CompTIA’s Network+ certification Study Guide part 27 is a globally-recognized, vendor neutral exam that has helped over 235,000 IT professionals reach further and higher in their careers. The 2009 Network+ exam (N10-004) is a major update with more focus on security and wireless aspects of networking. Our new study guide has been updated accordingly with focus on network, systems, and WAN security and complete coverage of today’s wireless networking standards. | 246 CHAPTER 6 The OSI Model and Networking Protocols TCP IP protocols on the Internet and the IPX addresses used by the IPX SPX protocols on NetWare networks are examples of logical addresses. These protocol stacks are referred to as routable because they include addressing schemes that identify both the network or subnet and the particular client on that network or subnet. Other network transport protocols such as NetBIOS Extended User Interface NetBEUI do not have a sophisticated addressing scheme nor the programming intelligence of high OSI model layers such as network and transport layers thus crippling it and not allowing it to be routed across different networks. To make sure you understand what is meant by this view Figure . Here you see a network subdivided by different IP subnets this will be covered in greater depth in Chapter 7 . You can see that each local area network LAN is connected to each other via a WAN using Frame Relay both of which will be covered in depth in Chapter 7 . The most critical fact here is that all of this logical addressing and routing are done at the network layer of the OSI model. Each subnet must be unique and each LAN will need to know how to get to the other LANs. That s where the WAN and the routers come in acting as the default gateway for your network. Also you need to understand that logical addressing such as the address being assigned to the router on the LAN as the default gateway is important it defines how and where the packets are sent and so on. So now that you have assigned the IP address how does the MAC address tie in Well a TCP IP protocol called Address Resolution Protocol ARP will help map an IP address to a physical machine address. Note To understand the difference between physical and logical addresses consider this analogy if you buy a house it has a physical address that identifies exactly where it is located on the earth at a specific latitude and longitude. This never changes .
