12/24/2022 0 Comments Cisco subnet mask table![]() ![]() The subnet mask is going to be used by hosts, to identify traffic that goes outside of their own subnet, and it is also going to be used by routers to identify networks and subnets and be able to forward traffic toward those destinations. Possible Subnets and Hosts for a Class C Network It is a measuring tool that tells you how far to look into the IP address to find the network piece, then the subnet piece, and then what is left is the host piece. This is a mask that serves as a pair of glasses to look at the addresses differently. In this context, then the mask is not similar to the Halloween masks that your kids may use. It is in the subnet mask, the one component that will tell us each section. In classless routing, the class of the address no longer tells us what portion of the address is network, subnet, or host. When we do this, we are talking about a classless environment. Telephone numbers make sense within a city, which has a city code and the cities are part of a country. This is a hierarchy that is similar to our telephone numbering system we have country codes and then city codes and then telephone numbers. We are dividing networks into subnets and then subnets contain hosts. We are going to have the network defined by the class, but also a subnet and also then the host. We are effectively creating a third leg of the hierarchy. When we subnet a classful IP address, what we are doing is stealing bits from the host portion of the address and then making them part of the subnet portion of the address. How can we tell which portion of the IP address is the network and which portion is the host? In classful routing, the class would tell us which bytes are dedicated to the network ID and which bytes are dedicated to the host. A denial of service attack may not reach other subnets if the router is acting as some sort of a firewall in the middle, regardless of the reason for subneting when we do we need to assign each subnet a different network or subnet ID and then hosts within that subnet would have a unique host ID portion of the IP address. If something happens on one subnet, then the effect is mitigated even by the router in other subnets.Įxamples are also related to security. The router would be a policy in force or at that point, because it controls traffic from one subnet to the other, here also isolating network problems. Also, you compartmentalize the network and then you can apply different polices to the different compartments. You are breaking things into smaller pieces and this divide-and-conquer approach will make things easier to manage. With the segmentation like this in multiple subnets, overall traffic is reduced, each subnet is a broadcast domain and, therefore, broadcasts coming from engineering in this example would not touch manufacturing.Ī router effectively stops local broadcasts however, there are more advantages with the subnetting. The advantages are not only on the performance side. Routers can be used in these scenarios to break the network into multiple broadcast domains or subnets. The more machines you add, and more devices you add, the more performance degradation you are going to experience. MAC addresses have no hierarchical structure and we are still talking about a flat network. ![]() A logical segment is a broadcast domain and so all the devices in a flat topology would share the same broadcast domain and all of them would see each others’ broadcasts affecting performance and throughput in the network. The only intelligence in filter mechanism would be a layer 2 switch, which forwards based on MAC addresses. ![]() If we do not have routing, then we are talking about one flat network or flat topology where all devices belong to the same logical segment. The immediate thought is WAN and the Internet however, routing also makes sense in the campus network and even in smaller local area networks for the purposes of traffic segmentation. When talking about routing one tends to think about forwarding packets to remote destinations. You will actually get a chance to practice, subnet mask operations using class A, B, and C IP addresses. In doing so, we will describe the use of subnet masks, and how they are used by insistence and by routers. Using real-life examples we will describe the process of calculating sudden host addresses. We are going to describe classful and classless operations, including use of subnets. Our knowledge of binary numbers leads us directly into the structure of IP addresses, and best practices in allocating them. ![]()
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