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Objective : Demonstrate the ability to plan network segmentation to include IP address management and variable length subnetting. Discussion: Network Segmentation A broadcast domain is a logical division of a computer network where all nodes can reach every other node with a Layer 2 (data link layer) broadcast message. From a Layer 3 perspective, a broadcast domain is a logical division of the network a) that shares a subnet, b) shares a default gateway, and c) where all nodes can be reached with a L3 broadcast message. Yes, there are broadcast messages for both Layer 2 and Layer 3. Network design requires the ability to identify broadcast domains, or to determine where devices should be installed to create broadcast domains, and understanding how to allocate IP address space to those broadcast domains through subnetting. Subnetting Globally, there is a shortage of publicly routable IP addresses. Each publicly routable address can only be used by a single node at any given time. However, there are i mportant constraints on exactly where IP addresses can be used. IP addresses must be used in networks that are composed of sequential IP addresses. Classful networking is constructed around Class A, B and C networks and does not permit the division of netw orks into smaller subnets. Classful networking results in the waste of IP addresses, and is not used in modern networks. Classless networking uses subnet masks to divide classful networks into smaller subnets, enabling much greater efficiency in the use of available IP addresses. An additional nuance exists to classless subnetting. Variable Length Subnet Masks (VLSM) allows a network to have subnets of varying sizes, and is critical to ensuring the most efficient use of IPv4 addresses. VLSM is the standard practice in enterprise networks. The use of VLSM can introduce problems if network design is not done purposefully and carefully. A common problem is the introduction of overlapping addresses. Overlapping addresses is when two or more broadcast domains of varying size are assigned subnets where one or more IP addresses are assigned to multiple broadcast domains. For example, a /23 subnet is composed of two /24 subnets. If an organization assigned a /23 subnet to broadcast domain A, and one of the two /24 su bnets from that /23 subnet to broadcast domain B, the addresses in broadcast domain B would overlap with broadcast domain A. This creates routing problems. Therefore, overlapping subnets should be avoided. Additional factors for IP addressing that should b e considered during network planning include reserving spacing for expansion, the efficient use of IP addresses and how routes will be learned and shared. This project exposes you to IP address allocation through a practical exercise. Your organization is planning the network for a new branch operation that includes a main branch campus and a satellite location. The satellite campus is connected to the main campus by a site -to-site VPN. This branch is part of a larger enterprise network. IP addresses are co ntrolled centrally. Your branch has been allocated the address range 172.18.0.0 - 172.18.7.255. You are tasked with allocating IP address space to the network segments shown in Figure 1. Develop and submit a subnet plan that meets the requirements describ ed below. Figure 1, Branch Network Topology Resources : 1. Visio 2. Visio Stencil. Download with the lab instructions. Requirements : 1. Ensure subnets do not overlap. For each subnet, identify: a. Subnet ID b. Subnet mask c. First usable IP d. Last usable IP e. Broadcast IP 2. Table 1 identifies the immediate need for IP addresses in each network segment. Provide enough addresses to meet those immediate needs. 3. Identify the total number of spare IP addresses in each network segment. 4. Assume links between routing devic es (routers and firewalls) are point -to-point. In other words, only two assignable IP addresses are required and should be used on the links between routing devices. 5. Consolidate as many IP addresses as possible into a sequential set. Identify the starting and ending IP addresses of that set. Table 1, Network Segment Details Network Segment Nodes Comments DMZ 76 Admin Dept 88 Main LAN 650 Main Printers 47 Satellite LAN 180 Satellite Printers 24 Routing Links 2 Do not use IP addresses within a subnet that are designated as reserved by IANA Submission: 1. Submit a subnet plan that meets the identified requirements. 2. Identify the reserved subnet(s). 3. Identify spare IP addresses in allocated subnets.