Active Directory Configuration Issue ( The specified domain doesn't exist or cannot be contacted)

Hi,

We are facing issue with Active Directory connectivity. Getting the error "The specified domain doesn't exist or cannot be contacted/Server is not operational." while testing the connection from Sync Editor. It used to work fine and the issue occurred recently. Current version is 8.0

1) Able to take RDP of the AD server using the service account that we use to connect to AD.

2) Windows firewall is also not blocking the connection. 

3) Able to ping the AD server from our job server.

Please let know if there is any resolution for this.