NVA Part III: NVA Redundancy – Connection from the Internet

This chapter is the first part of a series on Azure's highly available Network Virtual Appliance (NVA) solutions. It explains how we can use load balancers to achieve active/active NVA redundancy for connections initiated from the Internet.

In Figure 4-1, Virtual Machine (VM) vm-prod-1 uses the load balancer's Frontend IP address 20.240.9.27 to publish an application (SSH connection) to the Internet. Vm-prod-1 is located behind an active/active NVA FW cluster. Vm-prod-1 and NVAs have vNICs attached to the subnet 10.0.2.0/24.

Both NVAs have identical Pre- and Post-routing policies. If the ingress packet's destination IP address is 20.240.9.27 (load balancer's Frontend IP) and the transport layer protocol is TCP, the policy changes the destination IP address to 10.0.2.6 (vm-prod-1). Additionally, before routing the packet through the Ethernet 1 interface, the Post-routing policy replaces the original source IP with the IP address of the egress interface Eth1.

The second vNICs of the NVAs are connected to the subnet 10.0.1.0/24. We have associated these vNICs with the load balancer's backend pool. The Inbound rule binds the Frontend IP address to the Backend pool and defines the load-sharing policies. In our example, the packets of SSH connections from the remote host to the Frontend IP are distributed between NVA1 and NVA2. Moreover, an Inbound rule determines the Health Probe policy associated with the Inbound rule.

Note! Using a single VNet design eliminates the need to define static routes in the subnet-specific route table and the VM's Linux kernel. This solution is suitable for small-scale implementations. However, the Hub-and-Spoke VNet topology offers simplified network management, enhanced security, scalability, performance, and hybrid connectivity. I will explain how to achieve NVA redundancy in the Hub-and-Spoke VNet topology in upcoming chapters.

Figure 4-1: Example Diagram. 

NVA Part II - Internet Access with a single NVA

Introduction

In the previous chapter, you learned how to route east-west traffic through the Network Virtual Appliance (NVA) using subnet-specific route tables with User Defined Routes (UDR). This chapter introduces how to route north-south traffic between the Internet and your Azure Virtual Network through the NVA.

Figure 3-1 depicts our VNet setup, which includes DMZ and Web Tier zones. The NVA, vm-nva-fw, is connected to subnet snet-north (10.0.2.0/24) in the DMZ via a vNIC with Direct IP (DIP) 10.0.2.4. We've also assigned a public IP address, 51.12.90.63, to this vNIC. The second vNIC is connected to subnet snet-west (10.0.0.0/24) in the Web Tier, with DIP 10.0.0.5. We have enabled IP Forwarding in both vNICs and Linux kernel. We are using Network Security Groups (NSGs) for filtering north-south traffic.

Our web server, vm-west, has a vNIC with DIP 10.0.0.4 that is connected to the subnet snet-west in the Web Tier. We have associated the route table to the subnet with the UDR, which forwards traffic to destination IP 141.192.166.81 (remote host) to NVA. To publish the web server to the internet, we've used the public IP of NVA. 

On the NVA, we have configured a Destination NAT rule which rewrites the destination IP address to 10.0.0.4 to packets with the source IP address 141.192.166.81 and protocol ICMP. To simulate an http connection, we're using ICMP requests from a remote host.

Figure 3-1: Example Diagram and.