![]() ![]() The first thing you decided to do was draw a high-level network diagram indicating each branch, which shows the number of hosts per branch office and the Wide Area Network (WAN) links between each branch router:Īs we can see from the preceding diagram, each building has a branch router, and each router is connected to another using a WAN link. He has also told you to use an address class that is suitable for the company’s size and to ensure that there is minimal wastage of IP addresses. The task is to redesign the IP scheme of the company. Let’s assume that you are a network administrator at a local company and one day the IT manager assigns a new task to you. This brings us to other questions, such as why do we need to break down a single IP address block, and why is least wastage so important? Could we simply assign a Class A, B, or C address block to a network of any size? To answer these questions, we will go more in depth with this topic by using practical examples and scenarios. Second, the reason we need to subnet is to efficiently distribute IP addresses with the result of less wastage. What is subnetting and why do we need to subnet a network?įirst, subnetting is the process of breaking down a single IP address block into smaller subnetworks (subnets). The private address space is divided into three classes: Class A- 10.0.0.0/8 network block Most ISPs usually have a filter to prevent any private addresses (RFC 1918) from entering their network. This means that if a device is directly connected to the internet with a private IPv4 address, there will be no network connectivity to devices on the internet. However, on the internet, the public IPv4 address is unique to a device. ![]() They can be used within an organization or a private network. The benefit of using the private address space (RFC 1918) is that the classes are not unique to any particular organization or group. This means within a private network such as LAN. Private IPv4 addressesĪs defined by RFC 1918, there are three classes of private IPv4 address that are allocated for private use only. Therefore, all of the devices on the internet will see the public IPv4 address and not the sender’s actual IP address. For any devices that are behind the internet gateway that want to communicate with another device on the internet, NAT will translate the sender’s source IP address to the public IPv4 address. The internet gateway or router is usually configured with Network Addresses Translation (NAT), which is the method of mapping either a group of IP addresses or a single IP address on the internet-facing interface to the local area network (LAN). If ISPs give their customers a single public IPv4 address on their modem or router, how can this single public IPv4 address serve more than one device from within the organization or home? So, what about the devices that require internet access from within the organization or home? There may be a few devices to hundreds or even thousands of devices that require an internet connection and an IP address to communicate to the internet from within a company. However, in a lot of organizations and homes, only one public IPv4 address is assigned to the router or modem’s publicly facing interface. The following diagram shows how a public IP address is seen by internet users: As mentioned earlier, there are approximately four billion public IPv4 addresses. On the internet, classes A, B, and C are commonly used on devices that are directly connected to the internet, such as layer 3 switches, routers, firewalls, servers, and any other network-related device. Class E addresses are reserved for experimental usage and are not assignable. Class D addresses are used for multicast traffic. ![]()
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