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When not at work patching network cables into routers and hubs for a local newspaper, Danny shared his home with his aged father and his demure, unassuming sister, Annie
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Those mail routers are persistent if nothing else
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When not at work patching network cables into routers and
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Routers and servers around them
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routers that may be required by the team
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when you’re in front of a rack of routers and switches during a job interview (or at 2AM
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still not Cisco routers, and they never will be
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You do your best learning not only when you’re configuring your routers, but when you
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There are several vendors that sell routers and switches on ebay most of them sell CCNA
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What isn't as immediately apparent is why we use loopback interfaces on routers and
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The password recovery method examined here is for 2500 routers
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The problem is that one of the routers needs to act as the DCE in order for the line
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In this example, though, we don't have physical access to the routers
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Cisco routers and switches, and that's TFTP - Trivial File Transfer Protocol
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Cisco routers can themselves serve as TFTP servers, or you can use a workstation
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We have two routers (R2 and R3) along with two switches (SW1 and SW2)
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routers have IP addresses on the 172
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For these routers to be able to ping each other, the switches must be able to
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this is the only thing the wireless routers do, they don't usually need any
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It's probably worth noting here that the Linksys routers are the most popular
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routers out there, and it's the easiest to use out of the lot
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Wireless routers are designed to work easily out of the box: in most cases, it
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Most routers support PPPoE, but you'll have to read the manual and do some
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Wireless routers generally solve more problems than they cause -- but there are
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Wireless routers have built-in firewalls
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be expensive, though -- prices are roughly similar to wireless routers
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With routers and access points, one thing that might work is to log in to their
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MIPS continues to supply some SGI systems, but is primarily used as an embedded design, notably in Cisco routers
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Network hardware The cables, routers, bridges, firewalls, and software that enable computers to connect to shared printers, databases, and each other
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It’s a closed system, with its own routers, portals and bridges, and it’s completely separate from the rest of the Internet
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• The ability to route orders to an exchange: You need to know that “smart routers” are in fact smart, just not in the way they are presented to the general public
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• Routers A router is a device that connects two LANs to form an internetwork
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Like a bridge, a router forwards only the traffic that is destined for the connected segment, but unlike repeaters and bridges, routers do not forward broadcast messages
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Routers can also connect different types of networks (such as Ethernet and Token Ring), whereas bridges and repeaters can connect only segments of the same type
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A typical WAN connection consists of two routers, one at each LAN site, connected using a long-distance link such as a leased telephone line
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Bridges have mainly been replaced by routers and switches, which are covered later in this chapter
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Routers are more selective than bridges in the traffic they pass between the networks, and they are capable of intelligently selecting the most efficient path to a specific destination
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Because they function at the network layer, routers can also connect dissimilar networks
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Most Windows systems today function as routers as well
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Whether wired or wireless, network routers work at the network layer of the OSI model
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Most of the routers used on large networks, though, are stand-alone devices that are essentially computers dedicated to routing functions
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Routers come in various sizes, from small units that connect a workgroup network to a backbone to large, modular, rack-mounted devices
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However, while routers vary in their capabilities, such as the number of networks to which they connect, the protocols they support, and the amount of traffic they can handle, their basic functions are essentially the same
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Figure 4-8 Wired and wireless routers enable the use of wide area connections to join two LANs
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To make communications between the networks in the two offices possible, each must connect its LAN to a router, and the two routers are linked by the WAN connection
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Here, routers are needed because one single LAN may be unable to support the number of workstations required
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Routers are available that can connect these different network types, no matter what protocols they use
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Figure 4-9 A hierarchy of routers helps you forward traffic to any location using the Internet
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A packet can pass through several different routers on the way to its destination
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On the Internet, a packet can easily pass through 20 or more routers along its path
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Figure 4-11 Routers have direct knowledge about the networks to which they are connected
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When a network is larger and uses multiple routers, however, no single router has direct knowledge of all the LANs
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How then does Router A know where to send packets that are addressed to a workstation on a distant network? The answer is that routers maintain information in their routing tables about other networks besides those to which they are directly attached
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On the Internet, however, there are so many networks and so many routers that no single routing table can contain all of them and function efficiently
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Instead, these networks use dynamic routing, in which specialized routing protocols share information about the other routers in the network and modify the routing tables accordingly
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Many networks, even relatively small ones, are designed with multiple routers that provide redundant paths to a given destination
