Troy’s checklist for preparing for the CCNA: Objective 4 – part 1

June 19, 2009 at 11:06 am | Posted in Cisco | Leave a comment
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Welcome to to this week’s exciting double feature. Today we’ll dive into what you need to know in Objective 4: Configure, verify, and troubleshoot basic router operation and routing on Cisco routers. There’s so much material here that I’ve broken it up into two posts. Get off the Internet and let’s get started!

(Here’s the previous coverage of Objective 1, Objective 2 and Objective 3. The full list of CCNA objectives is at https://cisco.hosted.jivesoftware.com/community/certifications/ccna/ccna_exam?view=overview.)

For Objective 4, you need to know how routers handle and alter the packets they receive. Specifically, you should understand which addresses in the packet are changed by the router (MAC addresses), and which remain the same in the routing process (source and destination IP addresses).

You should be able to read a routing table and pull information out, such as:

  • The meaning of the codes next to each entry (C, R, S, I, etc). These codes indicate the method by which the route was learned. When you run the command on a router, there is a legend (a key) at the beginning that explains the codes, but that legend may be truncated from the output shown on the exam (those sneaky rascals!)
  • The meaning of all that stuff in brackets next to each route, i.e. [160/5]. Answer: the left side of the slash is the administrative distance (AD) and the right side is the route metric.

For a more in-depth review, study the Cisco command reference for show ip route and related commands.

You should know what a default route is and how to configure one. You also know when it is appropriate to use them (on edge routers or routers with only one connection to the rest of the network, and thus only one route to anything). You should also know that a default route’s main benefit is to reduce the number of routes in the routing table.

You should be familiar with the concept of route redistribution, its purpose, and how it is configured. You should also know how to alter the default behavior of route redistribution by using distribution lists. Make sure that you understand to use an access list to control the redistribution, but apply the list as a distribute list under the configuration of the routing protocol as shown below (taken from show run). In this example, we have instructed the router to only redistribute the network 0.0.0.0 and 10.108.0.0. and deny everything else:

access-list 10 permit 0.0.0.0
access-list 10 permit 10.108.0.0
access-list 10 deny 0.0.0.0 255.255.255.255
router eigrp 1
network 10.108.0.0
distribute-list 10 in

You should understand basic operation of the internals of the router. Specifically, you should know what the following terms and concepts mean, how they all work together, and what is stored in each location:

• Running configuration
• Startup configuration
• NVRAM
• FLASH
• ROM

You should be familiar with possible ports you might find on a router (Serial, BRI, FastEthernet, etc.), and what type of cable is required to connect various devices (straight-through, crossover, rollover/console). (This is also covered in Objective 2.)

Understand how the following mechanisms work:

• Split horizon
• Poison reverse
• Triggered updates
• Count to infinity
• Gateway of last resort

Know how to configure a router from start to finish. This topic is an excellent one to practice in real life. If you don’t have the gear to practice with, get a lab simulator – I personally recommend the Kaplan IT CCNA simulator.

Here are some good examples of basic router configurations:

• Set a Telnet password
• Set an encrypted password
• Configure an IP address on an interface and enable the interface
• Enable a routing protocol on an interface

Very Important: Know your command prompts and the commands for getting in and out of the various prompt levels. Know what commands and functions can be performed at the various prompts. Always check the command AND the prompt in output. Careless errors can cost you.

Practice, practice, practice!!!  You will not have time to figure out how to do these operations on the exam; you only have time to do them. On the exam you will have about 1 to 2 minutes per question. That goes quick if you don’t quite know what you’re doing.

~~Continued in Part 2~~

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