Update storage-sync-files-firewall-and-proxy.md

Added "Test network connectivity to service endpoints" section

Author: jeffpatt24

articles/storage/files/storage-sync-files-firewall-and-proxy.md

@@ -140,6 +140,15 @@ For business continuity and disaster recovery (BCDR) reasons you may have specif
 > - https:\//kailani1.one.microsoft.com (paired fail-over region: East US)
 > - https:\//tm-kailani.one.microsoft.com (discovery URL of the primary region)
 
+## Test network connectivity to service endpoints
+Once a server is registered with the Azure File Sync service, the Test-StorageSyncNetworkConnectivity cmdlet and ServerRegistration.exe can be used to test communications with all endpoints (URLs) specific to this server. This cmdlet can help troubleshoot when incomplete communication prevents the server from fully working with Azure File Sync and it can be used to fine tune proxy and firewall configurations.
+
+To run the network connectivity test, install Azure File Sync agent version 9.0 or later and run the following PowerShell commands:
+```powershell
+Import-Module "C:\Program Files\Azure\StorageSyncAgent\StorageSync.Management.ServerCmdlets.dll"
+Test-StorageSyncNetworkConnectivity
+```
+
 ## Summary and risk limitation
 The lists earlier in this document contain the URLs Azure File Sync currently communicates with. Firewalls must be able to allow traffic outbound to these domains. Microsoft strives to keep this list updated.