LAN Protocols

This page introduces the various media-access methods, transmission methods, topologies, and devices used in a local area network (LAN); to include methods and devices used in Ethernet/IEEE 802.3, Token Ring/IEEE 802.5, and Fiber Distributed Data Interface (FDDI).

A LAN is a high-speed, fault-tolerant data network that covers a relatively small geographic area. It typically connects workstations, personal computers, printers, and other devices. LANs offer computer users many advantages, including shared access to devices and applications, file exchange between connected users, and communication between users via electronic mail and other applications

Media-Access Methods

LAN protocols typically use one of two methods to access the physical network medium: carrier sense multiple access collision detect (CSMA/CD) and token passing.

In the CSMA/CD media-access scheme, network devices contend for use of the physical network medium. CSMA/CD is therefore sometimes called contention access. Examples of LANs that use the CSMA/CD media-access scheme are Ethernet/IEEE 802.3 networks, including 100BaseT.

In the token-passing media-access scheme, network devices access the physical medium based on possession of a token. Examples of LANs that use the token-passing media-access scheme are Token Ring/IEEE 802.5 and FDDI.

LAN Transmission Methods

LAN data transmissions fall into three classifications: unicast, multicast, and broadcast. In each type of transmission, a single packet is sent to one or more nodes.

1. In a unicast transmission, a single packet is sent from the source to a destination on a network.
2. A multicast transmission consists of a single data packet that is copied and sent to a specific subset of nodes on the network.
3. A broadcast transmission consists of a single data packet that is copied and sent to all nodes on the network.

LAN Topologies

LAN topologies define the manner in which network devices are organized. Four common LAN topologies exist: bus, ring, star, and tree. These topologies are logical architectures, but the actual devices need not be physically organized in these configurations. Logical bus and ring topologies, for example, are commonly organized physically as a star.

• A bus topology is a linear LAN architecture in which transmissions from network stations propagate the length of the medium and are received by all other stations.
• A ring topology is a LAN architecture that consists of a series of devices connected to one another by unidirectional transmission links to form a single closed loop. Both Token Ring/IEEE 802.5 and FDDI networks implement a ring topology.
• A tree topology is a LAN architecture that is identical to the bus topology, except that branches with multiple nodes are possible in this case.
• A star topology is a LAN architecture in which the endpoints on a network are connected to a common central hub, or switch, by dedicated links. Logical bus and ring topologies are often implemented physically in a star topology.

LAN Devices

Devices commonly used in LANs include repeaters, hubs, LAN extenders, bridges, LAN switches, and routers.

• A repeater is a physical layer device used to interconnect the media segments of an extended network. A repeater essentially enables a series of cable segments to be treated as a single cable. Repeaters receive signals from one network segment and amplify, retime, and retransmit those signals to another network segment. These actions prevent signal deterioration caused by long cable lengths and large numbers of connected devices. Repeaters are incapable of performing complex filtering and other traffic processing. In addition, all electrical signals, including electrical disturbances and other errors, are repeated and amplified. The total number of repeaters and network segments that can be connected is limited due to timing and other issues.
• A hub is a physical-layer device that connects multiple user stations, each via a dedicated cable. Electrical interconnections are established inside the hub. Hubs are used to create a physical star network while maintaining the logical bus or ring configuration of the LAN. In some respects, a hub functions as a multiport repeater.
• A LAN extender is a remote-access multilayer switch that connects to a host router. LAN extenders forward traffic from all the standard network-layer protocols (such as IP, IPX, and AppleTalk), and filter traffic based on the MAC address or network-layer protocol type. LAN extenders scale well because the host router filters out unwanted broadcasts and multicasts. LAN extenders, however, are not capable of segmenting traffic or creating security firewalls.
• Bridges analyze incoming frames, make forwarding decisions based on information contained in the frames, and forward the frames toward the destination. In some cases, such as source-route bridging, the entire path to the destination is contained in each frame. In other cases, such as transparent bridging, frames are forwarded one hop at a time toward the destination.
• Switches are data link layer devices that, like bridges, enable multiple physical LAN segments to be interconnected into a single larger network. Similar to bridges, switches forward and flood traffic based on MAC addresses. Because switching is performed in hardware instead of in software, however, it is significantly faster. Switches use either store-and-forward switching or cut-through switching when forwarding traffic. Many types of switches exist, including ATM switches, LAN switches, and various types of WAN switches.
• Routers perform two basic activities: determining optimal routing paths and transporting information groups (typically called packets) through an internetwork. In the context of the routing process, the latter of these is referred to as switching. Although switching is relatively straightforward, path determination can be very complex.

Source:netcert.tripod.com

TCP / IP - An animated discussion pt. 2

TCP / IP - An animated discussion

Cisco CCNA Certification: Broadcasts, Unicasts, And Multicasts

When you begin your CCNA studies, you get hit with a lot of different networking terms right away that you might not be familiar with. What makes it a little more confusing is that a lot of these terms sound a lot alike. Here, we're going to discuss the differences between broadcasts, multicasts, and unicasts at both the Data Link (Layer 2) and Network (Layer 3) layers of the OSI model.

A broadcast is simply a unit of information that every other device on the segment will receive. A broadcast is indicated by having every bit of the address set to its highest possible value. Since a hexadecimal bit's highest value is "f", a hexadecimal broadcast is ff-ff-ff-ff-ff-ff (or FF-FF-FF-FF-FF-FF, as the upper case does not affect hex value). The CCNA exam will demand you be very familiar with hex conversions, so if you're not comfortable with these conversions, get comfortable with them before taking the exam!

At layer 3, a broadcast is indicated by setting every bit in the 32-bit binary string to "1", making the dotted decimal value 255.255.255.255. Every host on a segment will receive such a broadcast. (Keep in mind that switches will forward a broadcast, but routers do not.) In contrast to a broadcast, a unicast is a packet or frame with only one destination.

There is a middle ground between broadcasts and unicasts, and that is a multicast. Where a broadcast will be received by all, and a unicast is received by only one host, a multicast will be received by multiple hosts, all belonging to a "multicast group". As you climb the Cisco certification pyramid, you'll be introduced to creating multicast groups and controlling multicast traffic, but for your CCNA studies you need only keep certain multicast groups in mind.

Class D addresses are reserved for multicasting this range is 224.0.0.0 - 239.255.255.255. The addresses 224.0.0.0 - 224.255.255.255 are reserved for use by network protocols on a local network segment, and like broadcasts, routers will not forward these multicast packets. (Packets with these addresses are sent with a Time To Live of 1.)

As a CCNA candidate, you should know that OSPF routers use the address 224.0.0.5 to send hellos, EIGRP routers use 224.0.0.10 to send updates, and RIP version 2 uses 224.0.0.9 to send routing updates. RIP version 1 and IGRP both broadcast their updates.

Multicasting gets a bit more complicated as you go from your CCNA to the CCNP and CCIE, but by simply understanding what multicasting is, you go a long way toward securing the CCNA.

Source : http://EzineArticles.com

Studying CCNA CBT Courses and Getting Your Foot Through the Door

If you want to pursue a career in network administration, then you'll need to become a Cisco Certified Network Associate. You can do this by taking a CCNA CBT course and then passing the exam. This exam is designed for entry level network administrators, who are then rewarded with their certificates upon passing.

In addition to receiving the certification, entry level Associates also need some training and experience. You can receive your training online through watching a series of CCNA training videos. You can take the knowledge that you receive from the training courses and videos and then begin practicing. By practicing, you can get some hands on experience that will come in handy for your career.

One way you can practice with what you learn from your CCNA CBT course is by using simulators. Don't depend on them completely, though. You still need to get some actual hands on experience whenever you can. Any kind of real experience will look good on your job resume. If you want to work as a freelance administrator then you'll still need to know what you're doing before providing your services to clients.

It's a good idea to watch as many CCNA training videos that you can. You'll actually be able to see, step by step, everything that you'll need to practice doing yourself. Another way you can begin practicing is by buying up all the used routers and any other equipment you can find. Just as an artist or a writer keeps a portfolio to show to potential clients, you should as well.

Sometimes CCNA CBT course and class instructors go the extra mile in helping students they are impressed with. Try proving yourself and your worth not only as a promising student, but as an up and coming network administrator as well. Let your instructors know that you mean business, and that you're taking your lessons seriously. Study all the material your course presents you with, and more. Make sure you know everything like the back of your hand.

Keep in mind that there are other computer courses out there, along with CCNA CBT. While being a Cisco Certified Network Associate is very rewarding, you should also study other courses as well. The more you understand about computers and technology, the better. By having other certifications, you'll be increasing your chances of getting your foot through the door, and before you know it, you'll be successful!

