The Networking Basics You Need to Know in Order to Pass the CCENT Exam – Part 2

Sorry for the delay between posts.  I've been a little under the weather since returning from vacation.  I have also very busy at work.

Part 2 of this series begins with one of the harder skills to master in networking; IP Addressing Resolution and Subnetting.  Ask anyone who has ever studied to take the CCENT or CCNA exams, and they will most likely agree with me.  However, I think that most teachers will over-complicate it by stressing binary conversions, the base2 numbering system that breaks this all down to a series of ones and zeros.  I find that it’s easier and faster to work with IP addressing if you use as little binary as possible.  Why? Because it’s too slow to work with and it’s an extra step that’s just not necessary.  I’ve stressed in my earlier posts that speed is essential when taking the CCENT/CCNA exams. Since IP addressing resolution is prevalent throughout the exams, it only makes sense to learn a few shortcuts.

Please be patient and read the post a couple of times.  When you get it (and you will) you're going to wonder why you thought it was so hard in the past.

Without wasting any more time, here is an explanation of the next basic skill in the series:

Resolving an IP Address – Find the Network, Broadcast, First and Last Host, and Next Network Addresses

A typical question might ask you to find the network address where a given host address resides, or find the useable host address range for a given network. The useable address range does not include the network address (first) or broadcast address (last) for that network. If you are designing an addressing scheme, you will need to know how many networks you can create, and where one networks ends, and another begins.

Let’s look at a typical host address and mask, and then find the network address:

192.168.1.55 /24  or  255.255.255.0  (if you are given the mask in dotted-decimal)

The first thing that you need to know is that the subnet mask is used to filter out the host information and preserve only the network information of the address. The mask is used to show you where the network bits end and the host bits begin, so you can zero out the host bits. When a router looks at the destination address of a packet, it initially only cares about the network address in order to make a decision on where to forward the packet next.

In the example above, /24 means that the first 24 bits of the address (from left to right) are network bits, which should be left as is, and the last eight bits should be changed to zeros (0). Recall that there are 32 bits in an IP v4 address. The dotted-decimal mask, 255.255.255.0  means that all of the bits in the first three octets are set high (or are 1’s), and all of the bits in the last octet are set low (or are 0’s). When evaluating each bit in the host address you would compare it to each matching bit in the subnet mask. Just remember the rhyme: If it’s high, let it ride. If it’s low, let it go. I just made that up (And my English teacher said I would never amount to anything). Here is how that process would look like in binary.

Notice that only the ones (1’s) are left from the first 24 bits.  All of the host bits are changed to zero’s (0’s).  In fact, the first three octets from the host address are exactly the same after applying the mask. Two important shortcuts to learn from all of this are:

1. If the mask bits are all 1’s in a given octet, then the matching host octet stay’s the same (like in octets 1-3 in the example above)
2. If the mask bits are all 0’s in a given octet, than the matching host octet changes to all zero’s (like in octet 4)

Important Point: When resolving a host address to a network address, you should always be able to resolve three out the four octets very quickly by using the above shortcuts.

Here are five host addresses followed by the 3 octets that are easily resolved in red:

166.32.114.184   255.255.224.0   ======>  166.32.114.0

168.168.10.65   255.255.255.224   ======>  168.168.10.65

149.90.165.115  /21   ======>  149.90.165.0

126.5.43.153  /15   ======>  126.5.0.0 

150.163.46.151   255.255.128.0   ======>  150.163.46.0

Note: The octet that's left in bold black text would still need to be resolved (coming).

Let’s look at a couple examples where we find the network address from a given host address.

Finding the Network Address - Example 1

Find the network address from the following host address and mask:

172.16.76.125 /18  or  255.255.192.0

Octets 1, 2, and 4 can be resolved with just a glance:  172.16.76.0. Octet 3 still needs resolving.

Here’s the binary depiction. As you can see, writing it out in binary takes a lot more time than using the shortcuts.

To resolve the third octet without binary we use the Jump Number method.  The Jump Number is the decimal value of the last network bit in the subnet mask (see below).  The 18^th bit (as in /18) is equal to 64, which means that the network number for that octet will be some increment of 64, starting from zero (0, 64, 128, 192). 