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Thus, while creating a network that consists of several LANs joined in a series by routers would be possible, most use something approaching a mesh topology instead, as shown in Figure 4-14
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Figure 4-14 By interconnecting routers, packets from one computer can travel to a destination computer on another network on a different route
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If, for any reason, the packet passes through routers enough times to bring the value of this field down to 0, the last router removes it from the network and discards it
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Routers can connect networks of vastly different types, and the process of transferring datagrams from one data link layer protocol to another can require more than simply stripping off one header and applying a new one
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The Internet Control Message Protocol provides several important functions to routers and the systems that use them
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Chief among these is the capability of routers to use ICMP messages to provide routing information to other routers
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Routers send ICMP redirect messages to source systems when they know of a better route than the system is currently using
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Routers also generate ICMP Destination Unreachable messages of various types when they are unable to forward packets
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ICMP is therefore a mechanism that enables intermediate systems (routers) to communicate with a source end system (the transmitter) in the event that the packets can’t reach the destination end system
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Other ICMP packets, called Router Solicitation and Advertisement messages, can enable workstations to discover the routers on the local network
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A host system generates a Router Solicitation message and transmits it as either a broadcast or a multicast to the All Routers on This Subnet address (2240
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Routers receiving the message respond with Router Advertisement messages that the host system uses to update its routing table
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The routers then generate periodic updates to inform the host of their continued operational status
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Routers that support dynamic routing use specialized protocols to exchange information about themselves with other routers on the network
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Private networks typically use only interior gateway protocols because they have a relatively small number of routers and it is practical for all of them to exchange messages with each other
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The routers within an AS use an interior gateway protocol, such as the Routing Information Protocol (RIP) or the Open Shortest Path First (OSPF) protocol, to exchange routing information among themselves
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At the edges of an AS are routers that communicate with the other autonomous systems on the Internet, using an exterior gateway protocol, the most common of which on the Internet are the Border Gateway Protocol (BC-P) and the Exterior Gateway Protocol (EGP)
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By splitting the routing chores into a two-level hierarchy, packets traveling across the Internet pass through routers that contain only the information needed to get them to the right AS
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Once the packets arrive at the edge of the AS in which the destination system is located, the routers there contain more specific information about the networks within the AS
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The traditional network configuration uses multiple LANs connected by routers to form a network that is larger than would be possible with a single LAN
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Routers segregate the traffic on the individual LANs, forwarding only those packets addressed to systems on other LANs
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Routers have been around for decades, but today switches have revolutionized network design and made it possible to create LANs of almost unlimited size
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Figure 4-17 Today, hierarchies of switches replace both hubs and routers
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One of the advantages of creating multiple LANs and connecting them with routers is that broadcasts are limited to the individual networks
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Routers also provide security by limiting transmissions to a single subnet
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A virtual LAN (VLAN) is a group of systems on a switched network that functions as a subnet and communicates with other VLANs through routers
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Despite the fact that all the computers are connected by switches, routers are still necessary for systems in different VLANs to communicate
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By replacing the routers that connect workgroup or department networks to the backbone with layer 3 switches, you retain all of the router functionality, while increasing the overall speed at which data is forwarded
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Instead, horizontal cable runs can extend all the way from wall plates down to a central equipment room that contains all of the network’s patch panels, hubs, switches, routers, and other such devices
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Figure 7-1 Routers or bridges connect WAN links to LANs
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While bridges are always separate units, the routers used to connect two networks with a WAN link can take the form of either a computer or a dedicated hardware device
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Most sites use dedicated routers
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On a LAN, when you want to increase the bandwidth available to users, you can upgrade to a faster protocol or add network connection components such as bridges, switches, and routers
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You might have to limit the amount of traffic that passes over the link in ways other than just using routers at each end
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There are also stand-alone routers that perform in the same way, enabling users to connect to a remote LAN or the Internet as needed
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References to ATM systems and devices refer to switches and routers, as well as actual computers
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An ATM backbone, therefore, may be connected not only to data networking components such as routers, switches, and servers, but also to PBXs and other telecommunications devices
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The advantage of a collapsed backbone is that internetwork traffic has to pass through only one router on the way to its destination, unlike a distributed backbone, which has separate routers connecting each network to the backbone
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You can, for example, use two routers on each LAN, both of which connect to the backbone network hub so that if one router fails, the other provides continued access to the rest of the network
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For example, you can purchase Fast Ethernet hubs and routers that support both cable types so that you can use UTP on your horizontal networks and fiber optic on the backbone
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The center typically contains the network’s enterprise servers and the routers that join the LANs together and provide Internet and WAN access
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Because of its use as a backbone protocol, products such as bridges and routers that connect Ethernet networks to FDDI backbones are common
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Routers use the network bits to forward packets to another router connected to the destination network, which then transmits the data to the destination host system