Source: http://EzineArticles.com

CCNA / CCNP Home Lab Tutorial: Assembling Your Cisco Home Lab

A CCNA or CCNP candidate who wants to be totally prepared for their exams is going to put together a home lab to practice on. With used Cisco routers and switches more affordable and plentiful then ever before, there's really no excuse to not have one!

With the many different models available, there is some understandable confusion among future CCNAs and CCNPs about which routers to buy and which ones to avoid. You can take almost any set of Cisco routers and put together a home lab; part of the learning process is taking what equipment you have available and putting together your own lab! For those of you preparing to start your home lab or add to your existing one, this article will list the routers I use in my Cisco pods. You certainly don't have to have all this equipment, but this will give you some good ideas on how to get started.

The most versatile router you can get for your CCNA / CCNP home lab is a 2520. These routers come with four serial ports, one ethernet port, and one BRI interface for ISDN practice. This mix of interfaces means you can actually use it as a frame relay switch while using the ethernet and BRI ports for routing. (There is no problem with using a lab router as both your frame relay switch and a practice router; for a frame relay switch sample configuration, visit my website!)

My pods consist of five routers and two switches, and three of the five routers are 2520s, due to their versatility. A recent ebay search showed these routers selling for $99 - $125, an outstanding value for the practice you're going to get.

I also use 2501s in my home labs. These have fewer interfaces, but the combination of two serial interfaces and one ethernet interface allows you to get plenty of practice.

A combination that works very well is using three 2520s; one as my dedicated frame relay switch, one as R1, and another as R2. Add a 2501 as R3, and you can have a frame cloud connecting R1, R2, and R3, a direct serial connection between R1 and R3, an Ethernet segment that includes all three routers, and an ISDN connection between R1 and R2 if you have an ISDN simulator. That combination will allow you to get a tremendous amount of practice for the exams, and you can always sell it when you're done!

2501s are very affordable, with many in the $50 range on ebay. It's quite possible to get three 2520s and one 2501 for less than $500 total, and you can get most of that money back if you choose to sell it when you're done.

With four routers to work with, you're probably going to get tired of moving that console cable around. An access server (actually a Cisco router, not the white boxes we tend to think of when we hear "server") will help you out with that. An access server allows you to set up a connection with each of your other routers via an octal cable, which prevents you from moving that console cable around continually. For an example of an access server configuration, just visit my website and look in the "Free Training" section.

Access server prices vary quite a bit; don't panic if you do an ebay search and see them costing thousands of dollars. You do NOT need an expensive access server for your CCNA / CCNP home lab. 2511s are great routers to get for your access server.

One question I get often from CCNA / CCNP candidates is "What routers should I buy that I can still use when I'm ready to study for the CCNP?" The CCIE lab changes regularly and sometimes drastically when it comes to the equipment you'll need. During my CCIE lab studies, I found that renting time from online rack rental providers was actually the best way to go. Don't hesitate when putting your CCNA / CCNP home lab together, wondering what will be acceptable for the CCIE lab a year or so from now. None of us know what's going to be on that equipment list, so get the CCNA and CCNP first - by building your own Cisco home lab!

Source: http://EzineArticles.com

Cisco CCNA Exam

This article will give advice on taking the Cisco CCNA Test which will hopefully give you the confidence to successfully pass.

In your preparation for the CCNA test have in mind that passing the exam is but the beginning of the journey. The CCNA certification curriculum will give you a sure foundation to build for other higher Cisco certificates. Do not have the mindset of fear but but say to yourself "I can pass this exam". Tell yourself that you will conquer the exam. You will serve yourself well and follow Cisco's advice by taking the Interconnecting Cisco Networking Devices Part 1 (ICND1) v1.0 and the Interconnecting Cisco Networking Devices Part 2 (ICND2) v1.0 courses. Use your favorite search engine and type in the ICND course. For example, if you live in Belgium type " ICND2 courses in Belgium". Cisco also has resources for searching courses. Type in LPCM in your search engine. Some courses also attract a 250-dollar Amazon.com Gift certificate for free.

Not everybody prepare for exams in the same way because there is a sense of uniqueness about us. How boring and dull would it be if we were all the same. Even robots can be created with a sense of uniqueness and difference through artificial intelligence. The point is, for a person to achieve the end goal is not always followed in the same fashion. Vendor specific qualifications like the CCNA however, has set topics which need to be studied in order to pass the CCNA test. How you go about studying them is entirely up to you but make sure you do concentrate on them. These are the general guideline topics which Cisco recommends:

Describe how a network works Configure, verify and troubleshoot a switch with VLANs and interswitch communications Implement an IP addressing scheme and IP Services to meet network requirements in a medium-size Enterprise branch office network. Configure, verify, and troubleshoot basic router operation and routing on Cisco devices Explain and select the appropriate administrative tasks required for a WLAN Identify security threats to a network and describe general methods to mitigate those threats Implement, verify, and troubleshoot NAT and ACLs in a medium-size Enterprise branch office network. Implement and verify WAN links

Each of the above topics carry sub-topics and these are what needs to be digested. A useful way to master these sub-topics before you take the CCNA Exam is to write down in your own words on a A4 piece of paper the requirement. For example, Configure, verify and troubleshoot a switch with VLANs and interswitch communications and sub-topic - Explain network segmentation and basic traffic management concepts - you would do what is says on a A4 paper. This exercise would reinforce your knowledge and understanding of the subject matter. This will also enable you to pass the CCNA exam with flying colors.

After taking the CCNA test you will find that a pass is a pass and a fail is a fail but with percentage. There is no option to go back on a question once you click 'Next. You cannot go back to previous questions you have to move forward. You will do more damage to yourself if you do not answer a question and move on than if you were to answer the wrong question. So it pays to answer every question since the total score is accumulative. As Captain Kirk said to Mr. Spock in Star Trek, take your best guess. Mr. Spock does not make guesses but if he had to this would be more accurate than most people's best knowledge statement.
Ah! For us then, study hard so you don’t have to guess.

There are a number of aides to help you in your journey to pass the CCNA Test. First there is the mention of Ciscopress documentation. Ciscopress are generally well written by Cisco Certified Internetworking Experts (CCIE). Just to note, CCIE's gave up their social life to achieve their highly recognized status and is the best example of study, study, study and more study. These people are the 'cream of the crop' in networking but more on that in another article. As well as Ciscopress books there are also other reputable publishers that have contributed immensely to Cisco CCNA curriculum. Here follows are a listing of books as recommended by Cisco and then non Ciscopress literature.

There are two CCNA paths at present:
CCNA 640-801 and CCNA 640-802 where the former exam track expires in November 2007. You can read further information on the two exams in CCNA Certifications article at the website below.

CCNA 640-801:
CCNA 640-801 Titles
Learn: CCNA Portable Command Guide
Learn: CCNA Self-Study: Interconnecting Cisco Network Devices (ICND)
Learn: CCNA Self-Study: Introduction to Cisco Networking Technologies (INTRO)
Learn: CCNA Preparation Library
Experience: CCNA Video Mentor
Experience: Cisco CCNA Network Simulator
Prepare: CCNA ICND Exam Certification Guide
Prepare: CCNA INTRO Exam Certification Guide
Prepare: CCNA Official Exam Certification Library, Second Edition
Practice: CCNA Flash Cards and Exam Practice Pack

CCNA 640-802:
CCNA 640-802/CCENT 640-822 Titles
Learn: CCNA Portable Command Guide, Second Edition
Experience: CCNA Video Mentor
Prepare: CCENT/CCNA ICND1 Official Exam Certification Guide, Second Edition
Gain early access to the contents of this book with the Rough Cut edition on Safari.
Prepare: CCNA ICND2 Exam Certification Guide, Second Edition
Gain early access to the contents of this book with the Rough Cut edition on Safari.
Prepare: CCNA Official Exam Certification Library, Third Edition
Practice: CCNA Flash Cards and Exam Practice Pack, Third Edition
Practice: CCNA Quick Reference Sheets: Exam 640-802
Practice: CCENT Quick Reference Sheets: Exam 640-822

The CCNA 640-802 has just become available in 2007 so there is limited content. As the course develops this document will be updated to include the latest literature so please bookmark this page

So you are ready to take the CCNA test. Go with full confidence knowing that you have studied hard and pass that exam. The fee for appearing in the CCNA examination is about $125-$150 per sitting. In the UK the price for taking the exam is approx £90 per sitting. Good success!

