Router Chassis Types
| Cisco manufactures a wide range of router products that spans the small home office to Internet core routers. After you get beyond a small basic router that would be useful in a small home office, routers tend to become more configurablefrom a hardware perspective. That is, they are modular, and different models can be adapted to different environments by installing interface cards to match your needs. Additionally, all but the smallest routers come in rack-mounted versions so that you don't have to dedicate a large amount of valuable office space to them. No matter what size your LAN or network is, it's a bet that Cisco has a router solution for you. At the high end of the market are routers capable of serving as Internet core routers. These are the high-bandwidth routers that your local ISP or other large-scale provider uses to connect to the Internet backbone. Such routers allow for line cards that allow them to connect to high-speed fiber-optic links, as well as cards that allow for connections to more typical 100BASE-T networks. In addition to Cisco, other router vendors also offer a full range of products. At the high end of the market, however, the competition isn't so great. One vendor, Juniper Networks, markets only high-end routers. This company makes routers that are intended for very large networks and network backbone uses. For example, Juniper's M10i routers can route and forward network packets at 12.8Gbps (gigabits per second!) in full-duplex mode. Juniper's routers can be configured with various physical interface cards (PICs), each of which contains different network interfaces, ranging from simple 10BASE-T Ethernet connections up to OC-192c/STM-64 optical fiber link connections. The high-end M320 router (shown in Figure 10.5) is intended to serve as either an Internet core router or a very flexible, configurable high-end router for a large network backbone. Figure 10.5. The Juniper M320 is a high-end Internet backbone router. Photo courtesy of Juniper Networks. In Figure 10.6, you can see one of the PIC modules you can use with M-series routers. This figure shows a simple Gigabit Ethernet module. Figure 10.6. This PIC module enables M-series routers to connect to a Gigabit Ethernet link. Photo courtesy of Juniper Networks. By carefully choosing the modules you add to a high-end router, it is possible to aggregate smaller links, such as those provided by ISDN or T-carrier lines, into high-speed connections to the Internet. The fact that you can always change out modules to accommodate a changing network infrastructure helps justify the cost of these high-end routers. Juniper, Cisco, and other manufacturers produce various types of highly configurable high-end routers. However, most users of this book will be dealing with low-end to medium-sized networks, and will find that they don't have to spend a lot of time configuring or managing a router if you set it up correctly in the first place. If you work with an ISP and use a high-end router, plan to spend a lot of time with the manuals. For small offices, a multitude of vendors make router/switch combinations that can be used to connect using dial-up or broadband (cable/DSL) to the Internet and other remote networks.
Using Routers over Wide Area Networks (WANs)You can create a wide area network (WAN) by purchasing your own set of leased linesan expensive proposition for many smaller companiesor you can connect your network to the Internet and take your chances there. Using a good router that provides for packet filtering and Virtual Private Networks (VPNs), you can effectively tunnel your network traffic through the Internet in encrypted form. Connecting each branch office, you might find that using DSL technologies is much cheaper than using a more expensive ISDN dial-up or T1 dedicated line. Instead, because you'll have a larger amount of traffic bound to and from the company's headquarters, you can install a large pipe at that point and use cheaper methods out in the field, spending the money for a large data pipe only where it is needed: at the central headquarters. If you choose to connect a business network to the Internet, you must be familiar with firewall technology. This means you must be familiar with the specific model of router used in your organization. Cisco is perhaps the most widely known brand of routers, but for small offices there exist many viable and inexpensive choices. Besides packet filtering and NAT that are generally supported by most routers, you also should investigate using proxy servers to further isolate your network from the rest of the world.
Routers and the InternetIt should be obvious that without routers it would be almost impossible to consider the connection of millions of computers such as has been accomplished with the proliferation of the Internet. In the first place, the topological restrictions placed on Ethernet, Token-Ring, and other transport protocols would limit the size to which the network could grow. Second, if routing were not done using a logical addressing scheme, any device that connects a network to another network would have to keep a table in memory that consists of all nodes on all networks to which it is connected! Although computing power has been increasing at extremely fast rates in the past few years, it's doubtful that anyone could devise a machine that could keep track of all the computers in the world and efficiently route a large number of packets to their correct destinations. The routing table would be so large that it would take forever to route packets. Instead, all a router must do is know the address of a network, or the address of another router that knows how to deliver packets to the destination network. If you use the tracert command in Windows (or traceroute in Unix and Linux) to trace the route a packet takes to a particular website, you'll most likely see that it goes through many routers before it reaches its destination. For example: G:\>tracert www.bd-studios.com Tracing route to www.bd-studios.com [207.213.224.83] over a maximum of 30 hops: 1 140 ms 150 ms 150 ms envlnjewsap01.bellatlantic.net Clearly, connecting to another computer on the Internet isn't always such a simple thing! High-speed lines and fast, efficient core routers can make it seem (if you are using a fast, digital connection) as if all the servers you access are just around the corner from you. Instead, they could be on the opposite side of the world. Another interesting thing to note about routers is that packets that are part of the same original communication can take different routes to get to the eventual destination. Routing tables change constantly, and what might be a good route at one moment might not be the next. For this reason, higher-level protocols, such as TCP, take care of the mechanics involved in determining whether packets are received and reassembled into the correct order. |
[192.168.125.173] 2 * 140 ms * 192.168.125.158 3 140 ms 150 ms 151 ms 206.125.199.71 4 140 ms 150 ms 150 ms 205.171.37.13 5 140 ms 151 ms 150 ms jfk-core-01.inet.qwest.net [205.171.30.85] 6 150 ms * 150 ms wdc-core-02.inet.qwest.net [205.171.5.235] 7 150 ms 160 ms 160 ms wdc-core-03.inet.qwest.net [205.171.24.6] 8 180 ms 180 ms 180 ms hou-core-01.inet.qwest.net [205.171.5.187] 9 180 ms 190 ms 191 ms dal-core-02.inet.qwest.net [205.171.5.172] 10 180 ms 191 ms 190 ms dal-brdr-02.inet.qwest.net [205.171.25.50] 11 180 ms 190 ms 190 ms 39.ATM1-0.BR1.DFW9.ALTER.NET [137.39.23.217] 12 180 ms 191 ms 190 ms 140.at-6-0-0.XR1.DFW9.ALTER.NET [152.63.98.126] 13 181 ms * 180 ms 185.at-1-0-0.TR1.DFW9.ALTER.NET [152.63.98.26] 14 220 ms 231 ms 230 ms 128.at-5-1-0.TR1.LAX9.ALTER.NET [152.63.3.162] 15 221 ms 230 ms 220 ms 297.ATM7-0.XR1.LAX4.ALTER.NET [152.63.112.181] 16 220 ms 230 ms 231 ms 193.ATM6-0.GW4.LAX4.ALTER.NET [152.63.113.89] 17 * 220 ms 230 ms savvis-lax2.customer.alter.net 
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