IPv4 and IPv6 Addresses
For details, refer to:
Understand IP addresses
A simplified explanation of IP addresses is to compare them to phone numbers: all computers connected directly to the internet have a unique "phone number." These numbers are called IP addresses.
IPv4 and IPv6 addresses look like these examples:
IPv4: 192.0.2.10, 098.51.100.252, 203.0.113.123
IPv6: 2001:db8:0a0b:12f0:0000:0000
Note
In our documentation, we use example IPv4 addresses and subnets reserved for documentation, such as 192.0.2.0/24, 198.51.100.0/24, and 203.0.113.0/24.
Ensure you replace them with valid IPv4 addresses and subnets for your network(s).
Note
The IPv6 address 2001:db8 used in our examples is reserved for documentation use.
Replace it with a valid IPv6 address for your network.
Each IP address must be unique. For IPv4 addresses, numbers can range from 0 to 255. With 256 to the fourth power, you get an amazing 4294967296 possible IP addresses. That's a lot, but we have a lot of devices on the internet.
Access Server focuses on IPv4 addresses because they are simpler to grasp and work with while still offering enough possibilities.
IPv6 addresses provide more possible addresses. Currently, the internet uses a mix of IPv4 and IPv6. Access Server also limitedly supports IPv6 traffic in the OpenVPN tunnel.
NAT and IP addresses
Network address translation (NAT) provides firewall protection and internal network access using one internet IP address for all devices. Your business network is considered private, and devices are not directly accessible online. With NAT, a single router device at the head of the network has one public internet IP address and manages your private network with internal private IP addresses.
For more about NAT and how Access Server uses it for routing, click this topic: NAT and Routing.
CIDR and subnet masks
These are two methods of notation for IP routes. When working with a routing table, which is basically a list of IP addresses and where to send traffic, it's rather impractical to name every IP address individually. So, instead, we use subnet ranges.
An example subnet can be 192.0.2.0/24. That is CIDR notation and means to say: all addresses starting at 192.0.2.0 and ending with 192.0.2.255. So, an address like 192.0.2.222 or 192.0.2.4 would fall within that subnet. The equivalent of this range notation with a subnet mask instead would look like 192.0.20 255.255.255.0. The method of writing it down is different, but it means the same thing: the same range from 192.0.2.0 all the way to 192.0.2.255. There are large and small subnets; the larger a subnet is, the lower the mask or CIDR number is. The other way around, the smaller a subnet is, the more specific it is, and the higher the number on CIDR or subnet mask is. There is a mathematical logic behind calculating the subnet mask or CIDR number, but for ease of use, we recommend referring to a subnet mask cheat sheet if you need to convert one to the other.