Be sure to check out other articles such as CCNA Bootcamp (this can list all available tools for CCNA), CCNA Salaries, CCNA Certifications

Source: http://EzineArticles.com

How to pass CCNA: 6 Steps to Success

CCNA is one of the most respected Associate level Certification in the world today.
Getting a CCNA will definitely help you to get a better job or at least get your foot into Professional Networking Field. When you meet a person that has CCNA degree you will notice that he or she knows something about Networking.
This article will describe and give you some tips on how to achieve CCNA.
I did it so can you, so lets get started.


• 1. Getting ready mentally:
  First thing you need to do is mentally prepare your self. What I mean by that is that you have to seriously think about on why are you getting CCNA and why do you want to be CCNA certified. You have to firmly decide and believe that you will get CCNA within next 3-6 months or so.
  Try to budget your study time well. If you a very social person (like me) you will have to give up some of your social time for the next couple of months.
  Your friends and family will understand. Trust me: it is well worth it. Once you get that cert you can make up for the lost social time.
  
  
• 2. Getting the right study material:
  Second thing you need to do is to get proper study material.
  There is lot of controversy around this and some people go overboard with study guides, books, simulators and such.
  I believe that two Cisco Press books INTR and ICND by Wendell Odom are enough as far as the books go. They are really well written and easy to follow. So sign up at http://www.ciscopress.com and get those two books. Make sure you got the latest version.
  You will also want to get some kind of a simulator that will let you practice commands and that will also build up your confidence.
  You can buy real equipment but that could get expensive. I highly recommend that you become member of Cisco Certification forum.
  Forum is huge and you will get lot of helpful answers, tips and advices pretty quick. (I know I did)
  
  
• 3. Approach and diving deep:
  There are many different approaches to studying from books but I will tell you about mine. This step will take the most of your studying time.
  -Before you even start reading any of the books I suggest learning binary math (really easy) and subnetting so you can do it in your sleep.
  http//www.learntosubnet.com is excellent resource. -read both books casually once from front to cover (make sure you cover introduction and practice questions too). This will give you good overview.
  -Install both CD’s that came with books and practices some of the questions. Don’t worry if you get lot of them wrong.
  -Now, you will ready both books again but this time you will have to read it to truly understand the concept and how things work. Master one chapter and do questions from just that chapter until you sick of it. Then move to the next chapter.
  -Once you mastered all chapters do lot of questions and labexercises. Those two CD’s will give you ability to do that.
  
  4. Schedule the test:
  You’re not done yet with studying but it is really good to schedule the test after you completed step 3 in this article. Here is why:
  If you schedule the test a month in advance right after you completed step 3, you won’t be able to slack and make excuses not to study hard until tests and it is also good to give your self a headline. I have seen people working on their CCNA for 2 years. They master one or two chapters, then they rest for 2 two months and right when they think they are ready for the next chapter, they forget what they have learned in the first chapter.
  
  5. Read both books one more time to refresh.
  This is optional, but I highly recommend reading the both books one more time. If you read both books in a three week that will give you one more week before the test to cram which is subject of the next step.
  So by now you should’ve read both books three times over. I also suggest re-reading questions and answers from both books one more time.
  
  6. Cram, Cram and Cram -This is the last part of your study and there is no turning back. Deadline is hanging around your neck like a noose. You should cram Q&A for no more then 10 days before you take the test.
  At this point it is really important that you get fresh and different questions then those included with your CD’s. Some people claims that brain dumps or Q&A are bad and evil. I tend to disagree with that. At this point you already firmly grasped the whole CCNA concept and Q&A will only help you. So get some Q&A exam question and cram, cram and cram them for a week.
  Don’t use books or CD’s anymore. There is no looking back. No worries, material from the books will return to you at the right time.
  -Don’t do any studying a night or a day before the test. Go out with your wife or significant other to a dinner and a movie. Relax. It is very important to relax and get a good night sleep since one of those testing boots could really be intimidating. If you did all the steps above and read books with intention to understand the topics and how stuff works (no pun intended), and not just to pass the test you should be more then ready by now.
  
  We came to an end of this short tutorial. I hope this article give you at least some ideas on how to approach studying for CCNA.
  If you fail CCNA first time, don’t get discouraged. You will have more knowledge and confidence when you attempt it the next time then the person who passed it on the first try. Whatever approach you take I wish you good luck and prosper career.
  
  

Source : http://EzineArticles.com

How To Become A True CCNA

The field will always need qualified CCNAs. The key word is "qualified". How can you make sure you're truly qualified? It's actually pretty simple.

1. Use routers and switches in your study, not simulators. Simulators are OK to start with, but when you're in the interview room and you're taken to the network room, that simulator's not going to be there. Real routers and switches are. With all due respect to the simulators on the market, they're not routers and switches. Don't fool yourself.

Attend a CCNA class that gets you plenty of time on real Cisco equipment. Used Cisco equipment is cheaper than ever. Look at it this way -- you can put together a true CCNA lab that you can also use for CCNP study for less than $1000. When you choose to sell it, you can get half of that back. A small investment like that pays huge dividends in your future.

2. Know binary math. Some leading CCNA books tell you to just memorize a chart to get by the exam. I wish I had a nickel for every CCNA that hasn't been able to solve a simple subnetting problem in a job interview. Someone who doesn't know binary math is not going to go far. Who's going to remember that chart they memorized for the exam six months ago?

3. Run plenty of "show" and "debug" commands when running labs. These are the commands that show you what's going on "behind the command". You need to know what is really happening when you put in a command when you get asked about it in an interview.

These three simple points separate the real CCNAs from the ones who got lucky or braindumped their way to success. By constructing a solid foundation of Cisco knowledge at the CCNA level, you build the bridgework for a lifetime of career success. You don't have to have a lot of job experience to get a CCNA job, but you do have to really understand the subject matter.

Source : http://EzineArticles.com

Cisco's New CCNA Voice Specialization Can Increase Your Pay

Are you looking to boost your career or have more job security? If so, Cisco's newest CCNA Voice specialization may be the right step for you. This past summer, Cisco released three new certifications:

• CCNA Voice
• CCNA Security
• CCNA Wireless

These exams are add-on concentrations to Cisco's very popular Cisco Certified Network Associate (CCNA) certification. For many years the CCNA has been the most sought-after entry level computer networking certification in the industry which focuses mostly on Router and Switch configuration.

What are some of the key motivators for getting the CCNA Voice certification? Based on research by Forrester Consulting the demand for specialized IT professionals will be very strong in the coming years. One finding was that 69% of the companies surveyed expect to have a dedicated voice technologies specialist in their organization within five years. Another motivator is salary. Certification Magazine's 2007 annual salary survey found a worldwide average salary of US$74,810 for people with a CCNA certification. In comparison, attaining the professional-level Cisco Certified Voice Professional (CCVP) certification beyond the CCNA resulted in a 23 percent higher salary, at an average of US$92,350. Job roles available for individuals who obtain a CCNA Voice certification include:

• Voice Administrators
• Voice Technicians
• Voice Engineers

The CCNA Voice concentration provides candidates with a good foundation in traditional telephony and Cisco Unified Communications. The exam focuses on testing a student's knowledge to install, configure and support a Cisco Unified Communications solution from 8 - 250 phones. In order to attain the certification there are two routes a candidate can go:

Option 1

Pass the three following exams:

1) Interconnecting Cisco Networking Devices (640-822 ICND1)
2) Interconnecting Cisco Networking Devices (640-816 ICND2)
3) Implementing Internet Unified Communications (640-406 IIUC)

Option 2

Pass the two following exams:

1) Cisco Certified Network Associate (640-802 CCNA)
2) Implementing Internet Unified Communications (640-406 IIUC)

Having the CCNA Voice is a new a requirement for achieving the Cisco Certified Voice Professional (CCVP). The one caveat is if you have already passed the CCNA you will have until June 2009 to pass the CCVP without taking the CCNA Voice.

If you are interested in getting your CCNA Voice specialization or just want to learn more about Cisco and Microsoft Unified Communications please sign up for our free newsletter at http://www.voip-tutor.com

Get a free "Introduction to Cisco Unified Communications" video tutorial!

http://www.voip-tutor.com/freetutorial.htm

Source : http://EzineArticles.com

CIW Certification Courses For Focused IT Specialists

CIW certification courses also known as the Certified Internet Web Professional program is a vendor-neutral Internet certification program. It is a Web Technology standard that is a number of governments, businesses and academic institutions are adopting today. The core curriculum of CIW focuses on several standards like web design, networking, security and administration.

The Need For Synergists

Today with increasing progressive changes taking place in the IT industry, specialists are being replaced by synergists. IT synergists are specialists that have a broader skill set. Their set of skills includes handling interdependent systems like integrating, designing and troubleshooting. And for gaining such skills it is very important to acquire people with varied experience and multidiscipline knowledge.

