requirements -- [1]

Error Link-

https://docs.aws.amazon.com/directoryservice/latest/admin-guide/prereq_connector.html#srv_records -- [1] https://docs.aws.amazon.com/directoryservice/latest/admin-guide/ad_connector_troubleshooting.html -- [2]