Migrate to Standard IP - GatewaySubnet does not have sufficient IP Addresses available.

Question

Migrate to Standard IP - GatewaySubnet does not have sufficient IP Addresses available.

Amah James 20

New to Azure. Inherited environment. Received Microsoft notifications that Action required: Migrate your VPN Gateway to Standard Public IP. Attempting the migration using the GUI interface. Validation - Failed. Please take action on the failed resources to resolve.

AddressPrefix Name PrivateEndpoints ProvisioningState PrivateEndpointNetworkPolicies PrivateLinkServiceNetworkPolicies PrivateEndpointsText

{10.96.53.248/29} GatewaySubnet {} Succeeded Enabled Enabled []

{10.96.52.0/24} AZE-Internal {} Succeeded Enabled Enabled []

{10.96.53.0/25} AZE-External {} Succeeded Enabled Enabled []

The subnet is too small . I know the subnet needs to be resized, but worry about effecting production while trying to resize it.

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Answer 1

Marcin Policht 109.5K MVP Volunteer Moderator

You can't modify a subnet if there are any resources attached to it - as per https://learn.microsoft.com/bs-latn-ba/azure/virtual-network/virtual-network-manage-subnet?tabs=azure-portal#change-subnet-settings

This means you effectively have two primary options:

provision a new VNET with GatewaySubnet of increased size - you can potentially designate it as a "hub" vnet and peer to the existing one (and delete the gateway/GatewaySubnet from it)
delete the gateway, recreate GatewaySubnet and redeploy the gateway. A rough timeline should be actually acceptable from the business impact perspective - assuming you're not operating 24/7 - just consider that the public IP address will be changing. More at https://community.spiceworks.com/t/resize-vnet-gatewaysubnet-in-azure/633626

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin

Amah James 20 Reputation points

2026-06-23T22:54:31.36+00:00

Thanks for your response Marcin. It seems like the first option you outlined is actually what is detailed here https://learn.microsoft.com/en-us/azure/virtual-network/how-to-multiple-prefixes-subnet?tabs=powershell, is this what you were eluding to?
Marcin Policht 109.5K Reputation points MVP Volunteer Moderator

2026-06-23T23:24:04.6733333+00:00

Actually no - the issue (as I understand it) is not the inability to extend the current IP address space in the VNet, but rather the inherent limitation of subnets, which cannot be extended as long as there are resources connected to them. So you can either delete the gateway to remove that limitation (and extend the subnet afterwards, either by using the existing IP address space of the VNet or potentially adding an extra prefix - which is what the article you referenced is describing) - or create a completely new VNet and use it to host the gateway. The second option is not particularly appealing (because it forces you to redesign your existing VNet architecture and/or migrate resources from the original VNet) - so I'd consider it only if you cannot afford the downtime necessary to redeploy the gateway when using the first option

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin