Well, I just finished reading chapter 9 of the BCMSN study guide. If you look at my schedule plan, that covers all of the reading materials I set out to accomplish for this week (up to Sunday). I’m kind of cheating though. Although it appears that I’m reading a lot, I’m actually skipping the ‘configuration exercises’ at the end of each chapter. There’s about 5-8 pages of that for every chapter. I thought that’s fine for now. Anyway, my main goal for the first phase is to get a complete overview of the whole BCMSN track by reading through the whole book. Then dive in deeper to the core subjects. Additionaly I wanted to get through the first phase before my wife gives birth in a couple of weeks.

Tonight I will be starting with the QoS chapter and hopefully be able to progress at the same pace I was going for the last 2 weeks. I say hopefully because I’m a little doubtful. QoS is an entirely new subject for as I’ve never touched it before. Whereas, the previous weeks were pretty much a series of CCNA switching review with a some added new materials. We’ll see how it works out at the end of the week.

While trying to organize the multitudes of Cisco documentation web links I’ve accumulated over the past year, I re-discovered these links that I dismissed as trifle information back when I first came across them. I guess I felt that way then because I didn’t consider the information lengthy enough to contain comprehensive theoretical background:

• BGP: Frequently Asked Questions
• EIGRP Frequently Asked Questions
• IP Routing Frequently Asked Questions
• ODR: Frequently Asked Questions
• OSPF: Frequently Asked Questions
• Cisco IOS Multicast Q&A

But while looking over some of the FAQs contained in them, I was surprised to discover how many of the very same questions appeared on the BSCI exam (albeit worded and used on the exam a little differently – but the same information nonetheless).

In my opinion, in order to get the most out of the FAQs, you’ll have to thoroughly understand the theories behind each technologies first – this is done by reading your theory books. Once you understand the general makeup and operation of the protocols, the FAQs can serve as review questions that  can be used to verify how much of the details you can remember. The way I would use them in the future is to categorize each protocols, copy the questions into a set of index cards/flash cards (or something similar) and drill myself until I’ve memorized the information.

Newly minted digits: CCIE#23895

Head over to Netengineer.org (aka. CCIE Paradise) and congratulate Andy Lee for passing the CCIE lab on Friday.

Mon, 23-Mar-09: Chapter 5: Read pp. 217 – 250 – Spanning-tree protocol, PVST+, RSTP.
Tue, 24-Mar-09: Chapter 5: Read pp. 251 – 273  – Multiple spanning tree, End of chapter exercises.
Wed, 25-Mar-09: Chapter 6: Read pp. 275 – 315 – 802.1D Enhancements: PortFast, BackboneFast, etc; BPDU Guard, etc.
Thu, 26-Mar-09: Chapter 7: Read pp. 317 – 353 – Etherchannel, CDP, L3 protocol filtering, Broadcast & Multicast supression. etc.
Frid, 27-Mar-09: Chapter 7: Read pp. 354 – 383 – IEEE 802.3 flow control, UDLD & aggressive mode UDLD, end of chapter.
Sat, 28-Mar-09: Chapter 8: Read pp. 385 – 409 – Inter-VLAN routing, IP broadcast forwarding.
Sun,29-Mar-09: Chapter 9: Read pp. 411 – 439 – CEF-based multilayer switching.

This past weekend, I concentrated mostly with an overview of Spanning Tree and its operation.  I also watched a little bit of IPExpert’s free vLecture on spanning tree. I’m a little bit ahead of my reading schedule as I’ve already finished the scheduled reading on Chapter 5. It was a little challenging getting through that chapter for some reason. I felt like CCNA all over again when I struggled with Spanning Tree. I don’t find it a difficult subject. It’s just that somehow the concept doesn’t stick as well. Good news is, I understand it much better than I did when I first learned it in CCNA. And I didn’t find too much new materials. In fact I’ll probably re-read the CCNA material during the second phase of my studies as I found Wendell Odom’s style of writing much easier to digest – and I somehow feel that the CCNA material was more “in depth” in its coverage. Or maybe it’s just my perception because it was completely new to me last year and much more overwhelming in details.  I’ve started Chapter 6 today and I’m shooting to finish that tonight – hopefully even start chapter 7 tonight. Chapter 6 is very short. There is only a little over 25 pages. I can probably knock 20 pages of it during downtimes at work. I’m hoping to get as much reading this week as I can because I might not have much time to read next weekend as we are celebrating my son’s 3-yr birthday party.

It’s been 3 days in the making, but I’ve got the first phase of my study schedule completed. See the list by clicking on the BCMSN STUDY SCHEDULE tab on top of the page.

This week’s scheduled reading is posted below. I’ve already read ahead so I’ve completed the scheduled readings up to Friday. I’m starting the Saturday schedule tonight and hopefully be able to stay ahead of the game in case my wife gives birth a little earlier than expected.

Mon, 16-Mar-09: Chapter 1: Read pp. 3 – 30 – Enterprise Network Architectures: Enterprise Composite Model, SONA, IIN, etc
Tue, 17-Mar-09: Chapter 1: Read pp. 31 – 60 – Continuation of Enterprise Model, Intro to Catalyst switches
Wed, 18-Mar-09: Chapter 2: Read pp. 61 – 92 – Data-link layer technologies, Multilayer switched network design.
Thur, 19-Mar-09: Chapter 3: Read pp. 95 – 125 – Initial Catalyst switch configurations, IOS File System (IFS), Software images.
Fri, 20-Mar-09: Chapter 3: Read pp. 125 – 147 – Basic switch troubleshooting practices.
Sat, 21-Mar-09: Chapter 4: Read pp. 149 – 185 – VLANs: configuring , verifying , Private VLANs, VLAN trunking.
Sun, 22-Mar-09: Chapter 4: Read pp. 185 – 215 – VLAN Trunking Protocol (VTP), End of chapter exercises.

I didn’t wait too long to get started on my next quest towards completing the CCNP. After I passed the BSCI exam on Saturday, I rested on Sunday and got back on it again on Monday. I actually received my BCMSN books last Friday and been itchin to crack open the books.

Well now I’m almost back into full swing. I’ve already read about two and half chapters of the Cisco Press Study Guide since Monday. I’m hoping I can get through all 800 or so pages of the book in under a month before I begin to re-read and do a “deep-dive” into each chapters.  I’m back on the drawing boards again in terms of my study strategy. My strategy from the last exam (although effective) just took way too long than I wanted. I’m hoping I can find a better strategy this time.

Of course, I will make another attempt to publish my study schedule on a separate page (see tabs above). I will try to be more concise and cleaner in my approach. The BSCI study schedule was a bit of a mess - I’m actually planning on updating it with some notes of my previous progress just for the benefit of those trying to compare their progress to mine.

And true to my style, I will continue the bulleted notes of my studies that you’ve been accustomed to seeing over the last year. I’m just not sure when I’m going to start publishing my notes. I want to complete the study guide cover to cover first and then maybe start my notes when I do the chapter by chapter deep dives. I haven’t quite decided on that yet.

As far as the materials I’ll be using, so far I have:

1. Building Cisco Multilayer Switched Networks (BCMSN) (Authorized Self-Study Guide) (4th Edition) by Richard Froom, Balaji Sivasubramanian, and Erum Frahim – This is going to be the primary text I’ll be using. It has some decent lab exercises at the end of each chapters similar to the ones from BSCI study guide.
2. CCNP BCMSN Official Exam Certification Guide (4th Edition) by Dave Hucaby – I bought this primarily for the practice test engine companion CD that comes with it. It has considerably fewer pages than the study guide but hopefully, it will help reinforce the topics I need to learn for exam purposes.
3. Cisco.com Documentation – This was an invaluable resource for me while studying for BSCI. I’ve printed pages upon pages of configuration guides, tech notes, white papers for individual technologies I covered. I have them all categorized and neatly compiled in 3-inch binders.
4. Dynamips/Dynagen - I’m not sure how much of it I will use but I’m going to try to get the interface from the emulated software to interface with the real switches.
5. Catalyst Switches:
   • 2 x 3550 Catalyst switches – I ordered them from Ebay and I shoud receive them any day now.
   • 3 x 2950 Catalyst switches – These are ones I’ve collected over the past year while studying for CCNA and BSCI.
   • 1 x 2924 Catalyst switch – I just bid on it on Ebay and happened to win. It was a decent price for adding a bit more complexity for lab topologies

Other things I’m considering getting, but haven’t decided on yet:

• CCNP Building Multilayer Switched Networks (BCMSN 642-812) Lab Portfolio  - I got the one for BSCI but I hardly used it.
• CBT Nuggets or Train Signal - It’ll depend how I feel about my progress during my readings. Price is also an issue.

The plan is to study 2-3 hours on the weekdays and 4-5 hours on the weekends. I’m pretty good with the weekday schedule, but the weekend schedule is pretty tough for me so I’ll see what comes of that. I’ve been tracking my study hours (using a stop watch) as well for the last few months and I find it helpful for assessing how I’m progressing. 

My goal is to attempt and pass the exam by the end of July – if not sometime in August. That gives me about 4 to 5 months. That is a tall order for me as we are expecting our second child in less than a month from now. There is no telling what my schedule is going to be like in terms of studying.

I’m not the only one who passed an exam this weekend:

• A more significant achievement was accomplished by Brandon Carroll and gaining his digits by passing a difficult CCIE Security lab on Friday. Head over to his blog to congratulate him.
• Also, another fellow blogger passed his BSCI exam yesterday. Head over to Dani’s (aka Newton’s CCIE Pursuit blog) and leave your congratulatory comment for a huge step forward toward attaining his CCIE goals.

I STUDIED!!!

That’s right. I started studying for the BSCI just right after I passed my CCNA exam last year – that’s approximately 9 months ago. Not counting the 1.5 months that I was not studying for BSCI  due to a project at work, I studied for this test for a total of about 6 months – give or take a few.

Here’s how I did:

Implementing EIGRP operations: 88%
Implement multiarea OSPF operations: 70%
Describe integrated IS-IS: 85%
Implement Cisco IOS routing features: 80%
Implement BGP for enterprise ISP connectivity: 81%
Implement IPv6: 75%

Score needed to pass: 790
My score: 855

Obviously, it is not a perfect score. But I am extremely happy with the results given that my initial feeling just after I finished the exam was that I probably scored in the low 800s - I was hoping that at least. There was a big part of me that thought I was screwed and that I probably should think about rescheduling again. I honestly didn’t know (based on my performance during the test) whether I passed or not.

I took the test in Irvine, CA – about one hour away from where I live. There are other testing centers within 15 minutes of me but I chose this testing center because it is the only one close enough that offered exam dates on weekends. I arrived at the testing center about 10 minutes late and had to wait another 30 minutes because the room was packed. I’ve never seen that place as busy before from the last three times I’ve been there. There were usually only 4-5 people there in my previous trips. <Just got interrupted by my 3yr old: “Are you writing about routers again?’ LOL! Precious!> Normally I’m cool with distractions since I can be pretty good with blocking things out. But for some reason, it was hard for me to concentrate this time. I attributed that to nerves. For the last two weeks I hit the books really hard and was unrelenting in my studies – reviewing from 7pm – 1am. I told my wife that I felt good about this test - that I’m very confident I was going to pass. However, I started feeling the jitters and nervousness around Thursday and Friday before the test. My wife thought it was because of stress. I thought its a combination of that, lack of sleep, and an unusual high dose of caffeine over a prolonged period - something I don’t ingest on a regular basis.

I found the test extremely challenging. For someone who does not work with Cisco devices on a regular basis or does not have at least 2 or 3 years of experience with it, you will find that the exam really exposes not only your ability to memorize little bits of minutiae, but also how you use that knowledge to apply it to different kinds of scenarios that you might not necessarily see on a regular basis. That’s probably an obvious statement. But that was just the very thought that kept playing in my head over and over. Even then I started wondering how someone who works with these technologies every day would feel about the test. There were some questions that I thought might have applied to real world scenarios, and there are some that I thought were just purely theoretical and that would never be done in the real world. But then again what do I know? I just hit Ctrl-Alt-Del all day for my users.

Here are some more of my thoughts about this exam (especially for those looking to take it soon):

• There is a pretty hefty dose of multicast on this exam. If you are using the study guide by Teare and Paquet, you might find that the materials provided in the books might not be enough. I know for sure I saw some things in there that I’ve never seen on the book. Either I never saw it, or just ignored it.    Pay close attention to the details in that section. Learn to interpret the show commands. I can’t say which show commands so it’s probably in your best interest to know them all.
• Come in prepared for IPv6. I thought I did. And for the most part I think it wasn’t too bad. But there was a section where I spent a considerable amount of time tyring to figure out. I think I did. Again, I saw things on IPv6 that I thought they would not test. The way the study guide covered IPv6, I got the impression that there are things that were not going to be tested on the exam – based on the amount of coverage (or lack thereof) given to them in the book. And again I was caught surprised by it. I think I did ok on the question though.
• Coming into the test, I was most confident with IS-IS and BGP. And although I spent twice as much studying OSPF than all the others, it’s strange that I received the fewest points on it. Reading Cisco forums over the last month gave me an indication that IS-IS was one of the big three that stumped most people (multicast and IPv6 being the other 2). However, I didn’t see it that way about IS-IS. I thought it was straightforward and easy. If you read the section of the BSCI study guide thoroughly, you should do fine with IS-IS. With BGP, I supplemented it with Doyle’s Routing TCP/IP, Volume II (CCIE Professional Development).
• One surprising area I didn’t expect to do as well on (but ironically did do well) is EIGRP. That and routing update manipulation (distribute-lists, route maps) were the ones I dreaded and hoped not to see too much of on the exam. Well, I pretty much knew that I’d see a good amount of EIGRP. But I was hoping not a lot of route maps, access-lists, etc. But there is a fair amount of it, so know it. 
• It’s been said before in the forums and anyboby else who has taken the exam before: ”Time Management“. I think I managed my time just perfectly. By the time I clicked the answer on the last question, there was exactly 30 seconds left on the exam. I did spend a good 15 minutes on a couple of different sims though. But picking up from the last two tests I’ve taken, I learned not to double-read the questions and learn to scan it a little faster. Because I made myself do this, I also forced my brain to concentrate better knowing that I will only get one chance to read the question. Of course I didn’t do this technique for every question. Obviously there are some that will be worded a little bit funny and you’ll have to re-read it again. But try not to do this for every question because you’ll definitely run out of time. What I did was scan the multiple choices, read the question, then read the choices again. I made sure I only gave myself 1 minute at most to answer the questions. If you’re prepared, there will be some that’ll only take you 10 seconds before you can come up with the answer in your head before even seeing the choices. I love those types of questions.
• Be mindful of what you are clicking. I missed a lot of points on a scenario-based question when I clicked “next” question instead of clicking the button for the next section of the same question. I know I got the first one right, but I’ll never know how I would have done on the next few scenarios. So be careful. Manage your time but don’t be too careless.
• This is more of a gripe than anything: I got one sim question where no matter how many times I typed in a command, the wrong value comes up when you do a “sh run”. I know I was typing it correctly and I double, triple, quadruple, and multiple checked. I lost 5 minutes doing this over and over. I did the “no” command to delete the specific config, did a “sh run” and showed that it wasn’t there. Saved the config, and did another “sh run” to verify it was still deleted. Reconfigured again and made sure I was typing it correctly. Yup, it’s correct, alright! Did another “sh run” and a different value was showing up again from what I typed in. I was so frustrated that I wanted to click the comment button to tell Cisco what a piece $#!t the simulator was. Why can’t they just use the real IOS? Anyway, I ended up doing a ”copy start run” to restore it to the original config. That worked. I made my config and didn’t bother verifying. I was just hoping I got partial points. It’s a moot point now that I passed. But I was very frustrating and could be a difference from borderline failing or borderline passing. Hopefully those taking it in the future won’t have the same experience.  

Here’s a summary of how I prepared for the exam:

• Study materials:
• Building Scalable Cisco Internetworks (BSCI) (Authorized Self-Study Guide) (3rd Edition).
• Bits and pieces of Routing TCP/IP, Volume 1 (2nd Edition) (CCIE Professional Development).
• BGP section of Routing TCP/IP, Volume II (CCIE Professional Development)
• CCNP Building Scalable Internetworks Lab Portfolio - used sparingly. 

 

• Like I said earlier, I spent 6 months of cumulative studying, spread out in a span of close to 9 months. An advantage of this, obviously, is that it gave me a lot of time to let concepts sink in and become almost second nature. I don’t know if I would recommend this approach though. My original plan was for this to be a four-month thing, maybe 5 months at the most. With that said, I would go with 4-5 months if given the choice. Most people with a lot of experience can do it in 2-3 months.
• Study between 2-3 hours a day. When I started studying, I spent 1.5 hours in the morning (from 7am – 8:30pm) and about 1 to 1.5 hours at night (from 9:30 – 11pm). Sometime during the year, my schedule at work changed so that I could no longer study in the morning. So I went from about 8 – 11 or 9 -12 at night. And I did this almost everyday picking a day here and there to take a break.
• I created a study schedule which I followed as close as possible. This is very important in that it allowed me to track my progress and visualize where I need to be at certain points in the future. You need to be flexible with the schedule, however. Because I have a family, a job and other obligations in my community, I had to make sure I can track my progress closely and not stray away too far from my plans.
• I spent a lot of time labbing. Although I own a decent rack of routers and switches, it was much more convenient for me to use Dynagen/Dynamips. In fact you’ll find that all of the lab exercises that I have blogged about in the past were done using Dynamips. Every now and then I’d fire up the old routers and switches to blow off some dust and rust.
• During the past month of reviewing, I went to specific forums such as techexams.net and networking-forum.com and searched the forums for threads with “BSCI and fail” on them. I copied all the posts that had anything to do with people failing the exam and took notes on what particular areas people had trouble with. Not surprisingly, the big three that people mostly talked about were IPv6, Multicast, and IS-IS.
• Lastly, I blogged as much as I can about the things I was learning. I found this helped me slow my learning down a little bit and helped me think about the subjects in a more interactive way. 

