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INFS 3700

by: berbaroot

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About this Document

Notes on Routers for the first week.
Morgan Shepherd
Class Notes
Routers, networks, InformstionSystems
25 ?




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Popular in 3700

This 3 page Class Notes was uploaded by berbaroot on Thursday May 19, 2016. The Class Notes belongs to infs at University of Colorado Colorado Springs taught by Morgan Shepherd in Fall 2015. Since its upload, it has received 10 views. For similar materials see Networks in 3700 at University of Colorado Colorado Springs.


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Date Created: 05/19/16
Barbara Root 08/31/2015 Routers  Specialized networking device connected to 2 or more networks, running software that allows the router to more data from one network to another  Functions in an Internet protocol based network operate at the network layer  Primary function of router is to connect networks together and keep certain types of broadcast traffic under control  Router companies consist of : Cisco, Linksys, Juniper, Netgear, Belkin, HP How do routers work? EX: Home wireless router connected to a cable provider's internet network 1. The router powers on and loads it's OS from flash 2. The router loads the configuration file last saved to NVRAM and sets up the network interfaces and routing protocols it will run. 3. The router adds the network address and subnet for each interface to it's routing table along with the name of the interface itself. 4. The router has a simple static default route to send all non-local data out the network port connected to the cable company. 5. When the router receives a web page request from your computer, it checks the destination IP address against its routing table. 6. The bits forming the destination IP address in the IP packet are used as a hash key to point to the correct route, which in turn points to the correct network interface that the packet should be forwarded out of. 7. The router transmits the packet out the correct interface, to the next router, which repeats the process until the packet reaches the destination.  The process is mostly the same for any router. For home cable and Wi-Fi routers, the router is also acting as a "proxy" so the router does one thing that is NOT normal for a router out on the Internet some where: it changes the source IP address in the IP packet to its own address Functions of a Router 1. Restrict broadcasts to the LAN i. Network broadcast communication is used to communicate certain kinds of information that makes the network function ii. Several devices could attempt to transmit simultaneously and cause collisions; it is preferable to separate large sets of hosts into different broadcast domains using a switch, or router. iii. As the number of hosts on the network increases, the amount of broadcast traffic increases iv. To reduce broadcasts, a network administrator can break up a network with a large number of hosts into two smaller networks. v. Broadcasts are then restricted to each network, and the router performs as the 'default gateway' to reach the hosts on the other networks. 2. Act as the default gateway i. When your computer wants to talk to a computer on another network, it does so by sending your data to the default gateway. Barbara Root 08/31/2015 ii. Default gateway is the local router connected to the same network your computer is connected to. iii. The router serving as the default gateway receives your data, looks for the remote address of that far-off computer and makes a routing decision. iv. Based on that routing decision, it forwards your data out a different interface that is closer to that remote computer. v. There could be several routers between you and the remote computer, so several routers will take part in handing off the packet, much like a fireman's bucket brigade. – 3. Move (route) Data between Networks i. Routers have the capability to move data from one network to another. ii. This allows two networks managed by different organizations to exchange data. iii. They create a network between them and exchange data between the routers on that network. Because a router can accept traffic from any kind of network it is attached to, and forward it to any other network, it can also allow networks that could not normally communicate with each other to exchange data. 4. Learn and Advertise Loop-Free Paths i. Routers can only learn and advertise routes dynamically if they are using a routing protocol. Otherwise, a human has to configure the routes by hand, which is called static routing. ii. Routing moves data on a hop-by-hop basis, what is often called 'hot potato' routing. iii. If a set of routers ends up passing the data around in a circle, without reaching the destination, it's called a 'routing loop'. iv. Packets get handed off around the loop until they die of old age: their 'Time To Live' expires. Time To Live is a counter that is part of the IP datagram header. v. The Time To Live value is decremented as it passes through each router and eventually it reaches zero and is discarded. Router Components & Parts  Since routers are just specialized computers, the have the same "parts" as other computers:  Central Processing Unit (CPU)  Flash Memory  Non-Volatile RAM  RAM  Network Interfaces  Console Central Processing Unit: Runs special software called an "operating system" such as JunOS on Juniper routers, or Cisco IOS (Nexus OS) for Cisco routers. The operating system manages the router's components and provides all the logical networking functions of the router. Barbara Root 08/31/2015 Flash Memory is where the operating system is stored, and in this respect, is like the hard disk drive in your computer. If you use a Solid State Disk Drive (SSD), then your computer uses Flash RAM, just like the router does. Non-Volatile RAM: This is additional memory for storing the backup or startup version of the operating system being used. The router will boot from this memory and load all its programs from here. RAM: When the router starts up, the operating system is loaded into RAM. Once the router finishes starting up, it begins to calculate its own routes and, if configured to do so, learns network routes from other routers via RIP (v1 and v2), OSPF, EIGRP, IS- IS or BGP. RAM is also used for caching ARP tables, routing tables, routing metrics and other data that can speed up the process of forwarding of packets. Network Interfaces: Routers always have lots of network interfaces. The operating system contains 'drivers' that allow the operating system to access the network hardware in the interface modules. Routers will learn which networks are configured on which ports as they start up. After that, they will 'learn' routes from other routers they are connected to, and learn which interface to transmit packets on to reach a remote network destination. Console: Last, but not least, is the console. In "Ye Olden Days" managing and configuring a router was performed at the console of individual devices, as was most troubleshooting and diagnostics. Network certification exams will contain a large selection of questions on the configuration and troubleshooting commands you can issue from the console. However, manufacturers are rapidly doing away with a console on each device and building management systems for managing large numbers of network devices from a centralized location. - See more at: .faHqZGPY.dpuf


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