The Illustrated Network- P5:In this chapter, you will learn about the protocol stack used on the global public Internet and how these protocols have been evolving in today’s world. We’ll review some key basic defi nitions and see the network used to illustrate all of the examples in this book, as well as the packet content, the role that hosts and routers play on the network, and how graphic user and command line interfaces (GUI and CLI, respectively) both are used to interact with devices. | CHAPTER 1 Protocols and Layers 9 bsdclient ssh -l remote-user@CEO remote-user@ce0 s password --- JUNOS built 2007-08-06 06 58 15 UTC remote-user@CEO These examples show the conventions that will appear in this book when command-line procedures are shown. All prompts output and code listings appear like this. Whenever a user types a command to produce some output the command typed will appear like this. We ll see CLI examples from Windows hosts as well. Illustrated Network Router Roles The intermediate systems or network nodes used on the Illustrated Network are routers. Not all of the routers play the same role in the network and some have switching capabilities. The router s role depends on its position in the network. Generally smaller routers populate the edge of the network near the LANs and hosts while larger routers populate the ISP s network core. The routers on our network have one of three network-centric designations we have LAN switches also but these are not routers. Customer edge CE These two routers belong to us in our role as the customer who owns and operates the hosts and LANs. These CE routers are smaller than the other routers in terms of size number of ports and capabilities. Technically on this network they perform a gateway role. Provider edge PE These two routers gather the traffic from customers typically there are many CE routers of course . They are not usually accessible by customers. Provider P These six routers are arranged in what is often called a quad. The two service providers on the Illustrated Network each manage two providers routers in their network core. Quads make sure traffic flows smoothly even if any one router or one link fails on the provider s core networks. Ethernet LAN switches The network also contains two Ethernet LAN switches. We ll spend a lot of time exploring switches later. For now consider that switches operate on Layer 2 frames and routers operate on Layer 3 packets. Now what is this second example .