There you go. I’m sure there’s much more I can write about but I’m tired. So hopefully the little bits of information I have can help others taking the exam – or compare their experiences with mine.   

Two or three of my faithful followers might be wondering where I was this past few days. Well now you know the reason for the lack of updates – been studying hard.

I am so relieved that this one is out of the way – for now. It’s been nine months since I started studying for this exam and I’m glad I passed on my first attempt. Reading from various forums about the horrors and difficulties others have had passing for the first time, I was a bit wary and at the same time confident that I was going to pass. And I did!

I’ll be celebrating tonight with the family and go out on a rare dinner at a restaurant. I’ll write up my thoughts later for those of you wondering about the test, especially those gearing up to take it soon. Laters!

Map Multicast MAC address to IP Multicast Addresses

In the course of reading through the BSCI authorize self-study guide, I’ve come across a multicast example where the author talks about the concepts behind the multicast IP to MAC address mapping.

• In order to achieve the translation between a Layer 3 IP multicast address and Layer 2 multicast MAC address, the low-order 23 bits of the IP address (Layer 3) is mapped into the low-order 23 bits of the MAC address (Layer 2).
• The high order 4 bits of the Layer 3 IP address is fixed to 1110 to indicate the Class D address space between 224.0.0.0 through 239.255.255.255
  • Ethernet MAC addresses start with 01:00:5E, allowing for a range from 01:00:5E:00:00:00 through 01:00:5E:7F:FF:FF.
• With 32 total bits present in an IP address and 4 high order bits of it set at 1110, we are left with 28 bits of unique IP addresses we can use (32 - 4 = 28).
• But remember, 23 low-order bits out of the 28 available bits are mapped to the MAC address, giving us 5 remaining bits of overlap.
• With the 5 bits of extra overlap, there are  32 (2⁵ = 32) IP multicast address that map to one MAC multicast address.

The problem is, the book does not explain or show how it solved the mapping. So I went about researching how it was done. If you happened to be studying for BSCI, I am referring to the section of the BSCI: Authorized Self-Study Guide, by Teare and Paquet, that starts on page 598 – 600.

The following is an example of how we arrive with those 32 IP addresses that map to a single MAC address:

For reference, use the following conversion chart for converting hex to binary and vice versa

Let’s start by using the example MAC address given in the book :

01:00:5e:0a:00:01

1. Convert the hexadecimal MAC address 01:00:5e:0a:00:01 to binary
   • 0000 0001 : 0000 0000 : 0101 1110 : 0000 1010 : 0000 0000 : 0000 001
   • Here’s a breakdown of the conversion bit by bit:
     
