Configuring Network Security Group Flow logs with PowerShell

Network Security Group flow logs are a feature of Network Watcher that allows you to view information about ingress and egress IP traffic through a Network Security Group. These flow logs are written in json format and show outbound and inbound flows on a per rule basis, the NIC the flow applies to, 5-tuple information about the flow (Source/Destination IP, Source/Destination Port, Protocol), and if the traffic was allowed or denied.

Register Insights provider

In order for flow logging to work successfully, the Microsoft.Insights provider must be registered. If you are not sure if the Microsoft.Insights provider is registered, run the following script.

Register-AzResourceProvider -ProviderNamespace Microsoft.Insights

Enable Network Security Group Flow logs and Traffic Analytics

The command to enable flow logs is shown in the following example:

$NW = Get-AzNetworkWatcher -ResourceGroupName NetworkWatcherRg -Name NetworkWatcher_westcentralus
$nsg = Get-AzNetworkSecurityGroup -ResourceGroupName nsgRG -Name nsgName
$storageAccount = Get-AzStorageAccount -ResourceGroupName StorageRG -Name contosostorage123
Get-AzNetworkWatcherFlowLogStatus -NetworkWatcher $NW -TargetResourceId $nsg.Id

#Traffic Analytics Parameters
$workspaceResourceId = "/subscriptions/bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb/resourcegroups/trafficanalyticsrg/providers/microsoft.operationalinsights/workspaces/taworkspace"
$workspaceGUID = "cccccccc-cccc-cccc-cccc-cccccccccccc"
$workspaceLocation = "westeurope"

#Configure Version 1 Flow Logs
Set-AzNetworkWatcherConfigFlowLog -NetworkWatcher $NW -TargetResourceId $nsg.Id -StorageAccountId $storageAccount.Id -EnableFlowLog $true -FormatType Json -FormatVersion 1

#Configure Version 2 Flow Logs, and configure Traffic Analytics
Set-AzNetworkWatcherConfigFlowLog -NetworkWatcher $NW -TargetResourceId $nsg.Id -StorageAccountId $storageAccount.Id -EnableFlowLog $true -FormatType Json -FormatVersion 2

#Configure Version 2 FLow Logs with Traffic Analytics Configured
Set-AzNetworkWatcherConfigFlowLog -NetworkWatcher $NW -TargetResourceId $nsg.Id -StorageAccountId $storageAccount.Id -EnableFlowLog $true -FormatType Json -FormatVersion 2 -EnableTrafficAnalytics -WorkspaceResourceId $workspaceResourceId -WorkspaceGUID $workspaceid -WorkspaceLocation $workspaceRegion

#Query Flow Log Status
Get-AzNetworkWatcherFlowLogStatus -NetworkWatcher $NW -TargetResourceId $nsg.Id

The storage account you specify cannot have network rules configured for it that restrict network access to only Microsoft services or specific virtual networks. The storage account can be in the same, or a different Azure subscription, than the NSG that you enable the flow log for. If you use different subscriptions, they must both be associated to the same Azure Active Directory tenant. The account you use for each subscription must have the necessary permissions.

Disable Traffic Analytics and Network Security Group Flow logs

Use the following example to disable traffic analytics and flow logs:

#Disable Traffic Analaytics by removing -EnableTrafficAnalytics property
Set-AzNetworkWatcherConfigFlowLog -NetworkWatcher $NW -TargetResourceId $nsg.Id -StorageAccountId $storageAccount.Id -EnableFlowLog $true -FormatType Json -FormatVersion 2 -WorkspaceResourceId $workspaceResourceId -WorkspaceGUID $workspaceGUID -WorkspaceLocation $workspaceLocation

#Disable Flow Logging
Set-AzNetworkWatcherConfigFlowLog -NetworkWatcher $NW -TargetResourceId $nsg.Id -StorageAccountId $storageAccount.Id -EnableFlowLog $false

Download a Flow log

The storage location of a flow log is defined at creation. A convenient tool to access these flow logs saved to a storage account is Microsoft Azure Storage Explorer, which can be downloaded here: https://storageexplorer.com/

If a storage account is specified, flow log files are saved to a storage account at the following location:

https://{storageAccountName}.blob.core.windows.net/insights-logs-networksecuritygroupflowevent/resourceId=/SUBSCRIPTIONS/{subscriptionID}/RESOURCEGROUPS/{resourceGroupName}/PROVIDERS/MICROSOFT.NETWORK/NETWORKSECURITYGROUPS/{nsgName}/y={year}/m={month}/d={day}/h={hour}/m=00/macAddress={macAddress}/PT1H.json

For information about the structure of the log visit Network Security Group Flow log Overview

Next Steps

Learn how to Visualize your NSG flow logs with PowerBI

Learn how to Visualize your NSG flow logs with open source tools