The above need is met by CIW certification courses. Such courses hone the skills of professionals and turn them into IT synergists that have the best knowledge of the industry standards.

Benefits Of CIW Certification

Professional CIW certification courses can help one master today's technology driven world and achieve their career goals. Some more benefits of becoming a CIW professional are:

- Inclusion of industry-recognized credentials to the resume.
- Specialized and defined job role skills.
- A jump in the salary structure and increased job responsibilities.
- A sharp advancement within the organization.
- A different category than the co-workers.
- Pathway to up-to-date skills and knowledge in the fast evolving technology world.

Several students have experienced a rise in their career after successful completion of their CIW certification courses. If you too wish to gain a competitive edge over your competitors then enroll for a CIW course today. These courses are beneficial both for employers and employees. For employees, these courses act as the direct gateway to several career opportunities. For organizations and employers, CIW certification helps reduce hiring and training related costs thus creating a skilled workforce within the company itself.

CIW Certification Exams And Courses

There are several CIW certification courses to choose from. For beginners there are foundational CIW Associate certification programs and for advanced learners there are CIW Professional certifications and advanced-level Master certification programs.

Some commonly sought after CIW certification courses are:

- CIW Associate: For gaining basic hands-on skills and knowledge for Internet professionals. It includes basic knowledge of network infrastructure, Internet technologies and Web authoring.
- CIW Associate Design Specialist: A certification pathway for Web design students with two popular CIW courses combines into one.
- CIW Professional: Those who have already earned an Associate certification can attain a CIW Professional certification.
- Master CIW Designer: Certification for a successful career as a Web designer, Web marketing specialist, Creative director or e-commerce developer.
- CIW Database Design Specialist: A new certification program that enables gaining knowledge of database design principles, theory and their application.
- Master CIW Administrator: For professionals who are interested in a career in intranet administration or networking system.
- CIW Security Analyst: The job of a security analyst is to protect an organization's assets and operations. The certification course is allowed to those who have already earned a Master CIW Administrator certification.
- Master CIW Web Site Manager: Helps the student gain a cross-functional set of Web skills that would help take up the role of a Web manager.
- Master CIW Enterprise Developer: Helps professionals develop enterprise web-enabled applications and implement the same to e-business solutions.

Source : http://EzineArticles.com

CCNA -The Door to the Best Networking Careers

The CCNA (Cisco Certified Network Associate) certification is an entry level certification for networking professionals. It is the first step to higher level certifications, such as Cisco Certified Network Professional (CCNP) and Cisco Certified Internet work Expert (CCIE) certification.

The CCNA certification is the best option for the computer net workers, field technicians, IT helps desk engineers, and other professionals of IT associated with controlling the computer networking process. This certificate is considered as the basic qualification for installing, operating, configuring and troubleshooting a mid-sized switched and routed network. A CCNA certified professional is considered to be trained in working with a networking environment that includes a group of switched networks. In simple terms, the CCNA certified professional is able to manage a host of computer routed networks connected through switches.

With the increasing demand for networking specialists, the value of the CCNA certification is also going up in the IT industry's job market. This certification is considered to be a benchmark for sorting out the best and the most efficient technicians in the field of network management. The CCNA is offered on the basis of a test that is conducted by Cisco. The examination is structured by emphasizing on the questionnaire that has drag and drop options, multiple choice single answers, multiple choice multiple answers, simulations and fill in the blank type of questions. However, although the structure seems to be simple, professional training and guidance is required to be successful in the exams. As is obvious, the nature of the examination is purely technical and special knowledge of the networking environments and solutions are required to pass in the test. Therefore, the best option for getting certified is to take help of professional experts. There are several institutions that focus on CCNA examination training from where one can get adequate support and guidance.

To get CCNA certification, one requires specialized knowledge in the fields of installation, configuration, design, troubleshooting, and maintenance and management of networks. As a matter of fact, the CCNA examination training focuses on these aspects of networking in great detail. A potential candidate applying for CCNA certification is also trained in practical networking environment so that once he/she gets certified and starts working, he/she faces no problem in handling the IP or non IP networks. As practical knowledge is what matters the most, the examination is also based upon this specific aspect. It is wrong to believe that without having any specialized knowledge, one can get certified. As mentioned earlier, since it is considered to be a benchmark for the networking professionals, the exams take care of the minute details as well as proficient knowledge of the candidates. Therefore, those who get certified are necessarily the best in the field of network management and administration.

In the competitive market of networking jobs, it is crucial to have specialized knowledge and professional certification. The CCNA certification is accepted and recognized all over the world. Therefore, it definitely adds value to the credentials of the candidates looking for a suitable job in networking. Moreover, the examination is also used as a tool for sorting out the best networking professionals who would be responsible for the management and maintenance of the networking environments.

Today, some say that the CCNA certification is the best tool to shape up the networking career.

Source :http://EzineArticles.com

Cisco CCNA Certification: Becoming A Truly Valuable CCNA

The CCNA is an exciting beginning to your Cisco career, but just having the certification simply isn't enough. A recruiter or interviewer isn't going to be impressed just with the cert; you've got to have some real-world knowledge to back it up.

I've been down that road myself, and sat on both sides of the CCNA job interview table. With that in mind, I'd like to offer to you some tips on becoming a truly valuable and employable CCNA.

Get some hands-on experience. I know the trap well; you can't get experience until you get a CCNA, and you can't get a CCNA without real experience. Well, actually, you can, but do you want to? Working on simulators is fine to a certain extent, but don't make the classic mistake of depending on them. I've seen plenty of CCNAs who were put in front of a set of routers and really didn't know what to do or how to put together a simple configuration, and had NO idea how to begin troubleshooting.

There are CCNA classes that offer you the chance to work with industry experts on real Cisco equipment. Beyond that, you can put together your own CCNA rack for less than $1000 by buying used routers. Some people think that's a lot of money, but this is the foundation of your career. Treat it that way. The work you do now is the most important work you'll ever do. Do it on real Cisco equipment. The skills I learned as a CCNA helped me all the way up to the CCIE.

Besides, after you get your CCNA (and after that, hopefully you'll choose to pursue the CCNP), you can always get some of your money back by selling the equipment. The hands-on experience you gain this way is invaluable.

Know binary math. Do NOT go the easy route of memorizing a subnet mask chart for the CCNA exam. I know some people brag about being able to pass the CCNA exam without really understanding binary math. I've seen those people on the other side of the interview table, and they're not laughing when I ask them to do a subnetting question. They're not laughing when they can't explain or create a VLSM scheme. That chart does nothing to help you understand what's going on.

If you can add and know the difference between a one and a zero, you can do binary math. Don't let the name intimidate you. Become a REAL CCNA -- learn binary math !

Run "show" and "debug" commands. No commands help you truly understand how things work in a Cisco network than show and debug commands. As you progress through the Cisco certification ranks, you'll be glad you started using these at the CCNA level.

Do you need to know these commands for the exam? Probably not. Do you need them to be successul in the real world? Absolutely.

The Cisco certification track has been great to me, and it can boost your career as well, whether you stop at the CCNA, CCNP, or go all the way to the CCIE. It's the skills you develop today that will truly make you a networking engineer. Don't take shortcuts or get the attitude of "just passing the exam".

It's what you achieve after the exam that counts, and it's the work you put in before passing the exam that makes those achievements possible.

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of over 100 free certification exam tutorials, including Cisco CCNA certification test prep articles. His exclusive Cisco CCNA study guide and Cisco CCNA training is also available!

Visit his blog and sign up for Cisco Certification Central, a daily newsletter packed with CCNA, Network+, Security+, A+, and CCNP certification exam practice questions! A free 7-part course, "How To Pass The CCNA", is also available, and you can attend an in-person or online CCNA boot camp with The Bryant Advantage!

Source : http://EzineArticles.com

Cisco CCNA Certification and Career Path

Following your computer training toward your career path, you can go for the CCNA certification (Cisco Certified Network Associate), which indicates a foundation in the apprentice knowledge of networking. CCNA training allows you the ability for installations and operation of LAN, WAN, and dialup access services for small networks with 100 nodes or less.

The CCNA course includes, but not limited to use the different networking protocols such as Ethernet, Access Lists, Serial, IP, IGRP, Frame Relay, IP RIP, and VLANs. Cisco's CCNA Prep Center Pilot offers simulations and sample questions, besides the e-learning modules and laboratories.

Computer training includes also valuable tips from CCNA professionals, in addition to expert advice, and encouragement through CCNA certification success stories. CCNA training does not require any prerequisite and makes available many other resources to help students with the preparation of their CCNA certification exams.

