The OSI model is the mannequin that almost all networking personnel are familiar with, however to earn your CCNA, you should know the OSI mannequin, the TCP/IP mannequin, and how the two map to each other. The four layers of the TCP/IP architecture could be in comparison with certain ranges of the OSI model. It's vital to know what every stage of the TCP/IP protocol structure does, and how these layers map to the OSI model. The Software Layer of the TCP/IP mannequin performs a lot the same duties because the Utility, Presentation, and Session layers of the OSI model. The Transport layer in the TCP/IP structure is much like the Transport layer within the OSI model. This layer can use TCP or UDP as well. The Internetwork layer within the TCP/IP architecture uses IP addresses to determine how packets ought to be routed. Keep in mind that the OSI model uses IP addresses, or "Layer 3 Addresses", on the Network layer. The two layers do much the same thing. This layer can also be referred to in the TCP/IP mannequin as the Web layer. The Community Interface layer in the TCP/IP architecture serves to outline the protocols and the hardware needed to truly ship the data across the network. The Network Interface mannequin does the work of both the Information Hyperlink and Physical Layers in the OSI model. Preserving all this straight can be very confusing once you first start your CCNA studies. Consider the OSI model in your research, however make sure you understand how the TCP/IP mannequin maps to that mannequin and you will be prepared for CCNA exam success! It'd occur in your CCNA examination, it'd happen in your manufacturing community - however in the end, you're going to must carry out password restoration on a Cisco router or switch. This entails manipulating the router's configuration register, and that is sufficient to make some CCNA candidates and community administrators really nervous! It is true that setting the configuration register to the wrong value can injury the router, however for those who do the correct analysis before starting the password recovery course of, you will be fine. Regardless of what some books say, there is no "one measurement suits all" method to Cisco password recovery. What works on a 2500 router could not work on different routers and switches. There's a great master Cisco doc out on the Internet that you must bookmark today. Simply put "cisco password recovery" in your favourite search engine and you must discover it quickly. The following process describes the method in recovering from a misplaced password on a Cisco 2500 router. As at all times, do not practice this at home. It's a good idea to get some practice with this technique in your CCNA / CCNP house lab, although! The password restoration method examined here is for 2500 routers. An engineer who finds themselves locked out of a router can view and change the password by altering the configuration register. The router should first be rebooted and a "break" performed within the first 60 seconds of the boot process. This break sequence may fluctuate depending on what program is used to access the router, but is the same old key combination. The router will now be in ROM Monitor mode. From the rom monitor immediate, change the default configuration register of 0x2102 to 0x2142 with the o/r 0x2142 command. Reload the router with the letter i. (As you may see, ROM Monitor mode is rather a lot completely different than working with the IOS!) This specific config register setting will trigger the router to disregard the contents of NVRAM. Your startup configuration is still there, however will probably be ignored on reload. When the router reloads, you'll be prompted to enter Setup mode. Reply "N", and kind allow on the router> prompt. Be careful here. Kind configure memory or copy start run. Do NOT kind write reminiscence or copy run start! Enter the command present working-config. You'll see the passwords in both their encrypted or unencrypted format. Type config t, then use the suitable command to set a brand new allow secret or allow password. Don't forget to change the configuration register setting again to the original value! The command config-register 0x2102 will do the job. Save this change with write reminiscence or copy run begin, and then run reload yet another time to restart the router. This course of sounds arduous, but it's actually not. You just have to be careful, notably whenever you're copying the startup config over the operating config. You do not wish to get that backwards! So take your time, examine the web Cisco documentation earlier than starting, get some follow with this procedure with lab gear, and you'll be ready for fulfillment on the CCNA examination and in your manufacturing network
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Mapping the OSI model to the TCP/IP model is a vital skill for CCNA examination success. Learn the details of each fashions from Chris Bryant, CCIE 12933.
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