A Great Table of Mnemonics For CCNA Exams

This is a series of articles dedicated to passing the CCNA exam. Part of it is content that I created while I was studying for my own test. If it would be a help to my students I have placed it here on the site.

Knowledge Is Power But Sometimes it's Crazy

I can fill my brain up with some pretty useless information. For some reason its the useless trivia that can stick while the information that may be more urgent or important doesn't make it in. So here are some important facts that you may want to commit to memory for your CCNA exam and hopefully some easy ways to remember that information.

I was trying to come up with a way to remember some of the things like IP Address information, especially IPv6 information as well as some other more esoteric topics like Port Aggregation Protocol, EtherChannel information, and HSRP. I had to really trick myself to get it in my head, but there is something about accessing my tickler for trivia that works.

One thing that I suggest that my students do to prepare for their exam is to plan to write out a block of mnemonic information on the digital whiteboard or slate before the test even starts. At the end of the article I will reproduce that information in a form that can be easily recorded and reproduced on test day.

IP Addressing

IPv6 can be a challenge for many folks. The format can be pretty intimidating. While it is four times as long numerically as a regular IPv4 address it doesn't have to take four times more mental power to work with. There are some special addresses to remember in order to make everything work.

The special forms of the IPv6 address are:

• Link local addresses (fe80)
• Unique local addresses (fc00)
• Multicast Addresses (ff00)
• Unique global addresses (2000)
• Documentation addresses (2001:db8)
• EUI64 Universal/Local (ffee)

Now how do I remember all this? Well one trick is that I have to start somewhere. So I decided to start with what I know. I always remember the link-local address which is (FE80::/10). The reason I remember that one is all the times that I have spent configuring Cisco routers in the past. Whenever you do the link-local address, before you type in the magic command:

ipv6 unicast-routing

You must type in the link local address and fe80::1 is that address that is the default. The next device on the link will default to fe80::2. This corresponds to the Windows APIPA address (169.254.0.0/16).

The second form, the unique local address corresponds to the private addresses that we would normally use behind NATTed networks. The way I remember those is I think about RFC 1918. RFC 1918 is the IETF RFC that discussed unroutable local addresses. So in my mnemonics I start with a list and I remember the FC in RFC and the FC in FC00, like this:

RFC 1918 IPv6 FC00::0//
172.16.0.0/12, 192.168.0.0/16, 10.0.0.0/8
172.31.255.255, 192.168.255.255, 10.255.255.255

By typing it out like this it helps me to remember the inside addresses in case I see one of those in a random question. The more I write the less trivial details I have to remember during the test.

The full IPv6 address mnemonic would look like this:

ff00::/8 - Multicast 224.0.0.1/8
fe80::/10 - Link Local 169.254.0.0/16
2001:db8 - Documentation Address
2000::/3 - Global Unicast Address
fc00::/7 - RFC 1918 Private Addresses
172.16.0.0/12 - 172.31.255.255
192.168.0.0/16 - 192.168.255.255
10.10.0.0/8 - 10.255.255.255

CIDR Host Tables

Another thing that you want to do very quickly before the test starts is to reproduce a subnetting CIDR table.

This table will show the CIDR notation and align it wtih the number of available hosts in a subnet as well as the increased-bit decimal values for the subnet mask.

Here is the example

This table is going to help you when you are asked several questions on the exam about subnet creation. The format of the questions on the exam are such that a person who is not well-versed on the subnetting question is going to spend a lot of time on making the subnets. The way that the test asks it is that one question will be written to ask about a subnet which must be formed from an existing subnet. In order to solve the problem the test taker must usually create three or four more subnets from a larger one and pick from one of those to select an answer. Writing down this handy chart will save time in this process and it will prevent you from trying to do these types of problems in your head, which can cause errors.

The first row labeled CIDR gives the slash notation for the number of masked bits in the network portion of the IP address starting at the third-octet boundary position, or /24. The second row labeled Mask is the cumulative decimal value of the netmask bits from left to right starting with the first zero bit of the fourth octet and continuing on to having all the bits set. This will allow you to visually have the subnet mask created from the CIDR-notation in a very quick period of time without having to mentally compute it. The last column, IP's, are the number of IP addresses in this mask set. Note that it is not the number of hosts.

While the questions will always ask you in most cases the number of hosts, I specifically leave this out in my chart. I need to know the number of IP addresses in a subnet block. I do not care about the number of hosts unless the question specifically asks about hosts. Note that the gateway address is always a host address. The two addresses that make up the difference between IP's in a CIDR block and hosts in an IP block are well-known: the network number or subnet identifier and the broadcast address. These are always positional. They are always first and last in the IP block.

Route Administrative Distances

The last thing you want to have here are the administrative distances for the varying route types. Cisco routers handle these different route types and give specific priority to competing routes based on the type of route. This means that a certain routing protocol advertising the exact same route as another would get priority given to it.

These again are just things to memorize and are shown in the following table:

    C/Local  0
    Static   1
    eBGP    20
    EIGRP   90
    OSPF   110
    RIP    120
    iBGP   200

Key things to remember is that a static route takes precedence over an external BGP route which takes precedence over all other routes. The other is that Internal BGP one of the lowest priorities. It is imperative that a test taker memorize this chart and values.

Stress relief

One of the most important things that memorization of these key topics will do for you as a test taker is to reduce test anxiety. If you memorize these things and spend the first three minutes of the test writing them down using the provided electronic white board (or physical slate), it will serve to reduce your test anxiety.

That's why memorization of these is so important. One thing that this will do is get your analytical juices flowing during the first part of the test. Don't worry about what the first question is, just immediately write the memorization topics down. Then you can start the test.

Good luck on your CCNA adventure.