CCNA course, exams and recommended training include the Introduction to Cisco Networking Technologies (INTRO), the Interconnecting Cisco Networking Devices (ICND) or both. CCNA training and additional training, probably cover most of your career path expectations.

However, Cisco's CCNA certifications are valid for 3 years, so it is necessary for additional computer training to re-certify. This is achieved by either passing the current CCNA exam at the moment of the original certification's expiration, passing the ICND exam, passing the 642 professional levels.

After CCNA training your can also re-certify by passing the Cisco Qualified Specialist exam, excluding the Sales Specialist exams, or passing a CCIE written exam, which is a re-certify form valid for individual who had a CCNA certification starting from October 1, 2004.

Cisco CCNA online training certification program, offers the same value, knowledge and skill earned on a traditional CCNA course, and it is a nationally recognized certification. With computer training online, you will gain knowledge of switched LAN Emulation networks, which are made up of Cisco original equipment.

CCNA training online focuses the coverage of Cisco router configuration procedures, mapped to exam objectives in order to prepare you for Cisco Exam 640-80, in partnership with major universities and colleges offering as well CCNA certification.

The Computer training program online consists of 2 sections; "Introduction to Network Engineering", allowing the student to understand the world of network engineering, learning fundamental facts of data network theory and current technologies making the Internet tick.

The second section of the online CCNA course, "Practical Network Engineering", is an approach to some of the most powerful networking technologies, involving extensive work on switches, Cisco routers, and firewalls in a simulated network environment, preparing students to earn the CCNA certification.

Natalie Aranda writes about computer and IT training. Computer training includes also valuable tips from CCNA professionals, in addition to expert advice, and encouragement through CCNA certification success stories. CCNA training does not require any prerequisite and makes available many other resources to help students with the preparation of their exams.CCNA certificatio

Source :http//EzineArticles.com

EtherChannel configure mode with PAgP

PAgP facilitates the automatic creation of EtherChannel links by exchanging packets between channel-capable ports. The protocol learns the capabilities of port groups dynamically and informs the neighboring ports.
After PAgP identifies correctly paired channel-capable links, it groups the ports into a channel. The channel is then added to the spanning tree as a single bridge port. A given outbound broadcast or multicast packet is transmitted out one port in the channel only, not out every port in the channel. In addition, outbound broadcast and multicast packets transmitted on one port in a channel are blocked from returning on any other port of the channel.

There are four user-configurable channel modes: on, off, auto, and desirable. PAgP packets are exchanged only between ports in auto and desirable mode. Ports configured in on or off mode do not exchange PAgP packets. For switches to which you want to form an EtherChannel, it is best to have both switches set to desirable mode. This gives the most robust behavior if one side or the other encounters error situations or is reset. The default mode of the channel is auto. Both the auto and desirable modes allow ports to negotiate with connected ports to determine if they can form a channel. The determination is based on criteria such as port speed, trunking state, and native VLAN. Ports can form an EtherChannel when they are in different channel modes as long as the modes are compatible. This list provides examples:

• A port in desirable mode can successfully form an EtherChannel with another port
  that is in desirable or auto mode.
• A port in auto mode can form an EtherChannel with another port in desirable
  mode.
• A port in auto mode cannot form an EtherChannel with another port that is also in
  auto mode, since neither port initiates negotiation.
• A port in on mode can form a channel only with a port in on mode because ports
  in on mode do not exchange PAgP packets.
• A port in off mode cannot form a channel with any port.
• Only the combination auto-desirable, desirable-desirable and on-on will allow a channel to be formed.
  

EtherChannel can be

• Ports in the channel can only be assigned to one VLAN
• Ethernet channels can be set up for fast Ethernet, Gigabit Ethernet, and 10 Gigabit
  Ethernet.
• Ethernet channels can indeed be set up as trunks.
• Ports within a Fast Ether Channel need to have identical duplex and speed
  settings.
• Port Aggregation Protocol (PAGP) facilitates the automatic creation of Fast Ether
  channels links.

The PAgP modes are explained below.

• Off: PAgP will not run. The channel is forced to remain down.
• Auto: PAgP is running passively. The formation of a channel is desired; however, it is not initiated.
• Desirable: PAgP is running actively. The formation of a channel is desired and initiated.
• On: PAgP will not run. The channel is forced to come up.

source :http://www.cisconet.com

Link aggregation

Link aggregation or IEEE 802.1AX-2008, is a computer networking term which describes using multiple network cables/ports in parallel to increase the link speed beyond the limits of any one single cable or port, and to increase the redundancy for higher availability.

Most implementations now conform to what used to be clause 43 of IEEE 802.3-2005 Ethernet standard, usually still referred to by its working group name of "IEEE 802.3ad". The Link Aggregation definition has since been moved to a standalone IEEE 802.1AX standard.

Other terms for link aggregation include "Ethernet trunk", "NIC teaming", "port channel", "port teaming", "port trunking", "link bundling", "EtherChannel", "Multi-Link Trunking (MLT)", "NIC bonding", "Network Fault Tolerance (NFT)".

Link Aggregation between a switch and a server

Description

Link aggregation is designed to overcome two problems with Ethernet connections: bandwidth limitations and lack of redundancy.

The first issue is that bandwidth requirements do not scale linearly. Ethernet bandwidths historically have increased by an order of magnitude each generation (10 Megabit/s, 100 Mbit/s, 1000 Mbit/s, 10000 Mbit/s). If one started to bump into bandwidth ceilings, then the only option was to move to the next generation which could be cost prohibitive. An alternative solution, introduced by many of the network manufacturers in the early 1990s, is to combine two physical Ethernet links into one logical link via channel bonding. Most of these solutions required manual configuration and identical equipment on both sides of the aggregation.^[1]

The second problem is that there are three single point of failures in a typical port-cable-port connection. In either the usual computer-to-switch or in a switch-to-switch configuration, the cable itself or either of the ports the cable is plugged into can fail. Multiple physical connections can be made, but many of the higher level protocols were not designed to failover completely seamlessly.

IEEE Link Aggregation

Standardization process

By the mid 1990s, most network switch manufacturers had included aggregation capability as a proprietary extension to increase bandwidth between their switches. However, each manufacturer developed their own method which led to compatibility problems. The IEEE 802.3 group took up a study group to create an inter-operable link layer standard in November 1997 meeting.^[1] The group quickly agreed to include an automatic configuration feature which would add in redundancy as well. This became known as "Link Aggregation Control Protocol".

Initial release 802.3ad in 2000

Most gigabit channel bonding is now based IEEE standard of Link Aggregation which was formerly clause 43 of the IEEE 802.3 standard added in March 2000 by the IEEE 802.3ad task force.^[2] Nearly every network equipment manufacturer quickly adopted this joint standard over their proprietary standards.

Move to 802.1 layer in 2008

It had been noted that certain 802.1 layers (such as 802.1X security) were positioned in the protocol stack above Link Aggregation which was defined as an 802.3 sublayer.^[3] This discrepancy was resolved with formal transfer of the protocol to the 802.1 group with the publication of IEEE 802.1AX-2008 on on 3 November 2008.

Link Aggregation Control Protocol

The Link Aggregation Control Protocol (LACP) is included in the IEEE specification as a method to control the bundling of several physical ports together to form a single logical channel. LACP allows a network device to negotiate an automatic bundling of links by sending LACP packets to the peer (directly connected device that also implements LACP).

Advantages over static configuration

• Failover when a link fails and there is (for example) a Media Converter between the devices which means that the peer will not see the link down. With static link aggregation the peer would continue sending traffic down the link causing it to be lost.
• The device can confirm that the other end is configured for link aggregation. With Static link aggregation a cabling or configuration mistake could go undetected and cause undesirable network behavior. ^[4]

Practical notes

LACP works by sending frames (LACPDUs) down all links that have the protocol enabled. If a device is present on the other end of the link that also has LACP enabled, it will also independently send frames along the same links enabling the two units to detect multiple links between themselves and then combine them into a single logical link. LACP can be configured in one of two modes: active or passive. In active mode it will always send frames along the configured links. In passive mode however, it acts as "speak when spoken to", and therefore can be used as a way of controlling accidental loops (as long as the other device is in active mode). ^[5]

Usage

Network backbone

Link aggregation is an inexpensive way to set up a high-speed backbone network that transfers much more data than any one single port or device can deliver. Although, in the past, various vendors used proprietary techniques, the preference today is to use the IEEE standard, which can either be set up statically or by using the Link Aggregation Control Protocol (LACP). This allows several devices to communicate simultaneously at their full single-port speed while not allowing any one single device to monopolize all available backbone capacity.

This has limitations: originally, link aggregation was developed to provide redundancy, and not bandwidth benefits. The actual benefits vary based on the load-balancing method used on each device (different balancing algorithms can be configured at each end and this is actually encouraged to avoid path polarization).

