Azure Virtual Network Gateway

Azure Virtual Network Gateway is the parent resource that can be configured to become a ExpressRoute Gateway, or VPN Gateway.

Both types of gateways require that a specific Azure Subnet must be deployed to the Azure Virtual Network, with the Exact Name of GatewaySubnet.
This subnet can be as small as /29, but it is recommended to be a /27 or larger to account for more ExpressRoute / VPN Connections.

When configuring a connection, a #Local Network Gateway and a #Connection are configured to represent a on-premises location.

VPN Gateway

Azure VPN Gateway is used to create a Virtual Private Network connections as either Point-to-Site, Site-to-Site or Vnet-to-Vnet to a Azure Virtual Network via IPSec.

Azure Resource Architecture

To connect a VPN to another network, several sub resources are deployed to store information.

• The on-premises network represents your on-premises Active Directory and any data or resources.
• The gateway is responsible for sending encrypted traffic to a virtual IP address when it uses a public connection.
• The Azure virtual network holds all your cloud applications and any Azure VPN gateway components.
• An Azure VPN gateway provides the encrypted link between the Azure virtual network and your on-premises network. An Azure VPN gateway is made up of these elements:
  • Virtual network gateway
  • Local network gateway
  • Connection
  • Gateway subnet
• Cloud applications are the ones you've made available through Azure.
• An internal load balancer, located in the front end, routes cloud traffic to the correct cloud-based application or resource.

VPN Gateway Types

VPN Gateway can be deployed as Policy Based or Route Based. This option can not be changed after the provisioning of the VPN Gateway.
Policy Based can only be used with basic SKU and are limited to IKEv1, while Route Based is the option for the other SKUs and supports IKEv2.
Microsoft recommendation is to use Route Based

SKUs

(*) Use Virtual WAN if you need more than 30 S2S VPN tunnels.

All the VPN SKUs can be actively resized at anytime, but the Basic SKU is a legacy SKU, and can not be resized.

Local Network Gateway

Connection

High Availability

To provide better availability for your VPN connections, there are a few options available:

• #VPN Gateway Redundancy
• #Multiple on-premises VPN devices
• #Active-active Azure VPN gateway
• Combination of both

VPN Gateway Redundancy

Every Azure VPN Gateway consists of two instances in a Active-standby configuration. Failover to the standby instance is automatically attempted for any planned maintenance or unplanned disruption.
Planned maintenance connectivity should typically be restored within 10-15 seconds, and unplanned disruption should be recovered in about 1-3 minutes. S2S connections should automatically reconnect, but P2S will likely need to be re initiated.

Multiple On-premises VPN Devices

This solution is used to create redundancy on the on-premises side of the configuration, but follows the same constraints as the #VPN Gateway Redundancy on the Azure side.
There are some requirements and constraints:

1. You need to create multiple S2S VPN connections from your VPN devices to Azure. When you connect multiple VPN devices from the same on-premises network to Azure, you need to create one local network gateway for each VPN device, and one connection from your Azure VPN gateway to each local network gateway.
2. The local network gateways corresponding to your VPN devices must have unique public IP addresses in the GatewayIpAddress property.
3. BGP is required for this configuration. Each local network gateway representing a VPN device must have a unique BGP peer IP address specified in the Bgp PeerIpAddress property.
4. You should use BGP to advertise the same prefixes of the same on-premises network prefixes to your Azure VPN gateway, and the traffic will be forwarded through these tunnels simultaneously.
5. You must use Equal-cost multi-path routing (ECMP).
6. Each connection is counted against the maximum number of tunnels for your Azure VPN gateway, 10 for Basic and Standard SKUs, and 30 for HighPerformance SKU.

Active-active Azure VPN Gateway

Note that both VPN tunnels are part of the same connection. You will still need to configure your on-premises VPN device to accept or establish two S2S VPN tunnels to those two Azure VPN gateway public IP addresses.
Because the Azure gateway instances are in active-active configuration, the traffic from your Azure virtual network to your on-premises network will be routed through both tunnels simultaneously, even if your on-premises VPN device may favour one tunnel over the other. For a single TCP or UDP flow, Azure attempts to use the same tunnel when sending packets to your on-premises network. However, your on-premises network could use a different tunnel to send packets to Azure.

Dual Redundant Active-Active

Here you create and set up the Azure VPN gateway in an active-active configuration and create two local network gateways and two connections for your two on-premises VPN devices as described above. The result is a full mesh connectivity of 4 IPsec tunnels between your Azure virtual network and your on-premises network.

Tips and Troubleshooting

Use Azure DNS Private Resolver over Azure VPN

Cant Route to Spoke from P2S

• General steps:
  • Check that the DNS Private Resolver is added to the VPN config
• If using a Azure Firewall and Forced Tunnelling:
  • Check that the routes for the VPN range on the spokes, not just a 0.0.0.0/0.
  • Check that the AzureFirewallSubnet has routes that route the subnet ranges to the Virtual Network Gateway.
  • Check that the VNG advertises the routes for the spokes.
  • Check that the Vnet peering is working.
  • Disable the Gateway Route propagation on the peering, as force tunnelling works around this.

Troubleshoot Azure VPN Gateway Using Diagnostic Logs

Using diagnostic logs, you can troubleshoot multiple VPN gateway related events including configuration activity, VPN Tunnel connectivity, IPsec logging, BGP route exchanges, Point to Site advanced logging.

There are several diagnostic logs you can use to help troubleshoot a problem with your VPN Gateway.

• GatewayDiagnosticLog - Contains diagnostic logs for gateway configuration events, primary changes, and maintenance events.
• TunnelDiagnosticLog - Contains tunnel state change events. Tunnel connect/disconnect events have a summarized reason for the state change if applicable.
• RouteDiagnosticLog - Logs changes to static routes and BGP events that occur on the gateway.
• IKEDiagnosticLog - Logs IKE control messages and events on the gateway.
• P2SDiagnosticLog - Logs point-to-site control messages and events on the gateway.

Use Azure Monitor to analyse the data collected in the diagnostic logs.

Express Route Gateway

An Virtual Network Gateway can be configured as a Azure ExpressRoute Gateway.