Protect your network

Securing your network from attacks and unauthorized access is an important part of any architecture. Here, we'll take a look at what network security looks like, how to integrate a layered approach into your architecture, and how Azure can help you provide network security for your environment.

A layered approach to network security

You've probably noticed that a common theme throughout this module is the emphasis of a layered approach to security. This approach is also recommended at the network layer. It's not enough to just focus on securing the network perimeter, or focusing on the network security between services inside a network. A layered approach provides multiple levels of protection, so that if an attacker gets through one layer, there are further protections in place to limit further attack.

Let's take a look at how Azure can provide the tools for a layered approach to securing your network footprint.

Internet protection

If we start on the perimeter of the network, we're focused on limiting and eliminating attacks from the internet. We suggest first assessing the resources that are internet-facing, and to only allow inbound and outbound communication where necessary. Make sure you identify all resources that are allowing inbound network traffic of any type, and then ensure they are restricted to only the ports and protocols required. Azure Security Center is a great place to look for this information, because it will identify internet-facing resources that don't have network security groups associated with them, as well as resources that are not secured behind a firewall.

What is a Firewall?

A firewall is a service that grants server access based on the originating IP address of each request. You create firewall rules that specify ranges of IP addresses. Only clients from these granted IP addresses will be allowed to access the server. Firewall rules, generally speaking, also include specific network protocol and port information.

To provide inbound protection at the perimeter, you have several choices.

  • Azure Firewall is a managed, cloud-based, network security service that protects your Azure Virtual Network resources. It is a fully stateful firewall as a service with built-in high availability and unrestricted cloud scalability. Azure Firewall provides inbound protection for non-HTTP/S protocols. Examples of non-HTTP/S protocols include: Remote Desktop Protocol (RDP), Secure Shell (SSH), and File Transfer Protocol (FTP). It also provides outbound, network-level protection for all ports and protocols, and application-level protection for outbound HTTP/S.

  • Azure Application Gateway is a load balancer that includes a Web Application Firewall (WAF) that provides protection from common, known vulnerabilities in websites. It is designed to protect HTTP traffic.

  • Network virtual appliances (NVAs) are ideal options for non-HTTP services or advanced configurations, and are similar to hardware firewall appliances.

Stopping Distributed Denial of Service (DDoS) attacks

Any resource exposed on the internet is at risk of being attacked by a denial of service attack. These types of attacks attempt to overwhelm a network resource by sending so many requests that the resource becomes slow or unresponsive.

When you combine Azure DDoS Protection with application design best practices, you help provide defense against DDoS attacks. DDoS Protection leverages the scale and elasticity of Microsoft's global network to bring DDoS mitigation capacity to every Azure region. The Azure DDoS Protection service protects your Azure applications by monitoring traffic at the Azure network edge before it can impact your service's availability. Within a few minutes of attack detection, you are notified using Azure Monitor metrics.

This diagram shows network traffic flowing into Azure from both customers and an attacker. Azure DDoS protection identifies the attacker's attempt to overwhelm the network and blocks further traffic from reaching Azure services. Legitimate traffic from customers still flows into Azure without any interruption of service.

Illustration showing Azure DDoS protection installed between virtual network and external user requests. The Azure DDoS protection blocks malicious traffic attack but forwards legitimate traffic to the intended destination.

Azure DDoS Protection provides the following service tiers:

  • Basic - The Basic service tier is automatically enabled as part of the Azure platform. Always-on traffic monitoring and real-time mitigation of common network-level attacks provide the same defenses that Microsoft's online services use. Azure's global network is used to distribute and mitigate attack traffic across regions.
  • Standard - The Standard service tier provides additional mitigation capabilities that are tuned specifically to Microsoft Azure Virtual Network resources. DDoS Protection Standard is simple to enable and requires no application changes. Protection policies are tuned through dedicated traffic monitoring and machine learning algorithms. Policies are applied to public IP addresses associated with resources deployed in virtual networks, such as Azure Load Balancer and Application Gateway. DDoS standard protection can mitigate the following types of attacks:
    • Volumetric attacks. The attackers goal is to flood the network layer with a substantial amount of seemingly legitimate traffic.
    • Protocol attacks. These attacks render a target inaccessible, by exploiting a weakness in the layer 3 and layer 4 protocol stack.
    • Resource (application) layer attacks. These attacks target web application packets to disrupt the transmission of data between hosts.

Controlling the traffic inside your virtual network

Virtual network security

Once inside a virtual network (VNet), it's crucial that you limit communication between resources to only what is required.

For communication between virtual machines, Network Security Groups (NSGs) are a critical piece to restrict unnecessary communication.

Network Security Groups allow you to filter network traffic to and from Azure resources in an Azure virtual network. An NSG can contain multiple inbound and outbound security rules that enable you to filter traffic to and from resources by source and destination IP address, port, and protocol. They provide a list of allowed and denied communication to and from network interfaces and subnets, and are fully customizable.

You can completely remove public internet access to your services by restricting access to service endpoints. With service endpoints, Azure service access can be limited to your virtual network.

Network integration

It's common to have existing network infrastructure that needs to be integrated to provide communication from on-premises networks or to provide improved communication between services in Azure. There are a few key ways to handle this integration and improve the security of your network.

Virtual private network (VPN) connections are a common way of establishing secure communication channels between networks. Connections between Azure Virtual Network and an on-premises VPN device are a great way to provide secure communication between your network and your VNet on Azure.

To provide a dedicated, private connection between your network and Azure, you can use Azure ExpressRoute. ExpressRoute lets you extend your on-premises networks into the Microsoft cloud over a private connection facilitated by a connectivity provider. With ExpressRoute, you can establish connections to Microsoft cloud services, such as Microsoft Azure, Office 365, and Dynamics 365. ExpressRoute connections improve the security of your on-premises communication by sending this traffic over the private circuit instead of over the public internet. You don't need to allow access to these services for your end users over the public internet, and you can send this traffic through appliances for further traffic inspection.

Summary

A layered approach to network security helps reduce your risk of exposure through network-based attacks. Azure provides several services and capabilities to secure your internet-facing resource, internal resources, and communication between on-premises networks. These features make it possible to create secure solutions on Azure.

You can also combine multiple Azure networking and security services to manage your network security and provide increased layered protection. For example, you can use Azure Firewall to protect inbound and outbound traffic to the Internet, and Network Security Groups to limit traffic to resources inside your virtual networks.