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When you’re getting started on your CCNA studies on your way to earning this certification, you’re swamped with network device types that you’re familiar with, but not quite sure how to use. Let’s look at these networking devices and their main purposes.

Hubs and repeaters operate at Layer One of the OSI model, and they have one main purpose – regenerating the electrical signal that Layer One technologies carry. This regeneration helps to avoid attenuation, the gradual weakening of a signal. Much like a radio signal, the electric signals that travel at Layer One gradually weaken as they travel across the wire. Hubs and repeaters both generate a “clean” copy of the signal.

While hubs and repeaters can be helpful, they do nothing as far as network segmentation is concerned. The first such device we encounter as we move up the OSI model is the switch. Operating at Layer 2, a switch creates multiple collision domains by default each switch port is considered its own little collision domain. If 12 PCs are connected to a Cisco switch, you have 12 separate collision domains.

Switches can be used to segment the network into smaller broadcast domains, but this is not a default behavior. Virtual LAN (VLAN) configuration segments the network into smaller broadcast domains, since a broadcast sent by a host in one VLAN is heard only by other devices in the same VLAN.

Routers operate at Layer 3 of the OSI model and segment a network into multiple broadcast domains by default. Routers do not forward broadcasts as switches do, making the router the only device of the four we’ve discussed today that create multiple broadcast domains by default.

Knowing what each of these devices can and cannot do is essential to passing the CCNA and becoming a great network administrator. Good luck to you in both of these goals!

When you’re studying to pass the CCNA exam and earn your certification, you’re introduced to a great many terms that are either totally new to you or seem familiar, but you’re not quite sure what they are. The term “collision domain” falls into the latter category for many CCNA candidates.

What exactly is “colliding” in the first place, and why do we care? It’s the data that is being sent out onto an Ethernet segment that we’re concerned with here. Ethernet uses Carrier Sense Multiple Access / Collision Detection (CSMA/CD) to avoid collisions in the first place. CSMA/CD is a set of rules dictating when hosts on an Ethernet segment can and cannot transmit data. Basically, a host that wants to transmit data will “listen” to the ethernet segment to see if another host is currently transmitting. If no one else is transmitting, the host will go forward with its own transmission.

This is an effective way of avoiding a collision, but it is not foolproof. If two hosts follow this procedure at the exact same time, their transmissions will collide on the Ethernet segment and both transmissions will become unusable. The hosts that sent those two transmissions will then send a jam signal out onto the segment, indicating to all other hosts that they should not send data. The two hosts will each start a random timer, and at the end of that time each host will begin the listening process again.

Now that we know what a collision is, and what CSMA/CD is, we need to be able to define a collision domain. A collision domain is any area where a collision can theoretically take place, so only one device can transmit at a time in a collision domain.

In another free CCNA certification tutorial, we saw that broadcast domains were defined by routers (default) and switches if VLANs have been defined. Hubs and repeaters did nothing to define broadcast domains. Well, they don’t do anything here, either. Hubs and repeaters do not define collision domains.

Switches do, however. A Cisco switchport is actually its own unshared collision domain! Therefore, if we have 20 host devices connected to separate switchports, we have 20 collision domains. All 20 devices can transmit simultaneously with no danger of collisions. Compare this to hubs and repeaters – if you have five devices connected to a single hub, you still have one large collision domain, and only one device at a time can transmit.

Mastering the definition and creation of collision domains and broadcast domains is an important step toward earning your CCNA and becoming an effective network administrator. Best of luck to you in both these worthwhile pursuits!

When you’re studying to pass the CCNA exam and earn your certification, you’re introduced to a great many terms that are either totally new to you or seem familiar, but you’re not quite sure what they are. The term “broadcast domain” falls into the latter category for many CCNA candidates.

A broadcast domain is simply the group of end hosts that will receive a broadcast sent out by a given host. For example, if there are ten host devices connected to a switch and one of them sends a broadcast, the other nine devices will receive the broadcast. All of those devices are in the same broadcast domain.

