ccna security 640-554 book

ccna security 640-554 book.VLSM enables you to use different subnet masks in a classified address space (Class A, Class B, or Class C networks). Classification protocols (such as Routing Information Protocol (RIP) version 1) do not support VLSMo to use VLSM, you must use a classless routing protocol in your network, such as Border Gateway Protocol (BGP), Enhanced Interior Gateway Routing Protocol (EIGRP), Intermediate System Intermediate System (1S-IS). Open Shortest Path First (OSPF), RIPv2oVLSM has two main advantages as follows.. Efficient use of addresses in large networks .. Ability to perform route aggregation (route aggregation) and thus reduce the size of routing tables in routers.Exam Essentials VLSM gives you the ability to use multiple subnet masks within a single classified address space. Keep in mind the two main benefits of VLSM: more efficient use of addresses; and support for route aggregation/aggregation.As these benefits point out, VLSM allows you to make more efficient use of IP addresses. Figure 7.1 is a simple example that illustrates the situation before and after using VLSM. In this example, a router at the company headquarters (Router A) is connected to routers at remote offices (Router B, Router C, and Router D) via a point-to-point WAN linkChapter 7 VLSM 141LANs at these remote sites have approximately 50 devices (hence the use of subnet masks/26). Before using VLSM, a uniform subnet mask is used throughout the network - 255.255.255.192, which allows each subnet to contain up to 62 hosts. Based on the number of segments the network contains, two Class C networks are required. In a WAN segment, this would waste a lot of addressing space, since only two host addresses are required for a point-to-point link.Router BIn the lower part of Figure 7.1, the address space is used more efficiently by using VLSM. In this example, the subnet mask 255.255.255.192o is used at the three remote sites, but in the last subnet (192.168.1.192/26), a different subnet mask is used to further divide it into multiple subnets and assign them to WAN point-to-point connections. By using this VLSM solution, only one Class C network is required to meet the addressing needs of this network.The second benefit of VLANs (route summarization) is discussed later in this chapter.How should you use subnet 0 when implementing VLSM? There are two different views on this. One view prefers to further divide subnet 0 into multiple subnets. This is popular when some operating systems do not necessarily support subnet 0, but network devices such as routers do. Another view is that this is not a problem at this time, since all modern TCP/IP stacks (including those for desktops, laptops, and mobile devices) support subnet Oo