Understanding IP addressing and DNS in Azure – Network Connectivity and Security
When building services in Azure, you sometimes choose to use internal IP addresses and external IP addresses. Internal IP addresses can only communicate internally and use VNETs. Many services can also use public IP addresses, which allow you to communicate with the service from the internet.
Before we delve into public and internal IP addresses, we need to understand the basics of IP addressing in general, and especially the use of subnets and subnet masks.
Understanding subnets and subnet masks
When devices are connected to a TCP/IP-based network, they are provided with an IP address in the notation xxx.xxx.xxx.xxx. Generally, all devices that are on the same local network can communicate with each other without any additional settings.
When devices on different networks need to communicate, they must do so via a router or gateway. Devices use a subnet mask to differentiate between addresses on the local network and those on a remote network.
The network mask breaks down an IP address into a device or host address component and a network component. It does this by laying a binary mask over the IP address with the host address to the right.
255 in binary is 11111111 and 0 in binary is 00000000. The mask says how many of those bits are the network, with 1 denoting a network address and 0 denoting a host address.
Thus, 255.0.0.0 becomes 11111111.00000000.00000000.0000000, therefore in the address 10.0.0.1, 10 is the network and 0.0.0.1 is the host address. Similarly, with a mask of 255.255.0.0 and an address of 10.0.0.1, 10.0 becomes the network and 0.1 the host. The following diagram shows this concept more clearly:
Figure 8.1 – Example subnet mask
Splitting an address space into multiple networks is known as subnetting, and subnets can be broken down into even smaller subnets until the mask becomes too big.
When configuring IP settings for devices, you often supply an IP address, a subnet mask, and the address of the router on the local network that will connect you to other networks.
Sometimes, when denoting an IP address range, the subnet mask and range are written in a shorthand form known as CIDR notation. We will cover CIDR notation examples in the Private IP addresses sub-section.
This is a relatively simplified overview of network addressing and subnetting, and although the AZ-304 exam will not explicitly ask you questions on this, it does help to better understand the next set of topics.