Find-FreeSubnets freezes when there are multiple address spaces

[KasperKornak]

Hi David,

I have virtual network with two address spaces added to it. One with standard, private space, the second is an address range that is globally routable. Before adding the second address space, the command worked flawlessly, however it changed once the second space appeared. Right now, when running the standard Find-FreeSubnets command:

$result = Find-FreeSubnets -ResourceGroup my_rg -VNetName my_vnet

it's stuck and I get timeouts after 3 hours of inactivity in Automation Workbooks (same thing happens on my local PC, timeout excluded 😄).
Once ran with -Debug parameter, I can see that the command stops at GetAzureVirtualNetworkCommand, after all network resources are fetched correctly from Azure:

DEBUG: 16:15:25 - [ConfigManager] Got nothing from [DisplaySecretsWarning], Module = [], Cmdlet = []. Returning default value [True].
DEBUG: 16:15:25 - [ConfigManager] Got nothing from [DisplayRegionIdentified], Module = [], Cmdlet = []. Returning default value [True].
DEBUG: 16:15:25 - [ConfigManager] Got nothing from [CheckForUpgrade], Module = [], Cmdlet = []. Returning default value [True].
DEBUG: AzureQoSEvent:  Module: Az.Network:7.5.0; CommandName: Get-AzVirtualNetwork; PSVersion: 7.2.9; IsSuccess: True; Duration: 00:00:00.6666852; SanitizeDuration: 00:00:00.0001089
DEBUG: 16:15:25 - [ConfigManager] Got nothing from [EnableDataCollection], Module = [], Cmdlet = []. Returning default value [True].
DEBUG: 16:15:25 - GetAzureVirtualNetworkCommand end processing.

Could you consider investigating the issue?

Best regards,
Kasper

[flcdrg]

Thanks for the debug logging!

Can you try calling Get-AzVirtualNetwork yourself with the equivalent parameters to see if that also hangs?

[KasperKornak]

Hi David,

Maybe I described what happens in the wrong way - Get-AzVirtualNetwork -ResourceGroupName my_rg -Name my_vnet works correctly, and I can successfully get all resources from Azure. It seems that the mechanism which is responsible for finding available free subnets cannot process the data with the new address space.

[flcdrg]

I'm having trouble replicating this. Are you able to extract out the ARM/Bicep for the VNET/Subnet/Routing tables you're using?

I've not used 'globally routable' subnets before. Is this with a custom route table that routes to the Internet like this?

[KasperKornak]

Hi David,

Sorry for getting back to you so late - I was away with no access to computer. Can't really export the Arm/Bicep template as this wouldn't comply with security guidelines within my company. Below, you may find an example output of Get-AzVirtualNetwork -ResourceGroupName my_rg -Name my_vnet | Format-List * command with modified and shortened contents, which, on high level, shows set-up similar to ours.

You may see two address spaces attached to one Virtual Network and two subnets - each using different address space. If you have any more questions, please reach out to me.

AddressSpace                : Microsoft.Azure.Commands.Network.Models.PSAddressSpace
DhcpOptions                 : Microsoft.Azure.Commands.Network.Models.PSDhcpOptions
FlowTimeoutInMinutes        : 
Subnets                     : {snet_1, snet_2}
BgpCommunities              : 
Encryption                  : 
VirtualNetworkPeerings      : {VNET_PEERING_1}
ProvisioningState           : Succeeded
EnableDdosProtection        : False
DdosProtectionPlan          : 
IpAllocations               : {}
ExtendedLocation            : 
PrivateEndpointVNetPolicies : Disabled
AddressSpaceText            : {
                                "AddressPrefixes": [
                                  "10.0.0.0/21",
                                  "69.68.67.66/27"
                                ],
                                "IpamPoolPrefixAllocations": []
                              }
DhcpOptionsText             : {
                                "DnsServers": [
                                  "10.1.2.3",
                                  "10.1.2.4"
                                ]
                              }
FlowTimeoutInMinutesText    : null
SubnetsText                 : [
                                {
                                  "Delegations": [],
                                  "Name": "snet_1",
                                  "Etag": "W/\"xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx\"",
                                  "Id": "/subscriptions/yyyyyyyy-yyyy-yyyy-yyyy-yyyyyyyyyyyy/resourceGroups/rg1/providers/Microsoft.Network/virtualNetworks/VNET_1/subnets/snet_1",
                                  "AddressPrefix": [
                                    "10.0.0.0/27"
                                  ],
                                  "IpamPoolPrefixAllocations": [],
                                  "IpConfigurations": [],
                                  "ServiceAssociationLinks": [],
                                  "ResourceNavigationLinks": [],
                                  "ServiceEndpoints": [
                                    {
                                      "ProvisioningState": "Succeeded",
                                      "Service": "Microsoft.Storage",
                                      "Locations": [
                                        "westeurope"
                                      ]
                                    }
                                  ],
                                  "ServiceEndpointPolicies": [],
                                  "PrivateEndpoints": [],
                                  "ProvisioningState": "Succeeded",
                                  "PrivateEndpointNetworkPolicies": "Enabled",
                                  "PrivateLinkServiceNetworkPolicies": "Enabled",
                                  "IpAllocations": []
                                },
                                {
                                  "Delegations": [],
                                  "Name": "snet_2",
                                  "Etag": "W/\"xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx\"",
                                  "Id": "/subscriptions/yyyyyyyy-yyyy-yyyy-yyyy-yyyyyyyyyyyy/resourceGroups/rg1/providers/Microsoft.Network/virtualNetworks/VNET_1/subnets/snet_2",
                                  "AddressPrefix": [
                                    "69.68.67.66/29"
                                  ],
                                  "IpamPoolPrefixAllocations": [],
                                  "IpConfigurations": [
                                    {
                                      "Id": "/subscriptions/yyyyyyyy-yyyy-yyyy-yyyy-yyyyyyyyyyyy/resourceGroups/rg_2/providers/Microsoft.Network/loadBalancers/ilb_1/frontendIPConfigurations/ip_1"
                                    }
                                  ],
                                  "ServiceAssociationLinks": [],
                                  "ResourceNavigationLinks": [],
                                  "NetworkSecurityGroup": {
                                    "Id": "/subscriptions/yyyyyyyy-yyyy-yyyy-yyyy-yyyyyyyyyyyy/resourceGroups/rg1/providers/Microsoft.Network/networkSecurityGroups/snet_2_nsg"
                                  },
                                  "RouteTable": {
                                    "DisableBgpRoutePropagation": false,
                                    "Id": "/subscriptions/yyyyyyyy-yyyy-yyyy-yyyy-yyyyyyyyyyyy/resourceGroups/rg1/providers/Microsoft.Network/routeTables/route_table_1"
                                  },
                                  "ServiceEndpoints": [
                                    {
                                      "ProvisioningState": "Succeeded",
                                      "Service": "Microsoft.Storage",
                                      "Locations": [
                                        "westeurope"
                                      ]
                                    }
                                  ],
                                  "ServiceEndpointPolicies": [],
                                  "PrivateEndpoints": [],
                                  "ProvisioningState": "Succeeded",
                                  "PrivateEndpointNetworkPolicies": "Enabled",
                                  "PrivateLinkServiceNetworkPolicies": "Enabled",
                                  "IpAllocations": [],
                                  "DefaultOutboundAccess": true
                                }
                              ]
BgpCommunitiesText          : null
EncryptionText              : null