Of course, we probably don’t want every device in a network receiving every single broadcast sent out by any other device in the network! This is why we need to know what devices can create multiple, smaller broadcast domains. Doing so allows us to limit the broadcasts traveling around our network – and you might be surprised how much traffic on some networks consists of unnecessary broadcasts.

Using the OSI model, we find devices such as hubs and repeaters at Layer One. This is the Physical layer, and devices at this layer have no effect on broadcast domains.

At Layer Two, we’ve got switches and bridges. By default, a switch has no effect on broadcast domains; CCNA candidates know that a switch will forward a broadcast out every single port on that switch except the one upon which it was received. However, Cisco switches allow the creation of Virtual Local Area Networks, or VLANs, that are logical segments of the network. A broadcast sent by one host in a VLAN will not be forwarded out every other port on the switch. That broadcast will be forwarded only out ports that are members of the same VLAN as the host device that sent it.

The good news is that broadcast traffic will not be forwarded between VLANs. The bad news is that no inter-VLAN traffic at all is allowed by default! You may actually want this in some cases, but generally you’re going to want inter-VLAN traffic. This requires the use of a router or other Layer 3 device such as a Layer 3 Switch. (Layer 3 Switches are becoming more popular every day. Basically, it’s a switch that can also run routing protocols. These switches are not tested on the CCNA exam.)

That router we just talked about also defines broadcast domains. Routers do not forward broadcasts, so broadcast domains are defined by routers with no additional configuration.

Knowing how broadcasts travel across your network, and how they can be controlled, is an important part of being a CCNA and of being a superior network administrator. Best of luck to you in both of these pursuits!

Once you earn your CCNA certification, you’ve got quite a few exciting choices ahead of you! The majority of CCNAs go on to pursue another Cisco certification, and this is a wise decision. The more you know, the more valuable you are in today’s IT market.

A question I’m often asked by new CCNAs is “Which certification should I go after next?” Often, these new CCNAs have their eye on the Cisco Certified Security Professional (CCSP) certification. While adding a security certification to your resume is an excellent idea, I strongly recommend that new CCNAs acquire their Cisco Certified Network Professional (CCNP) certification before pursuing their security certifications. The CCNP requires you to pass three or four exams (depending on the path you choose) that will demand a further mastery of some subjects you studies to earn your CCNA as well as several important topics that you haven’t seen yet.

The CCNP builds on the foundation of networking knowledge you built when you earned your CCNA, and your CCNP study will add greatly to your skills and resume. There are some common technologies that you’ll see in many networks – BGP and route redistribution among them – that you don’t learn about in your CCNA studies. By pursuing your CCNP, you’ll also learn much more about OSPF, switching, and refine your troubleshooting skills. These are skills that will pay off in your current job as well as any future job hunting you do.

To earn your CCNP, you’ve got to pass some very rigorous Cisco exams, and you also need to know the rules regarding this important certification. In this article, I’ll answer some of the most commonly asked questions regarding the CCNP.

Q: What exams do I need to pass to get my CCNP?

A: You have two options, a three-exam path and a four-exam path. Currently, the four-exam path consists of rigorous exams on advanced routing techniques (BSCI), advanced switching (BCMSN), remote access methods (BCRAN), and advanced troubleshooting techniques (CIT). The three-exam path combines the BCMSN and BSCI exams into a single exam, the Composite exam.

Q: Do I have to take them in any order?

A: No, the order is up to the candidate. Most CCNP candidates take the BSCI exam first and the CIT exam last, but again this is up to the candidate.

Q: What else do I have to do to get the CCNP?

A: You must earn your CCNA before you can be CCNP certified (as well as passing the exams, of course).

Q: Is there a recertification requirement?

A: Cisco CCNP certifications are valid for three years. During that time, you must either pass the Composite exam, the BSCI and BCMSN exams, or pass any CCIE written exam.

Q: What if I don’t recertify within the three-year period?

A: You must then meet whatever CCNP requirements there are at that time, from the beginning. It’s easier to make sure you recertify!