The most common way to balance the traffic is to use L3 hashes. These hashes are calculated when the first connection is established and then kept in the devices' memory for future use. This effectively limits the client bandwidth in an aggregate to its single member's maximum bandwidth per session. This is the main reason why 50/50 load balancing is almost never reached in real-life implementations; around 70/30 is more usual. More advanced distribution layer switches can employ an L4 hash, which will bring the balance closer to 50/50.

Link aggregation also allows the network's backbone speed to grow incrementally as demand on the network increases, without having to replace everything and buy new hardware.

For most backbone installations it is common to install more cabling or fiber optic pairs than are initially necessary, even if there is no immediate need for the additional cabling. This is done because labor costs are higher than the cost of the cable, and running extra cable reduces future labor costs if networking needs change. Link aggregation can allow the use of these extra cables to increase backbone speeds for little or no extra cost if ports are available.

Efficiency of equipment

Aggregation becomes inefficient beyond a certain bandwidth depending on the total number of ports on the switch equipment. A 24-port gigabit switch with two 8-gigabit trunks is using sixteen of its available ports just for the two interswitch connections, and leaves only eight of its 1-gigabit ports for other devices. This same configuration on a 48-port gigabit switch leaves 32 1-gigabit ports available, and so it is much more efficient (assuming of course that those ports are actually needed at the switch location).

When 40-50% of the switch ports are being utilized for backbone trunking, upgrading to a switch with either more ports or a higher base-operating speed may be a better option than simply adding more switches, especially if the old switch can be re-used elsewhere on a less performance-critical part of the network.

Use on network interface cards

Network interface cards (NICs) can also sometimes be trunked together to form network links beyond the speed of any one single NIC. For example, this allows a central file server to establish a 2-gigabit connection using two 1-gigabit NICs trunked together.

Note that Microsoft Windows does not natively support link aggregation (at least up to Win 2003) ^[6]; however some manufacturers provide software for aggregation on their multiport NICs at the device driver layer. Intel, for example, has released a package for Linux called Advanced Networking Services (ANS) to bind Intel Fast Ethernet and Gigabit cards.^[7] Nvidia also supports "teaming" with their Nvidia Network Access Manager/Firewall Tool.

In Linux, FreeBSD, NetBSD, OpenBSD, Mac OS X Server, OpenSolaris, Citrix XenServer, VMware ESX Server, and commercial Unix distributions such as AIX, Ethernet bonding (trunking) is implemented on a higher level, and can hence deal with NICs from different manufacturers or drivers, as long as the NIC is supported by the kernel.

Limitations

Order of frames

A limitation on link aggregation is that it would like to avoid reordering Ethernet frames. That goal is approximated by sending all frames associated with a particular session across the same link^[8]. Depending on the traffic, this may not provide even distribution across the links in the trunk.

Single switch

A limitation of link aggregation is that all physical ports in the link aggregation group must reside on the same logical switch which in most scenarios will leave a single point of failure when the physical switch to which both links are connected goes offline.

However, this can be overcome by using vendor-specific extensions which aggregate multiple physical switches into one logical switch. As of 2009^[update], the IEEE has not yet committed resources to standardize this feature.

Same media

The ports and media used in a trunk should, as a rule of thumb, be all of the same type, such as all copper ports (CAT-5E/CAT-6), all multi-mode fiber ports (SX), or all single-mode fiber ports (LX). However more importantly the speed of each link within a trunk should be the same.

Many of today’s switches are PHY independent meaning that in an SFP slot you could have copper, SX, LX , ZX, XD or CWDM GBICs. Maintaining the same PHY is a good rule of thumb however more important is to maintain the same speed on all links. You could use a SX fiber for one link and a LX (longer, diverse path) for the second link. The speed will still be 1 Gbit/s for both links but one path would have a slightly longer transit time which is of no concern.

However if you use two copper links or one copper and one fiber you must ensure that both links negotiate to the same speed be it 10, 100 or 1,000. If one link negotiates to 1,000 Mbit/s and the other to 100 Mbit/s then all session traffic that is forced to use the 100 Mbit/s link will be very slow or become so congested that it becomes virtually unusable. Worst case would be when the 1,000 Mbit/s link fails and all traffic is then placed on the 100 Mbit/s link.

source :http://wikipedia.org

How to Choose the Best Router Switching Path for Your Network

Introduction

There are a plethora of switching paths available to various Cisco routers and Cisco IOS® releases. Which is the best one for your network, and how do they all work? This white paper is an attempt to explain each of the following switching paths so you can make the best decision about which switching path fits your network.

First, examine the forwarding process itself. There are three steps to forwarding a packet through a router:

1. Determine if the packet's destination is reachable.

2. Determine the next hop toward the destination, and the interface through which that next hop is reachable.

3. Rewrite the Media Access Control (MAC) header on the packet so it will successfully reach its next hop.

Each of these steps is critical for the packet to reach its destination.

Note: Throughout this document, the IP switching path is used as an example; virtually all the information provided here is applicable to equivalent switching paths for other protocols, if they exist.

Process Switching

Process switching is the lowest common denominator in switching paths; it is available on every version of IOS, on every platform, and for every type of traffic being switched. Process switching is defined by two essential concepts:

• The forwarding decision and information used to rewrite the MAC header on the packet are taken from the routing table (from the routing information base, or RIB) and the Address Resolution Protocol (ARP) cache, or from some other table that contains the MAC header information mapped to the IP address of each host that is directly connected to the router.

• The packet is switched by a normal process running within IOS. In other words, the forwarding decision is made by a process scheduled through the IOS scheduler and running as a peer to other processes on the router, such as routing protocols. Processes that normally run on the router are not interrupted to process switch a packet.

The figure below illustrates the process switching path.

Examine this diagram in more detail:

1. The interface processor first detects there is a packet on the network media, and transfers this packet to the input/output memory on the router.

2. The interface processor generates a receive interrupt. During this interrupt, the central processor determines what type of packet this is (assume it is an IP packet), and copies it into processor memory if necessary (this decision is platform dependent). Finally, the processor places the packet on the appropriate process' input queue and the interrupt is released.

3. The next time the scheduler runs, it notes the packet in the input queue of ip_input, and schedules this process to run.

4. When ip_input runs, it consults the RIB to determine the next hop and the output interface, then consults the ARP cache to determine the correct physical layer address for this next hop.

5. ip_input then rewrites the packet's MAC header, and places the packet on the output queue of the correct outbound interface.

6. The packet is copied from the output queue of the outbound interface to the transmit queue of the outbound interface; any outbound quality of service takes place between these two queues.

7. The output interface processor detects the packet on its transmit queue, and transfers the packet onto the network media.

Almost all features that effect packet switching, such as Network Address Translation (NAT) and Policy Routing, make their debut in the process switching path. Once they have been proven, and optimized, these features might, or might not, appear in interrupt context switching.

Interrupt Context Switching

Interrupt context switching is the second of the primary switching methods used by Cisco routers. The primary differences between interrupt context switching and process switching are:

• The process currently running on the processor is interrupted to switch the packet. Packets are switched on demand, rather than switched only when the ip_input process can be scheduled.

• The processor uses some form of route cache to find all the information needed to switch the packet.

This figure illustrates interrupt context switching:

Examine this diagram in more detail:

1. The interface processor first detects there is a packet on the network media, and transfers this packet to the input/output memory on the router.

2. The interface processor generates a receive interrupt. During this interrupt, the central processor determines what type of packet this is (assume it is an IP packet), and then begins to switch the packet.

3. The processor searches the route cache to determine if the packet's destination is reachable, what the output interface should be, what the next hop towards this destination is, and finally, what MAC header the packet should have to successfully reach the next hop. The processor uses this information to rewrite the packet's MAC header.

4. The packet is now copied to either the transmit or output queue of the outbound interface (depending on various factors). The receive interrupt now returns, and the process that was running on the processor before the interrupt occurred continues running.

5. The output interface processor detects the packet on its transmit queue, and transfers the packet onto the network media.

The first question that comes to mind after reading this description is "What is in the cache?" There are three possible answers, depending on the type of interrupt context switching:

• Fast Switching

• Optimum Switching

• Cisco Express Forwarding

Fast Switching

Fast switching stores the forwarding information and MAC header rewrite string using a binary tree for quick lookup and reference. This figure illustrates a binary tree:

In Fast Switching, the reachability information is indicated by the existence of a node on the binary tree for the destination of the packet. The MAC header and outbound interface for each destination are stored as part of the node's information within the tree. The binary tree can actually have 32 levels (the tree above is extremely abbreviated for the purpose of illustration).