 

 

 

Tip: The host number will always be greater than or equal to the network number for the octet that you are resolving with this method

Since the number in the host address for that octet was 76 and it falls between 64 and 128, the network number is 64 and the network address is 172.16.64.0.  The network number for the unresolved octet will always be an increment of the Jump Number as long as you remember to start counting at 0.

Finding the Network Address - Example 2

Find the network address from the following host address and mask:

188.42.59.45 /21  or  255.255.248.0

Since the network bits end in the third octet again (you can see this better by looking at the dotted-decimal mask) the unresolved octet will be octet 3 again. The three octets that can be resolved at a glance are 1, 2 and 4 or 188.42.59.0

This time the last network bit in the subnet mask is the 21^st bit, which is equal to 8.

 

By the way, any time you're given the subnet mask in dotted decimal, you can find the Jump Number just by subtracting the octet value that contains last network bit from 256 (256-248 = 8). In the last example we would subtract 192 from 256 (256-192 = 64).

Back to our example: The jump number that was found is 8. This means that the network number for that octet will be some increment of 8, starting from zero (0, 8, 16, 24, 32, 40, 48, 56, 64, etc.. .). Hint: you can stop counting once you pass the host number for that octet (59).

Since the number in the host address for that octet was 59, which falls between 56 and 64, the network number is 56 and the network address is 172.16.56.0.

I will stop here and we will finish this topic next time. In the meantime, here are several host addresses for you to resolve to network addresses:

200.55.116.97  255.255.255.240

88.65.146.77 /13

145.85.117.252  255.255.224.0

196.145.98.177 /27

166.98.225.77  255.255.252.0

I will post the answers tomorrow. Your comments and questions are welcome.

And the answers are:

200.55.116.97  255.255.255.240   ======>  200.55.116.96  

(First three octets don’t change; Jump# is 16 – 256-240)

88.65.146.77 /13   ====> 88.64.0.0 

(1st octet doesn’t change; Octets 3-4 change to 0; Jump# is 8 – 13^th bit = 8)

145.85.117.252  255.255.224.0  ===> 145.85.96.0  

(1st two octets don't change; Octet 4 changes to 0; Jump# is 32 – 256-224)

196.145.98.177 /27   ===>  196.145.98.160

(First three octets don’t change; Jump# is 32 – 27th bit = 32)

166.98.225.77  255.255.252.0   ==>  166.98.224.0 

(1st two octets don't change; Octet 4 changes to 0; Jump# is 4 – 256-252)

Your questions and comments are welcome.

-Jim (rev 7/26/2014) 

 

My apologies for not posting for awhile but I've been away and since returning I've been swamped. Here is a News Release that ECC sent out this afternoon.  Please do me a favor and send a link to anyone that you think might benefit by this new certificate released by ECC.

 

Thanks!

Jim



 

 

July 10, 2014

FOR IMMEDIATE RELEASE                                 

ECC introduces Network Support Technology Certificate Program, with information session on July 23

In support of their new Network Support Technology Certificate Program beginning this fall, Erie Community College will be holding an information session on program specifics at its South Campus (4041 Southwestern Blvd., Orchard Park), Building 5 (Room 5112) on Wednesday, July 23, 2014 from 6:00 p.m. to 7:30 p.m.

The session will include a short presentation, department tour and a question and answer period concerning the new program, which will be offered through ECC’s Networking and Telecommunications Technology Department and in conjunction with the college’s Cisco Networking Academy. According to James Stranz, program coordinator of the academy, the program’s arriving at the right time for both the region and prospective students. 

“A program like this has been necessary for a long time” said Stranz. “Today, there are networks in most every business and home. Employment in this field is no longer relegated to large telecom companies like Verizon and Time Warner. Instead, jobs are found in almost every public and private company.”

According to the U.S. Bureau of Labor Statistics, employment in this field is expected to grow by 28 percent between 2014 and 2020. Job opportunities exist for PC support technicians, equipment installers, technical support specialists, structured cable installers, network administrators, network engineers, and technical sales consultants.

ECC’s new 24-credit program can be completed in as little as eight months, with students only having to attend class two evenings per week, with options also offered on Saturdays. Classes will be held at ECC’s South Campus, North Campus, and Ingram Micro’s campus in Williamsville. Students can also complete the required coursework during the day by taking courses through ECC’s Networking and Telecommunications Technology Program, which offers an Associate in Applied Science degree.

