The Transcender Team Weblog

Troy’s checklist for preparing for the CCNA: Objective 3

Welcome back to Week Three of my CCNA study checklist! This week we’ll cover the third objective, which is Implementing an IP addressing scheme and IP Services to meet network requirements in a medium-size Enterprise branch office network (whew, that’s a mouthful; who makes this stuff up?).

(In my previous post here, I took a broad look at the CCNA objectives. In this post, I covered Objective 1. Here’s Objective 2. The full list of CCNA objectives are posted on the Cisco website here: https://cisco.hosted.jivesoftware.com/community/certifications/ccna/ccna_exam?view=overview.)

OK, let’s get started.

First you should understand the difference between public and private IP addresses. This includes knowing:

• What the three ranges of private IP addresses are

• 10.0.0.0 – 10.255.255.255
• 172.16.0.0 – 172.31.255.255
• 192.168.0.0 – 192.168.255.255

• The purpose and benefits of private IP addresses

• Increased security
• More efficient use of public IP addresses

• How Network Address Translation (NAT) allows computers with private addresses access to the Internet and how to configure a router to perform NAT. You should understand the terms inside global, outside global, inside local and outside local.

You should feel comfortable using the following commands to configure a NAT router given a set of requirements, including the type of prompt where they are applied:

• ip nat inside and ip nat outside
• ip nat pool: you should know how this command can be combined with an access list to determine the local hosts that allowed to use the pool of public addresses. This includes knowing how to use wildcard masks to define the range of addresses allowed to use the pool of addresses. (If you need help with that topic, here’s a link: http://www.routerfreak.com/understanding-wild-card-masks/)
• overload parameter: you should know the purpose of this parameter when combined with ip nat inside

Hint and shameless self promotion: The Kaplan IT CCNA Simulator will teach you how do every aspect of these tasks.

You should understand how DHCP works and what the benefits of DHCP and DNS services are. This includes:

• Have knowledge of the packets that are used between the DHCP server (or router) and the DHCP client (DHCP discover, DHCP offer, DHCP request, DHCP ack) and the exact order they occur.
• You should feel comfortable using the following commands to configure a router to perform DHCP given a set of requirements:

• service dhcp (this enables DHCP; the command is usually not required since it is enabled by default)
• ip dhcp excluded address
• ip dhcp pool name

• Also know the network command, the dns server command, and the lease command used for the purpose of defining the mask, the DNS server address, and the lease period for the computers that receive addresses from the DHCP router. These are executed after entering ip dhcp pool mode.

You should be able to examine a network diagram labeled with interfaces and IP addressing information and use it to determine IP addressing problems. This includes problems like:

• Incorrect IP addresses (usually outside of the subnet boundaries)
• Incorrect subnet masks (which result in the above)
• Incorrect gateway addresses

Make sure that you approach this problem in a systematic way. If, for example, Host 1 cannot ping Host 2, trace the entire route from Host 1 to Host 2 and determine at each juncture if the two interfaces required to communicate are in the same subnet.  (Example: trace the address of Host 1 and the address of its gateway, the address of Router 1 and the address of Router 2, the address of Router 2 and the address of Host 2, etc.)

Be able to answer question about VLSM and its application to a network. Specifically, be able to:

• Determine the subnet mask that will yield a certain number of addresses without wasting any addresses. Example: what would be the subnet mask applied to a class C network that would yield at least 50 but not more than 100 addresses? ( hint 255.255.255.192 or /26)
• Determine if two ip addresses are in the same subnet given their addresses and masks. Example: are these two addresses in the same network: 192.168.1.62/26 and 192.168.1.65/26? (Answer: they aren’t.)
• Determine how many IP addresses are possible given the network ID (or subnet ID as some books call it) and the mask. Example: how many addresses are possible in the network 192.168.1.0/27? (Hint: 30)

If all of this is Greek to you,  here’s a link to help: http://www.learntosubnet.com/

Be able to examine a network diagram for IP addressing problems and spot a situation where the mask is configured in such a way that there are not enough addresses for the computers.

Be able to summarize a given set of subnets and know the commands required to instruct a router to use the summarization in its advertisements. (If you have problems with the concept of route summarization, look for an upcoming blog post next week explaining that topic.)

Understand IP addressing backwards and forwards.

• Know the various methods for migrating to IPV6 from IPV4 and the methods of using both at the same time.
• Understand what dual stack and tunneling are and how they operate (protocols, hardware, etc).
• Be able to identify an IPV6 address when you see it and know the types of IPV6 addresses:
  • Link-local (starts with FE8 to FEB)
  • Site-local (start with FEC to FEF)

(The above two categories make up the IPv6 equivalent of private IP addresses.)
• Global (starts with 2000::/3)
• Loopback (yes, the equivalent of 127.0.0.1 in IPv4) which is simply :: 1
• Unspecified (this is the address a computer has until a DHCP server gives it an IPv6 address), which is simply ::

• Understand how IPV6 addresses are formatted and the rules to shorten them by eliminating zeros.
  If all of this sounds like blah blah blah blah blah blah check this out:
  http://www.tcpipguide.com/free/t_IPv6Addressing.htm

Till next week – Happy Studying!

-Troy McMillan