Routers by Albert Zenuni Adrian Sifuentes Victor Ponce Pontea Nadar Jordan Kao Information Systems 311 Professor Gray Table of Contents Introduction 1 Information Economy 3 Router Types 4 Home Routers 4 Small Organization and Office Routers 5 High End Routers 6 Notable Issues 14 Routing Algorithms 15 Flooding the Network 16 Adding Complexity 16 Types of Routing 17 Centralized Routing 17 Decentralized Routing 17 Static Routing 17 Dynamic Routing 17 Introduction Routers have become ubiquitous in the world of networking computing Without routers transporting data across computers would be very limited if not impossible But what exactly is routing Routing is the process that allows data to travel from location to location Moreover it is the process of determining the route or path through the network that a message will travel from the sending computer to the receiving computer It is the technology that has been largely responsible for allowing the Internet to work Today s networks are large masses of routers located throughout the world and maintained by governments private enterprise non profit organizations and other entities Routers work by taking data in the form of e mail web browser requests and file transfers and delivering these data items to their appropriate destinations More specifically routers work by reading the contents of data packets in the aforementioned data formats and determining the correct source and destination for the packet The router can also discover the best way to get the packet to its destination The Internet itself is a large network comprised of interconnected routers In this case routers take requests from their local users and forward those requests to the appropriate server With the advent of the Internet and network computing routers have become essential in today s interconnected world Without routers every computer would have to be connected together and every user would need to know the address of every website they wanted to visit as well as the computers you would need to pass through to get there With the interconnectivity available to us today sending data is an easy task For example to reach a specific web site a user enters a URL address in a web browser such as Microsoft Internet Explorer or Netscape Navigator CSUN s URL address for example is http www csun edu The following scenario occurs to transmit the message The browser sends a message to the Internet service provider s ISP routers The message notifies router that you want to see the information stored at www csun edu The routers then translate the URL address to 130 166 1 55 CSUN s IP address and send the request to the routers that service this address 1 The request then travels to the ISP s routers Each router examines the request determines which IP address is being requested and which address is the requester and matches the information against its own routing table routing tables are discussed later in this document The routing table tells it where to find the IP address being requested If the routing table doesn t contain that information it will know the address of another router to forward the request to This process continues until the request finally reaches www csun edu With this example the routing tables would keep track of who made the request and then send the information back to the user There are many ways to describe and analyze data communications networks All networks provide the same basic functions to transfer a message from sender to receiver but each network can use different network hardware and software to provide these functions All of these hardware and software products have to work together to successfully transfer a message A common approach to accomplish this is to break down the set of communications functions into a series of layers each defined separately This is beneficial for vendors who can then develop the hardware and software for each particular layer Network layers can be designed in a number of ways One of the most important network models is the Open Systems Interconnection Reference OSI The OSI has seven layers Figure 1 1 1 Physical Layer Primarily concerned with transmitting data bits over a communication circuit 2 Data Link Layer Manages the physical transmission circuit and converts it into a circuit that is free of transmission errors 3 Network Layer Performs routing 4 Transport Layer Deals with end to end issues 5 Session Layer Responsible for initiating maintaining and ending each logical session between end users 6 Presentation Layer Formats the data for presentation to the user 7 Application Layer the end user s entrance to the network 2 Figure 1 2 Data is created at the Application layer and makes it way down through each layer As it passes through each layer it may add header or a trailer see Figure 2 This is known as encapsulation Each lower layer treats the complete packet including the header from the top layer as data In other words it does not concern itself with the encapsulation of the top layers Figure 2 1 3 Information Economy Networking is influenced from the shift toward an information based business economy and the Internet Organizations have learned to adapt to this shift and now realize that information must be stored retrieved manipulated and shared within their organizations as well as others Several common devices are used to connect these network segments Routers will be the focus of discussion Routers operate at the network layer Its purpose is to connect two or more network segments that use the same or different data link protocols but the same network protocol Additionally they may connect the same or different types of cable Routers strip off the data link layer packet and process the network layer packet They forward only those messages that need to go to other networks on the basis of their network layer address Router Types Routers may come in a plethora of types including black boxes computers with several network interface cards or special network modules in computers or other devices Manufacturers of routers include Cisco Routers 3Com D Link IBM Intel Nortel Networks and Juniper Each one of these manufacturers creates different kinds of routers that can be used for various reasons Routers can be used to connect computers together in an office environment In another instance backbone routers are use to support large organizations and small businesses Routers come in different sizes For example