Students in the Network Support Technology Certificate Program will be introduced to the field of networking and PC hardware and software support; participate in classroom laboratory exercises in all of the core courses; and be prepared to take the Cisco entry-level networking support certification exams, like CCENT and CCNA, as well as the CompTIA A+ computer support certification exams. According to Stranz, “a one-year certificate that’s enhanced with industry-standard certifications makes an individual very employable in a short period of time.”

The program’s webpage can be found at www.ecc.edu/academics/programs/networksupport. For more information, please attend the July 23 information session, or contact James Stranz at (716) 851-1737 or stranz@ecc.edu.

Since 1946, Erie Community College has met the needs of a diverse student body while contributing to the economic vitality of Western New York. As a member of the state’s SUNY system, the three-campus college provides flexible, affordable and accessible educational programs in an accommodating academic environment. Equipped with the knowledge of these programs, ECC’s faculty, staff and students strive to enrich their host communities through skill, service and partnership.

My CCENT Certificate Has Arrived

I received an email yesterday with a link to my certificate (suitable for framing). Not bad, only a couple weeks after passing the exam. I thought that everyone would like to see what it looks like and hopefully you will be inspired to take the exam and get one of your own. I covered the all-important numbers to protect the innocent (me), although I'm not sure they could be used for anything nefarious.

By the way, I just want to point out that I've passed this exam many times over the years, as well as higher ranking exams.  None of what I'm doing here is for self promotion, it's for helping my students, both past and present, to get certified.  However, I am always looking for new students.  I feel we have a great program here at Erie Community College and I want everyone to know about it. 

That being said, here are a few links to the program websites that utilize the Cisco Networking Academy courses at ECC:

Network Support Technology Certificate Program (New 1-Year Program)

http://www.ecc.edu/academics/programs/networksupport

Networking and Telecommunications Technology (2-year Program)

http://www.ecc.edu/academics/programs/telecom/default.aspx

Information Technology with Networking Concentration (2-year Program)

http://www.ecc.edu/academics/programs/infotech/default.aspx

The Cisco Networking Academy Partenership Program (A Service Program)

http://www.ecc.edu/academics/partnerships/cisco

For More Information:

Email: stranz@ecc.edu
Phone: 716-851-1737

-Jim (revised 6/28/2014)

The Networking Basics You Need to Know in Order to Pass the CCENT Exam – Part 1

I'm falling a little behind in my posts. I am still working on Part 3 of the "How to use your cheet-sheat series", but I will get back to it soon, I promise. I will be away at a conference next week, but I will try to publish the article before I leave. Today I have the first installment of a two-part series on the fundamentals of networking that are necessary to know in order to pass the CCENT exam. By no means is it conclusive, but it's a foundation that you need to build upon.

My favorite part about being a teacher is helping students find jobs once they complete their degree.  When I can help a student find a job it makes me feel like I’ve made a difference in their lives.  One way I can help them, besides the normal classroom education that I’m paid to deliver, is to help them to get professionally certified so they gain that extra edge in the job market.

Since I teach computer networking, the Cisco Certified Entry Networking Technician (CCENT) certification is the entry-level cert that I encourage students to obtain.  That being said, here are some of the basic skills and the general knowledge that a student needs to pass the CCENT exam:

1. Basic Device Configuration of Switches, Routers and hosts

A student should be able configure these devices so that they provide end-to-end connectivity in a small network. This includes being able to configure:

• Device hostnames in order to differentiate one device from another
• IP addressing on LAN and WAN interfaces (including descriptions)
• Basic security (passwords and encryption) on all interfaces and the console port
• A routing protocol and static routes
• VLANs and trunking

More than likely you will need to display these skills within a simulation question, as well as 8-10 regular questions.

2. Testing End-to-End Connectivity and Verifying a Hosts IP Address

Anyone who’s pursuing there CCENT certification should be able to use connectivity commands like ping and traceroute as well as ipconfig, which is used to check the IP address of the host, and so much more.