2. Isolate the 23 low-order binary bits from the converted MAC address:
   • 0000 0001 : 0000 0000 : 0101 1110 : 0000 1010 : 0000 0000 : 0000 0001
3. Take the low order 23 bits from step 2 and plug it into the low-order 23 bits of the IP address (do this in binary):
   • 1110 xxxx : x000 1010 : 0000 0000 : 0000 0000
     • 1110 -  First 4 high-order bits of the IP address for the multicast address space (224.x.x.x).
     • xxxx x - 5 remaining bits after the 23bits of the IP address is mapped to the MAC address plus the 4 high order bits 1110. This is equal to 32 total IP addresses.
4. Convert the binary equivalent of the IP addresses to decimal, replacing the x variables with all the values to get all 32 possible IP addresses:
   • 1110 0000 : 0000 1010 : 0000 0000 : 0000 0001 = 224.10.0.1
   • 1110 0001 : 0000 1010 : 0000 0000 : 0000 0001 = 225.10.0.1
   • 1110 0010 : 0000 1010 : 0000 0000 : 0000 0001 = 226.10.0.1
   • 1110 0011 : 0000 1010 : 0000 0000 : 0000 0001 = 227.10.0.1
   • 1110 0100 : 0000 1010 : 0000 0000 : 0000 0001 = 228.10.0.1
   • 1110 0101 : 0000 1010 : 0000 0000 : 0000 0001 = 229.10.0.1
   • 1110 0110 : 0000 1010 : 0000 0000 : 0000 0001 = 230.10.0.1
   • 1110 0111 : 0000 1010 : 0000 0000 : 0000 0001 = 231.10.0.1
   • 1110 1000 : 0000 1010 : 0000 0000 : 0000 0001 = 232.10.0.1
   • 1110 1001 : 0000 1010 : 0000 0000 : 0000 0001 = 233.10.0.1
   • 1110 1010 : 0000 1010 : 0000 0000 : 0000 0001 = 234.10.0.1
   • 1110 1011 : 0000 1010 : 0000 0000 : 0000 0001 = 235.10.0.1
   • 1110 1100 : 0000 1010 : 0000 0000 : 0000 0001 = 236.10.0.1
   • 1110 1101 : 0000 1010 : 0000 0000 : 0000 0001 = 237.10.0.1
   • 1110 1110 : 0000 1010 : 0000 0000 : 0000 0001 = 238.10.0.1
   • 1110 1111 : 0000 1010 : 0000 0000 : 0000 0001 = 239.10.0.1
   • 1110 0000 : 1000 1010 : 0000 0000 : 0000 0001 = 224.10.0.1
   • 1110 0001 : 1000 1010 : 0000 0000 : 0000 0001 = 225.138.0.1
   • 1110 0010 : 1000 1010 : 0000 0000 : 0000 0001 = 226.138.0.1
   • 1110 0011 : 1000 1010 : 0000 0000 : 0000 0001 = 227.138.0.1
   • 1110 0100 : 1000 1010 : 0000 0000 : 0000 0001 = 228.138.0.1
   • 1110 0101 : 1000 1010 : 0000 0000 : 0000 0001 = 229.138.0.1
   • 1110 0110 : 1000 1010 : 0000 0000 : 0000 0001 = 230.138.0.1
   • 1110 0111 : 1000 1010 : 0000 0000 : 0000 0001 = 231.138.0.1
   • 1110 1000 : 1000 1010 : 0000 0000 : 0000 0001 = 232.138.0.1
   • 1110 1001 : 1000 1010 : 0000 0000 : 0000 0001 = 233.138.0.1
   • 1110 1010 : 1000 1010 : 0000 0000 : 0000 0001 = 234.138.0.1
   • 1110 1011 : 1000 1010 : 0000 0000 : 0000 0001 = 235.138.0.1
   • 1110 1100 : 1000 1010 : 0000 0000 : 0000 0001 = 236.138.0.1
   • 1110 1101 : 1000 1010 : 0000 0000 : 0000 0001 = 237.138.0.1
   • 1110 1110 : 1000 1010 : 0000 0000 : 0000 0001 = 238.138.0.1
   • 1110 1111 : 1000 1010 : 0000 0000 : 0000 0001 = 239.138.0.1
5. All the 32 IP addresses on step 4 map to MAC address 01:00:5e:0a:00:01

Convert IP Multicast Address to Multicast MAC Address

Conversely, a multicast IP address can be converted to its equivalent MAC address. Once you’ve figured out how to convert from Layer 2 MAC to Layer 3 IP, doing the reverse is easy.

To start, we can pick any address from the 32 IP addresses we converted above. Let’s pick a random one like 227.138.0.1

1. First convert the address 227.138.0.1 to binary:
   • 11100011 : 10001010 : 00000000 : 00000001
   • We’re only concerned with the red colored portion which represents the low-order 23bits of the IP address.
     
   • Notice that we are dropping the high order bit of the second octet.
     
2. Convert those 23 bits to hexadecimal:
   • 0A:00:01
3. We already know that the first 3-bytes (24 bits) of the MAC address is 01:00:5E. This was established earlier in the article. Simply append the result on step 2 to the first 3-bytes and you have your MAC address:
   • 01:00:5E:0A:00:01
   • *You can pick any of the 32 Ip addresses we have on the list above and you will always get 01:00:5E:0A:00:01 as your MAC address following the steps just mentioned.

To summarize:

• 1^st octet – Notice that the first octet is left alone.
• 2^nd octet – You only need to convert the last 7 bits to hex. The second octet in decimal is 138. But if you drop the highest order bit, it becomes a decimal 10 or hex 0A.
• 3^rd octet – Convert it directly to hex.
• 4^th octet – Convert it directly to hex.