Backup for an agent may fail with error messages like:
ERROR 2015-04-29T02:30:44  - Replay.Core.Implementation.Transfer.TransferJob ()
Job 'Transfer of volumes [C:\] from 'xxxxxxxxx'' failed
System.AggregateException: One or more errors occurred. ---> Replay.Core.Contracts.Transfer.CoreTransferFailedException: The transfer of one or more volume images from a protected machine to the Core has failed ---> System.AggregateException: One or more errors occurred. ---> Replay.Core.Contracts.Transfer.CoreVolumeTransferFailedException: The transfer failed for volume 'C:\' ---> System.Net.Sockets.SocketException: No such host is known
at System.Net.Dns.InternalGetHostByName(String hostName, Boolean includeIPv6)
at System.Net.Dns.GetHostAddresses(String hostNameOrAddress)
Key words are "No such host is known"