3. Effectively Use the Top 4-8 Show Commands for Verification and Troubleshooting

I find that troubleshooting is the hardest thing to teach. Of course, practice is the key to mastering the art of troubleshooting, and knowing which Cisco IOS show commands to use is a good start. Here are the ones I feel you must know:

show running-configuration – The output of this command yields a lot of information to verify and troubleshoot your basic configuration and more.  It will provide you with the most bang for your buck when it comes to investigating how a router and switch are configured.

show ip interface brief - The output of this command will display the state of your interfaces along with the interface address. Simply put, if your interfaces are down, end-to-end connectivity is not happening. Note: there are several other “show interface” commands that will provide more information, however this is the easiest one to interpret, and most times you will find the information that you need. 

show ip route –If the two previous commands fail to provide you with enough information to solve the problem, this command could do the trick, however, it is the hardest of the three to interpret. Basically the output will show you the networks you’re able to reach and how to reach them. However, there’s a lot more to it. By the way, the first two commands can be run both on routers and switches. You would run this command only on the router.

show mac-address-table – This command is similar to the previous command, accept it’s for switches. The output displays the mac address of each device connected to the switch, and the port where each device is connected. 

show vlan  – VLANs play a huge role in today’s networks. This command will allow you to keep track of the VLANs that are configured on a switch, but which ports belong to which VLAN. This comes in handy if connectivity on a switch is not working like you think it should.

These last two commands are for the switch only.

In Part 2, I will look at the following three basic skills:

1. Resolve an IP Address – Find the Network, Broadcast, First and Last Host, and Next Network Addresses
2. Understand Switching and Routing Decisions
3. Know the Characteristics of the Transport, Network, and Data-Link Layers of the OSI Model

Your comments are always welcome.

-Jim Stranz (revised 6/27/2014)

Why you’re better off taking the CCENT exam rather than waiting and taking the CCNA composite exam

I'm going to take a little break away from the How to Use Your Instant Cheat-Sheet Series in order to take a look at the differences between the CCENT and CCNA exams, and why I beleive that you should almost always start by taking the CCENT exam.

For years now I’ve been advising my students to take the CCENT (ICND1) exam first, before taking the ICND2 on their way to getting CCNA certified. Meanwhile most of my colleagues would tell the students to just take the CCNA composite exam (CCNAX) and bypass the CCENT exam altogether. Their reasoning behind their theory is that you only will need to drive to the testing center twice, plus you will only need to study for the exam once. I totally disagree with that reasoning!

Here are several good reasons for starting out by taking the CCENT exam first:

1.       The CCENT exam is flat out easier than the composite exam. If you’re taking you’re first certification exam you will definitely appreciate this, since the entire exam experience is stressful enough, and you don’t need the added stress of more difficult content.  Follow my advice and you will feel a lot more comfortable with the testing experience thereafter. Plus you don’t have to study all of the content at once, you can cut it in half.

2.       If you pass the CCENT exam you’ve completed the pre-requisite for the CCNA specialization exams like CCNA Security, CCNA Voice, CCNA Wireless or CCNA Data Center. You’re no longer required to become CCNA certified first, before taking these exams.

3.       If you’re a Cisco Networking Academy student you can see the fruits of your labor after just two courses, and one semester, if you’re taking the classes at ECC.  You can become employable in as little as four short months!

Finally, remember that one reason for taking the composite exam is that you’ll only need to study once?  That may be true, but it will take you twice as long to learn everything that’s going to be on the exam.  If you’re a Cisco Networking Academy student you will need to take four courses, and add at least another four or five months on to your quest for employment. Also, wouldn't be great to have that (CCENT) certification in your hands after passing just one (easier) exam.

Your comments are welcome.

-Jim (revised 6/24/2014)

How to use your instant cheat-sheet – Part 2

In today’s installment we will look at a typical question you might find on a CCENT or CCNA exam, and we will use Table 1 from my previous post (See: How to use your instant cheat-sheet – Part 1) to help answer the question.
In the following figure we see a typical troubleshooting question that I like to refer to as a “what’s wrong with this picture” question.  In this scenario, Host C cannot communicate with hosts A and B. What is most likely the problem?

 

 

 

 

 

 

 

The first thing I would do is check to see if host C is properly configured and able to communicate with its default gateway.  If host C can’t talk to its default gateway, I can’t talk to hosts on another network.  Think of the default gateway like the only door in a room.  If you can’t open the door, you’re not getting out of the room.

Let’s use Table 1 below to see if Host C and the default gateway are on the same network.
 