In order to search a binary tree, you simply start from the left (with the most significant digit) in the (binary) number you are looking for, and branch right or left in the tree based on that number. For instance, if you are looking for the information related to the number 4 in this tree, you would begin by branching right, because the first binary digit is 1. You would follow the tree down, comparing the next digit in the (binary) number, until you reach the end.

Characteristics of the Fast Switching

Fast Switching has several characteristics that are a result of the binary tree structure and the storage of the MAC header rewrite information as part of the tree nodes.

• Because there is no correlation between the routing table and the fast cache contents (MAC header rewrite, for example), building cache entries involves all the processing that must be done in the process switching path. Therefore, fast cache entries are built as packets are process switched.

• Because there is no correlation between the MAC headers (used for rewrites) in the ARP cache and the structure of the fast cache, when the ARP table changes, some portion of the fast cache must be invalidated (and recreated through the process switching of packets).

• The fast cache can only build entries at one depth (one prefix length) for any particular destination within the routing table.

• There is no way to point from one entry to another within the fast cache (the MAC header and outbound interface information are expected to be within the node), so all routing recursions must be resolved while a fast cache entry is being built. In other words, recursive routes cannot be resolved within the fast cache itself.

Aging Fast Switching Entries

In order to keep the fast switching entries from losing their synchronization with the routing table and ARP cache, and to keep unused entries in the fast cache from unduly consuming memory on the router, 1/20th of the fast cache is invalidated, randomly, every minute. If the routers memory drops below a very low watermark, 1/5th of the fast cache entries are invalidated every minute.

Fast Switching Prefix Length

What prefix length does the fast switching build entries for if it can only build to one prefix length for every destination? Within the terms of the fast switching, a destination is a single reachable destination within the routing table, or a major network. The rules for deciding what prefix length to build a given cache entry are:

• If building a fast policy entry, always cache to /32.

• If building an entry against an Multiprotocol over ATM virtual circuit (MPOA VC), always cache to /32.

• If the network is not subnetted (it is a major network entry):

  • If it is directly connected, use /32;

  • Otherwise use the major net mask.

• If it is a supernet use the supernet's mask.

• If the network is subnetted:

  • If directly connected, use /32;

  • If there are multiple paths to this subnet, use /32;

  • In all other cases, use longest prefix length in this major net.

Load Sharing

Fast switching is entirely destination based; load sharing occurs on a per-destination basis. If there are multiple equal cost paths for a particular destination network, fast cache has one entry for each host reachable within that network, but all traffic destined to a particular host follows one link.

Optimum Switching

Optimum switching stores the forwarding information and the MAC header rewrite information in a 256 way multiway tree (256 way mtree). Using an mtree reduces the number of steps which must be taken when looking up a prefix, as illustrated in the next figure.

Each octet is used to determine which of the 256 branches to take at each level of the tree, which means there are, at most, 4 lookups involved in finding any destination. For shorter prefix lengths, only one-three lookups may be required. The MAC header rewrite and output interface information are stored as part of the tree node, so cache invalidation and aging still occur as in the fast switching.

Optimum Switching also determines the prefix length for each cache entry in the same way as fast switching.

Cisco Express Forwarding

Cisco Express Forwarding, also uses a 256 way data structure to store forwarding and MAC header rewrite information, but it does not use a tree. Cisco Express Forwarding uses a trie, which means the actual information being searched for is not in the data structure; instead, the data is stored in a separate data structure, and the trie simply points to it. In other words, rather than storing the outbound interface and MAC header rewrite within the tree itself, Cisco Express Forwarding stores this information in a separate data structure called the adjacency table.

This separation of the reachability information (in the Cisco Express Forwarding table) and the forwarding information (in the adjacency table), provides a number of benefits:

• The adjacency table can be built separately from the Cisco Express Forwarding table, allowing both to build without process switching any packets.

• The MAC header rewrite used to forward a packet isn't stored in cache entries, so changes in a MAC header rewrite string do not require invalidation of cache entries.

• Recursive routes can be resolved by pointing to the recursed next hop, rather than directly to the forwarding information.

Essentially, all cache aging is eliminated, and the cache is pre-built based on the information contained in the routing table and ARP cache. There is no need to process switch any packet to build a cache entry.

Other Entries in the Adjacency Table

The adjacency table can contain entries other than MAC header rewrite strings and outbound interface information. Some of the various types of entries that can be placed in the adjacency table include:

• cache—A MAC header rewrite string and outbound interface used to reach a particular adjacent host or router.

• receive—Packets destined to this IP address should be received by the router. This includes broadcast addresses and addresses configured on the router itself.

• drop—Packets destined to this IP address should be dropped. This could be used for traffic denied by an access list, or routed to a NULL interface.

• punt—Cisco Express Forwarding cannot switch this packet; pass it to the next best switching method (generally fast switching) for processing.

• glean—The next hop is directly attached, but there are no MAC header rewrite strings currently available.

Glean Adjacencies

A glean adjacency entry indicates that a particular next hop should be directly connected, but there is no MAC header rewrite information available. How do these get built and used? A router running Cisco Express Forwarding and attached to a broadcast network, as shown in the figure below, builds a number of adjacency table entries by default.

The four adjacency table entries built by default are:

10.1.1.0/24, version 17, attached, connected
0 packets, 0 bytes
 via Ethernet2/0, 0 dependencies
   valid glean adjacency
10.1.1.0/32, version 4, receive
10.1.1.1/32, version 3, receive
10.1.1.255/32, version 5, receive

Note there are four entries: three receives, and one glean. Each receive entry represents a broadcast address or an address configured on the router, while the glean entry represents the remainder of the address space on the attached network. If a packet is received for host 10.1.1.50, the router attempts to switch it, and finds it resolved to this glean adjacency. Cisco Express Forwarding then signals that an ARP cache entry is needed for 10.1.1.50, the ARP process sends an ARP packet, and the appropriate adjacency table entry is built from the new ARP cache information. After this step is complete, the adjacency table has an entry for 10.1.1.50.

10.1.1.0/24, version 17, attached, connected
0 packets, 0 bytes
 via Ethernet2/0, 0 dependencies
   valid glean adjacency
10.1.1.0/32, version 4, receive
10.1.1.1/32, version 3, receive
10.1.1.50/32, version 12, cached adjacency 208.0.3.2
0 packets, 0 bytes
 via 208.0.3.2, Ethernet2/0, 1 dependency
   next hop 208.0.3.2, Ethernet2/0
   valid cached adjacency
   10.1.1.255/32, version 5, receive

The next packet the router receives destined for 10.1.1.50 is switched through this new adjacency.

Load Sharing

Cisco Express Forwarding also takes advantage of the separation between the Cisco Express Forwarding table and the adjacency table to provide a better form of load sharing than any other interrupt context switching mode. A loadshare table is inserted between the Cisco Express Forwarding table and the adjacency table, as illustrated in this figure:

The Cisco Express Forwarding table points to this loadshare table, which contains pointers to the various adjacency table entries for available parallel paths. The source and destination addresses are passed through a hash algorithm to determine which loadshare table entry to use for each packet. Per packet load sharing can be configured, in which case each packet uses a different loadshare table entry.

Each loadshare table has 16 entries among which the paths available are divided based on the traffic share counter in the routing table. If the traffic share counters in the routing table are all 1 (as in the case of multiple equal cost paths), each possible next hop receives an equal number of pointers from the loadshare table. If the number of available paths is not evenly divisible into 16 (since there are 16 loadshare table entries), some paths will have more entries than others.

Beginning in Cisco IOS Software Release 12.0, the number of entries in the loadshare table is reduced to make certain each path has a proportionate number of loadshare table entries. For instance, if there are three equal cost paths in the routing table, only 15 loadshare table entries are used.

Which Switching Path Is Best?

Whenever possible, you want your routers to be switching in the interrupt context because it is at least an order of a magnitude faster than process level switching. Cisco Express Forwarding switching is definitely faster and better than any other switching mode. We recommend you use Cisco Express Forwarding if the protocol and IOS you are running supports it. This is particularly true if you have a number of parallel links across which traffic should be load shared. Access the Cisco Feature Navigator (registered customers only) page to determine which IOS you need for CEF support.

source :http://www.cisco.com

Introduction to NetFlow

NetFlow is a technology that lets a router export information about current traffic to a collector for analysis. The analysis might be real time, such as to detect a denial of service attack, or not real time, such as to view trending information.

NetFlow is concerned with flows, which are a one way session between a source and a destination. The router is already caching information about the flow to help with the routing/switching function, NetFlow is an export of this information.

If you SSH to a server, that generates two flows. One is the connection from your ephemeral port to port 22 of the server, and one from port 22 back to your ephemeral port.

