Hi all, My exchange 2010 SP1 started to experience connectivity issues: EVENT ID 2105, Source MSExchange ADAccess Process MSEXCHANGEADTOPOLOGYSERVICE.EXE (PID=1128). Exchange Active Directory Provider failed to obtain DNS records for domain jericho.local. DNS Priority and Weight for the Domain Controllers in this domain will be set to the default values 0 (priority) and 100 (weight). Process MAD.EXE (PID=5472). Exchange Active Directory Provider failed to obtain DNS records for domain jericho.local. DNS Priority and Weight for the Domain Controllers in this domain will be set to the default values 0 (priority) and 100 (weight). EVENT ID 54, Source MSExchange OWA The Active Directory system configuration session couldn't be retrieved. Exception message: "Active Directory server is not available. Error message: Active directory response: The LDAP server returned an unknown error.". EVENT ID 2070, Source MSExchange ADAccess Process MsFTEFD.exe (PID=7576). Exchange Active Directory Provider lost contact with domain controller . Error was 0x51 (ServerDown) (Active directory response: The LDAP server is unavailable.). Exchange Active Directory Provider will attempt to reconnect with this domain controller when it is reachable. First I thought it because AVG is installed on DC and on Exchange servers. But it continue even after AVG disabling. No problem with DC within Windows Logs. Also clients were unable to connect Outlook to Exchange. Outlook prompted for Login\pass. ipconfig /flushdns on each PC solved it. Please advice what can be wrong with exchange and network connection. Thanks, Nick