 

 

 

 

 

Host C has a mask of /27.  Looking at our table we see that /27 lines up with the Jump Number 32.  That means that the fourth octet of Host C’s network address is an increment of 32, i.e. 0, 32, 64, 96, etc.. . Therefore, Host C resides on the 172.16.31.64 network, which has a valid host range of 172.16.31.65 through 172.16.31.94 (if you’re not sure how I arrived at that, ask). Note: 172.16.31.95 is the broadcast address and 172.16.31.96 is the network address of the next network. 

Now let’s look at the default gateway address, 172.16.31.93 /28.  Looking at our table we see that /28 (see below)lines up with the Jump Number 16.  That means that the fourth octet of the gateway network address is an increment of 16, i.e. 0, 16, 32, 48, 64, 80, 96 etc.. . Therefore, the default gateway resides on the 172.16.31.80 network, which has a valid host range of 172.16.31.81 through 172.16.31.94.

 

 

 

 

 

The key here is that Host C and the default gateway are on different networks; therefore they are unable to communicate with one another.  Any time Host C wants to communicate with a host on another network it needs the cooperation of the default gateway (think of the gateway as a type of doorman).  Of course realizing that the masks were different from the start would have been enough to answer this question; however my intent was to show you how to use the table.

By the way, they will generally show one mask in prefix notation and the other in dotted-decimal notation as depicted below.

 

In this case we could use the table to convert prefix notation to dotted-decimal notation, or vice versa, and then compare the two. For example:

/27 maps to a dotted-decimal mask of 255.255.255.224, and /28 maps to a dotted-decimal mask of 255.255.255.240.

In Part 3, I will introduce the other two tables that should be included on your cheat-sheet and I will work through another problem.

-Jim (revised 6/21/14)

How to use your instant cheat-sheet – Part 1

A few weeks back I shared my ideas for an instant cheat-sheet with all of you.  I then told you how I was able to successfully recreate it and use it on the CCENT exam (See the post “Observations from taking the CCENT exam - Part II”).  I can’t stress this enough; this practice is all perfectly legal and is very effective at raising your score on the exam.  However, you need to know what the information on the cheat-sheet stands for, you need to know how to apply the information from your cheat-sheet on the exam, and you need to know how to recreate the cheat sheet in the short period of time that you have before the exam begins.
In today’s post I want to explain Table 1 on the cheat-sheet. I will explain the other tables and show you how to use the tables in future posts.

Table 1: Conversions and Jump Numbers

 

 

 

 

You should be well aware of the top row, the decimal value of each bit in an octet.  The bit on the right is bit 0 and is worth “1” which is derived from base2 numbering, 2⁰  or 2 raised to the zero (0) power. As you can see, the value of the bits double as you move left and the power of 2 increases (2¹, 2², 2³, etc).  That’s the beauty of base2. The values also represent the Jump Number, or number of addresses that make up each network derived from the original classful network (more on this later).

Now that we’ve established the meaning of the top row, we can now examine rows 2-4. Rows 2-4 represent the bits in octets 2-4 and the possible subnet masks in prefix (slash) notation. This is extremely easy to recreate since all you’re doing is counting, starting at the 9^th bit position. Note: you should never see a subnet mask that is less than 8, unless it’s a special address or illegal.

What does all of this mean? Recall that every IP address has two parts; the network portion and the host portion. A mask of /20 means that the first 20 bits (from left to right) are network bits, and the 12 bits that remain are host bits.  In most IP addressing questions we are interested in resolving an address to the network portion of the address.  All of the host bits then become zeros (0). For instance, the address 172.16.123.88 /16 becomes 172.16.0.0 when you apply the subnet mask. The /16 implies that there are 16 network bits (from left to right) and the remaining 16 bits are host bits and they are filtered (zeroed) out.

The bottom row represents the other type of mask that you will see (dotted-decimal).  The number is calculated based on the sum of the network bits (from left to right) in a given octet. A mask of /20 means the first 16 bits in octets 1 and 2 are all part of the network, along with the first four bits of octet 3.  If you add the decimal values of the first four bits of octet 3, the sum is 240 (128+64+32+16). Therefore the mask /20 converts to 255.255.240.0. Remember, the remaining bits, bits 21-32 are all host bits and are changed to zeros (0) when determining the network address.

In Part 2 we will see how we can apply this to a problem.

-Jim (revised 6/19/14)