The analysis available with NetFlow is more fine-grained than what you get with SNMP. The flow contains the start and end time of the flow, the source and destination IP addresses and ports, the amount of data transferred, and autonomous system (AS) information (if the router is running BGP). There are other things, such as TCP flag information, QoS tags, and optional proprietary information, but the above gives us enough to proceed.

I’ve been playing with NetFlow for a while and have generated various reports. Every time I do something I seem to be starting from scratch, so I’m going to formalize my work on this blog. At the moment I am working on two NetFlow related projects. The first is to figure out the breakdown of protocols over our WAN. The second is to analyze our Internet usage, analyze peering, and detect DDOS traffic patterns in near-real time, or on an ad-hoc basis. I use the flow-tools package for Linux, along with some shell/perl/ruby scripting.

source :http://ccnprecertification.com

Collecting NetFlow data

In the NetFlow world, a NetFlow exporter sends flow data to a NetFlow collector. The exporter is usually a router, the collector is usually a Unix server of some sort.

First, set up your router to export flow information:

ip flow-cache timeout active 2
mls flow ip full
mls flow ipx destination
mls nde sender
mls nde interface
mls nde flow include protocol tcp
ip flow-export source GigabitEthernet1/1
ip flow-export version 5 origin-as
ip flow-export destination X.X.X.X 2055

Where X.X.X.X is the address of your NetFlow collector, and GigabitEthernet1/1 is the router’s interface on that subnet. (This was taken from a 7600 router, you may not need the NDE stuff if you’re on a different platform)

Then, on each interface you want to capture flows for,

ip route-cache flow

You can check on the status of the export with

ROUTER#show ip flow export
Flow export is enabled
 Exporting flows to X.X.X.X (2055)
 Exporting using source interface GigabitEthernet1/1
 Version 5 flow records, origin-as
 235556663 flows exported in 7945727 udp datagrams
 0 flows failed due to lack of export packet
 743 export packets were sent up to process level
 0 export packets were dropped due to no fib
 18425 export packets were dropped due to adjacency issues
 0 export packets were dropped due to fragmentation failures
 0 export packets were dropped due to encapsulation fixup failures
 0 export packets were dropped enqueuing for the RP
 0 export packets were dropped due to IPC rate limiting

You can immediately see some statistics now that you have NetFlow enabled:

#show ip cache flow
IP packet size distribution (4086M total packets):
  1-32   64   96  128  160  192  224  256  288  320  352  384  416  448  480
  .001 .627 .032 .012 .020 .019 .085 .009 .001 .002 .003 .005 .006 .006 .006
   512  544  576 1024 1536 2048 2560 3072 3584 4096 4608
  .005 .004 .005 .066 .079 .000 .000 .000 .000 .000 .000
IP Flow Switching Cache, 4456704 bytes
 417 active, 65119 inactive, 235561367 added
 132171494 ager polls, 0 flow alloc failures
 Active flows timeout in 2 minutes
 Inactive flows timeout in 15 seconds
 last clearing of statistics never
Protocol         Total    Flows   Packets Bytes  Packets Active(Sec) Idle(Sec)
--------         Flows     /Sec     /Flow  /Pkt     /Sec     /Flow     /Flow
TCP-Telnet       12352      0.0        24    44      0.0       3.9      13.3
TCP-FTP          50507      0.0         1    55      0.0       0.7      14.4
TCP-FTPD         18867      0.0         1   499      0.0       0.5      15.0
TCP-WWW      158177053     36.8        17   186    627.8       3.3       8.9
TCP-SMTP        139330      0.0         1   135      0.0       0.0      15.4
TCP-X               23      0.0         2   222      0.0       1.8       9.4
TCP-BGP              2      0.0         1    64      0.0       0.0      15.7
TCP-NNTP             3      0.0         1    56      0.0       0.0      11.0
TCP-other     17276962      4.0        21   318     85.9       3.1       8.8
UDP-DNS        2866156      0.6         1    68      0.8       0.5      15.4
UDP-NTP        2082119      0.4         1    84      0.4       0.0      15.4
UDP-TFTP           137      0.0         5    49      0.0      20.4      15.5
UDP-Frag          3796      0.0     26195  1394     23.1      20.5      14.7
UDP-other     48352973     11.2        15   275    173.6      10.8      14.8
ICMP           3302490      0.7         6   165      5.0       6.5      14.8
GRE            1844456      0.4        38   137     16.7     116.5       1.1
IP-other       1433724      0.3        53    52     17.8     111.4       2.5
Total:       235560950     54.8        17   240    951.5       6.4      10.3

To collect the flows, install the flow-tools package, with either

yum install flow-tools

or whatever your distribution uses (apt-get install flow-tools), or install from source.

The flow-capture utility is the one that is used to write the flows to disk. It must be configured with the port (2055 in our case), and a location to write the flows to. In CentOS/RedHat/Fedora, this is done in /etc/sysconfig/flow-capture.

OPTIONS="-n 287 -N 0 -w /var/flow-tools -S 5 0/0/2055"

• -n 287: 287 files per day, or one file every 5 minutes. I recommend doing this instead of the default 15 minutes so that you have more real time access to your data, and some tools depend on this reporting interval.
• -N 0: Don’t nest the files. All the flow files will be in one directory instead of one per day.
• -w /var/flow-tools: Write to this directory
• -S 5: Syslog a message every 5 minutes with the collection statistics
• 0/0/2055: listen on all interfaces to all exporters on port 2055

You may also want to configure something like tmpwatch in cron to clean up files (/usr/sbin/tmpwatch 720 /var/flow-tools) to only keep the last month or whatever you want. On a pipe that’s used 100-200MB/sec, you can expect at least 10G of data to be logged.

Start flow-capture (service flow-capture start), and look for files in /var/flow-tools.

The files are binary, so you can’t look at them directly. To have a look at what’s there:

# flow-cat /var/flow-tools/ft-v05.2008-12-22.080500-0600 | flow-print | head
srcIP            dstIP            prot  srcPort  dstPort  octets      packets
x.x.x.105      x.x.x.151        6     4511     80       744         6
x.x.x.105      x.x.x.151        6     4512     80       985         12
x.x.x.105      x.x.x.151        6     4514     80       784         7
x.x.x.105      x.x.x.185        6     4516     80       985         6
x.x.x.105      x.x.x.52         6     4517     80       1744        7
x.x.x.105      x.x.x.41         6     4518     80       850         5
x.x.x.115      x.x.x.255       17    138      138      229          1
x.x.x.252      x.x.x.62         6     2727     80       40          1
x.x.x.105      x.x.x.27         6     4521     80       2221        22

The fields should be fairly self explanatory. The -f parameter to flow-print allows you to print out new data.

Source :http://ccnprecertification.com

CCNA - Network Academy (Cisco Certified Network Associate (CCNA))

The CCNA (Cisco Certified Network Associate) Course consists of 4 Semesters, each focussing on a different area of networking.

The curriculum is an online learning program, each split into chapters with an exam at the end of each to check your progress. Once you have completed all of the chapters, which have online exams which have an average of about 25 questions each, which are multiple choice, with four answers to choose from. Once completed you see your percentage so you know whether you have passed instantly, you sit another online end of semester exam, The exams are easily passable if you put the effort in.

Semester 1

Semester 1 Introduces the course and starts of by explaining networking basics and introduces things like the OSI layered network design model, explaining each layer of it in some detail.


Semester 2

This Semester focuses mainly on Routers and their components, protocols, configurations and commands etc. And reinforces what you have learned about IP addressing and WANS from Semester 1

Semester 3

Switches are the main topic in this semester, teaching you about LAN switching in a lot greater depth than covered in the previous chapters. Also LAN design, Access control lists and other protocols are covered thoroughly.

Semester 4

Semester 4 covers WAN's mainly, which includes WAN design, point to point, frame-relay and ISDN networks and general network management. Then goes on to give you review chapters of the CCNA to help you revise before the final exam.

As well as all the online learning, there is practical experience available via labs, which are integrated into the curriculum letting you see how things actually work, not just the theory behind them, this also helps you remember commands for the routers and is good practice for the future.

All the way through the course you can keep track of your progress on the academy website which gives
you access to all of the exam results you have achieved to date. Once you have completed a Semester and have passed the final exam you receive a certificate to show you have passed which contains your result.

The final exam costs around £90 (I hope) if I remember correctly but if done at a college or 6th from they either pay some towards it or pay it all for you, I'm not too sure, but it isn't too expensive as it is a widely accepted qualification into the networking industry, and looks good on a C.V. The qualification only lasts about three years once received.

source :http://www.dooyoo.co.uk/