Configuring Network Security Group Flow logs with Azure PowerShell

Article
01/20/2023
2 minutes to read

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.

The detailed specification of all NSG flow logs commands for various versions of AzPowerShell can be found here

Note

The commands Get-AzNetworkWatcherFlowLogStatus and Set-AzNetworkWatcherConfigFlowLog used in this doc, requires an additional "reader" permission in the resource group of the network watcher. Also, these commands are old and may soon be deprecated.
It is recommended to use the new Get-AzNetworkWatcherFlowLog and Set-AzNetworkWatcherFlowLog commands instead.
The new Get-AzNetworkWatcherFlowLog command offers four variants for flexibility. In case you are using the "Location <String>" variant of this command, an additional "reader" permission in the resource group of the network watcher would be required. For other variants, no additional permissions are required.

Register Insights provider

In order for flow logging to work successfully, the Microsoft.Insights provider must be registered. If you aren't 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 $workspaceGUID -WorkspaceLocation $workspaceLocation

#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 with 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 Analytics 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 Power BI

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