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Routers An Overview

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The purpose of this paper is give a summary of the function and use of Routers in today's information age. To cover the complete subject of routers and routing, would be beyond the scope of this research paper. However the basic definition of a router is " A device used to connect networks of different types, such as those using different architectures and protocols. Routers work at the Network layer of the OSI model. This means they can switch and route packets across multiple networks. They do this by exchanging protocol-specific information between separate networks. Routers determine the best path for sending data and filter broadcast traffic to the local segment."

( Microsoft Press, 1998)


In order for information to pass fro one information system to another information system outside its local area it must be routed. In the below table is an illustration of a the route a data packet takes between my computer and the Web Server for Macon State College.

Tracing route to []

over a maximum of 30 hops:




1 <10 ms <10 ms <10 ms

2 <10 ms <10 ms <10 ms

3 <10 ms <10 ms 16 ms

4 <10 ms 15 ms 16 ms

5 15 ms 63 ms 16 ms

6 32 ms 47 ms 46 ms c7513.vldsgacbds0-1.Hssi2-0-0.near.ptp.optilinkc []

7 62 ms 47 ms 94 ms c7513.vldsgacbds0-1.ATM3-0-0-2.far.ptp.optilinkc []

8 78 ms 94 ms 78 ms Serial2-7.GW4.DCA1.ALTER.NET []

9 94 ms 62 ms 79 ms []

10 63 ms 94 ms 78 ms 195.ATM6-0.BR2.DCA1.ALTER.NET []

11 63 ms 94 ms 109 ms [205.


12 1938 ms 1859 ms 1891 ms [205.215.6


13 1859 ms 1907 ms 1875 ms

14 94 ms 94 ms 94 ms



15 78 ms 109 ms 94 ms

16 109 ms 94 ms 78 ms UD-MAC-MAC.Link.Peach.NET []

17 94 ms 94 ms 109 ms

18 94 ms 94 ms 109 ms []

As can be seen in the above table it took 18 hops or to reach, this is referred to as the Metric count. If you will examine metrics one through

five you will notice that it took five hops just to leave my local area network. It is amazing to follow the route and see that my packet went all the way to Washington D.C. before it arrived at Macon State's web server. All along the way decisions were made on how to route the packet based on it's IP address.

(Todd Lammle, 1998)

A I.P address is a logical 32-bit address used to identify a IP host. Each IP address has two parts: the network ID and the Host ID. The network Id identifies all hosts that are on the same physical network. For example, in Table 1, you can see that the first IP address was, that is the address of my default router. My router took a look at (the IP of the Macon State Web Server) and new it was not on the local network. It then sent it across it's Wan link ( to it's default router


5 Then router looks at the package and recognizes it is not for it's local network, send it to which is a multi-homed NT firewall. The firewall accepts the protocol and allows the packet to leave the border router to begin it's journey to the Macon State Web site. All this happens in time that is measured in Milliseconds.

( Matthew Rees, 1999)

Routers build what are known as routing tables as they pass packets along. These tables contain the information that allows a router to look at destination address and make a decision on where to forward that packet. The majority of routing tables are built using dynamic protocols, which learn routes from neighboring routers. However for security purposes an administrator may build static routing tables. This can be a time consuming process and may be prone to errors or failures if a route changes. Some examples of routing



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