Work with hybrid networks on Azure

Your organization is eager to continue with migration to the cloud. You explored the merits of using Azure ExpressRoute to provide a dedicated, high-speed connection between your on-premises network and Azure.

Due diligence requires you to explore the other available hybrid architecture options for connecting your on-premises network to Azure.

In this unit, you will:

• Gain an understanding of virtual private network connections.
• Look at a resiliency option for ExpressRoute.
• Consider the merits of hub-spoke network topology.

What is a hybrid network architecture?

Hybrid network is a term used when two different network topologies combine to form a single cohesive network. With Azure, a hybrid network represents the merging or combining of an on-premises network with an Azure virtual network. It allows the continued use of your existing infrastructure while giving you all the benefits of cloud-based computing and access.

There are several reasons why you might want to adopt a hybrid network solution. The two most common are:

• To migrate from a pure on-premises network to a pure cloud-based network.
• To extend your on-premises network and resources to support the cloud services.

Whatever your motivations for adding cloud services to your infrastructure, there are several architectures to consider. We covered ExpressRoute in the preceding unit. The other architectures are:

• Azure VPN Gateway
• ExpressRoute with VPN failover
• Hub-spoke network topology

Azure VPN Gateway

Azure VPN Gateway, a virtual network gateway service, allows site-to-site and point-to-site VPN connectivity between your on-premises network and Azure.

A VPN or virtual private network is a well-established, well-understood network architecture.

VPN Gateway uses your existing connection to the internet. However, all communication is encrypted using the Internet Key Exchange (IKE) and Internet Protocol Security (IPsec) protocols. You can have only one virtual network gateway per virtual network.

When you set up a virtual network gateway, you must specify whether it's a VPN gateway or an ExpressRoute gateway.

The VPN type depends on the type of connection topology you need. For example, if you want to create a point-to-site (P2S) or a point-to-point (P2P) gateway, you use a RouteBased type. There are two VPN types:

• PolicyBased: Uses an IPsec tunnel to encrypt data packets. Configuration of the policy uses address prefixes drawn from your Azure virtual network and your on-premises network.
• RouteBased: Uses the routing or IP forwarding tables to route data packets to the correct tunnel. Each tunnel encrypts and decrypts all packets.

After you specify the VPN type for the virtual network gateway, you can't alter it. If you have to make a change, delete the virtual network gateway and create it again.

Site-to-site

All site-to-site gateway connections use an IPsec/IKE VPN tunnel to create a connection between Azure and your on-premises network. A site-to-site connection requires an on-premises VPN device with a publicly accessible IP address.

Point-to-site

A point-to-site gateway connection creates a secured connection between an individual device and your Azure virtual network. This gateway type is suited to remote workers; for example, users attending a conference or working from home. A point-to-site connection doesn't require a dedicated on-premises VPN device.

Benefits

Here are some of the benefits of using a VPN connection:

• It's a well-known technology, easy to configure and maintain.
• All data traffic is encrypted.
• It's better for handling lighter data-traffic loads.

Considerations

When you're evaluating the use of this hybrid architecture, consider the following points:

• A VPN connection uses the internet.
• Potential latency issues might exist, depending on bandwidth size and usage.
• Azure supports a maximum bandwidth of 1.25 Gbps.
• A local VPN device is needed for site-to-site connections.

ExpressRoute with VPN failover

One of the guarantees of using ExpressRoute is that it provides a high level of availability. Each ExpressRoute circuit comes with dual ExpressRoute gateways. However, even with this level of resiliency built into the Azure side of the network, connectivity might be interrupted. One way to remedy this situation, and maintain connectivity, is to provide a VPN failover service.

The merging of the VPN connection and ExpressRoute improves the resiliency of your network connection. When it operates under normal conditions, ExpressRoute behaves precisely like a regular ExpressRoute architecture, with the VPN connection remaining dormant. If the ExpressRoute circuit fails or goes offline, the VPN connection takes over. This action ensures network availability under all circumstances. When the ExpressRoute circuit is restored, all traffic reverts to using the ExpressRoute connection.

Reference architecture for ExpressRoute with VPN failover

The following diagram illustrates how to connect your on-premises network to Azure by using ExpressRoute with a VPN failover. The chosen topology in this solution is a VPN-based, site-to-site connection with high traffic flow.

In this model, all network traffic routes through the ExpressRoute private connection. When connectivity is lost on the ExpressRoute circuit, the gateway subnet automatically fails over to the site-to-site VPN gateway circuit. The dotted line from the gateway to the VPN gateway in the Azure virtual network indicates this scenario.

When the ExpressRoute circuit is restored, traffic automatically switches back from the VPN gateway.

Benefits

The following benefit is available when you implement ExpressRoute with a VPN failover:

• It creates a resilient, high availability network.

Considerations

When you implement an ExpressRoute with VPN failover architecture, consider the following points:

• When a failover occurs, bandwidth is reduced to VPN connection speeds.

• The ExpressRoute and VPN gateway resources must be in the same virtual network.

• There's a highly complex configuration.

• Implementation requires both an ExpressRoute connection and a VPN connection.

• Implementation requires a redundant VPN gateway and local VPN hardware.

  Note

  A redundant VPN gateway incurs payment charges, even when it's not being used.

Hub-spoke network topology

The hub-spoke network topology allows you to structure the workloads that your servers carry out. It uses a single virtual network as the hub, which connects to your on-premises network through either VPN or ExpressRoute. The spokes are other virtual networks that are peered with the hub. You can assign specific workloads to each spoke, and use the hub for shared services.

You can implement the hub and each spoke in separate subscriptions or resource groups and then peer them together.

This model uses one of the three previously discussed approaches: VPN, ExpressRoute, and ExpressRoute with VPN failover. The associated benefits and challenges are discussed in the following sections.

Benefits

Implementing a hub-spoke architecture has the following benefits:

• The use of sharing and centralized services on the hub might reduce the need for duplication on the spokes, which can reduce costs.
• Subscription limits are overcome by peering virtual networks.
• The hub-spoke model allows for the separation of organizational work areas into dedicated spokes, such as SecOps, InfraOps, and DevOps.

Considerations

When you're evaluating the use of this hybrid architecture, consider the following point:

• Look at the services that are shared on the hub and what remains on the spokes.