Becoming CCNP certified is a great boost to your career and your confidence, and as with any Cisco certification, it’s up to you to stay current with the CCNA and CCNP requirements. Visit the Career Certification section of Cisco’s website regularly to learn about the program’s requirements and changes.

Whether you’re thinking of starting a career with computers and information technology, or thinking about earning a professional certification such as the CCNA or MCSE to accelerate your career, there is no better time to start than today. Silicon Valley is hiring again, and while we all can’t work for Google, IT hiring is at its highest level in years and the opportunities for driven, motivated individuals are unlimited.

I also know that for many of us, the holiday season is a good excuse to put off those studies! “I’ll study for the CCNA after Thanksgiving…” “I’ll start working on my CCNP after the New Year…” Well, guess what – the new year is here.

It’s 2006. Where is your IT career? Are you actively studying to earn a certification, or are you still thinking about it? Are you attending a school to break into the IT field, or are you still thinking about it?

Newton’s First Law Of Motion states that an object at rest tends to stay at rest, and an object at motion tends to stay in motion. This is true of careers as well, including yours. Where do you want your career to be in one year? Do you want to have earned several certifications in that time, therefore advancing your career, or do you want to be in the exact same place you are today?

The only person who can make this decision is you. And I can speak from experience that when you begin putting your career into motion – the possibilities are unlimited. But you have to get started – today!

When you’re studying to pass the BSCI exam and earn your CCNP certification, you’re going to be introduced to ISIS. ISIS and OSPF are both link-state protocols, but ISIS works quite differently from OSPF. You must master these details in order to earn your CCNP.

One of the major differences between OSPF and ISIS will be evident to you when you first begin your BSCI exam studies, and that is the terminology. ISIS uses terms that no other protocol you’ve studied to date uses, and learning these new terms is the first step to BSCI and CCNP exam success.

First off, what does “IS” stand for in “ISIS”? It stands for “Intermediate System”, which sounds like a group of routers. As opposed to Autonomous Systems, which are logical groups of routers, an Intermediate System is simply a single router. That’s it.

You’ll also become familiar with End Systems, referred to in ISIS as an “ES”. The End System is simply an end host.

ISIS and OSPF both use the concept of areas, but ISIS takes a different approach to this concept. ISIS routers use three different types of routing levels, according to the area a router has been placed in. Level 2 routers are connected only to the backbone and serve as a transit device between non-backbone areas. Level 1 routers are totally internal to a non-backbone area.

ISIS uses both Level-1 and Level-2 Hellos, meaning that the two types of routers just mentioned cannot form an adjacency. Luckily for us, there is a middle ground, and that is the Level 1-2 router. These routers connect non-backbone areas to backbone areas. L1-L2 routers keep two separate routing tables, one for L1 routing and another for L2 routing. This is the default setting for a Cisco router, and L1-L2 routers can form adjacencies with both L1 and L2 routers.

Part of the challenge of learning ISIS is getting used to the differences between ISIS and OSPF. Keep studying the terminology, master one concept at a time, and soon you’ll be a master of ISIS and a CCNP to boot!

One question I see often on the ‘Net is “Is it worth my time to earn a CCNA / CCNP / CCIE certification?” My personal answer to that is a resounding yes. The power of Cisco certifications has allowed me to create a tremendous career, and they can do the same for you.

There has never been a better time to accelerate your IT career, and earning a technical certification is a great way to do just that. I don’t care if you’re looking at earning an MCSE, a Cisco certification, Red Hat, or any other vendor – you are always better off having a technical certification than not having one. Technical certifications are an excellent way to market yourself and stand out from the crowd. Earning certifications shows a potential employer (and your current one) that you are willing to go the extra mile.

Sadly, when you ask this question on most Internet message boards, you’re going to get some very negative people giving you their “unbiased” opinion. Ask yourself this question: Do you want to entrust the direction of your career to someone you don’t know, has no accountability for what they say, and has some kind of ax to grind? Do you want someone like that to decide whether you should earn a CCNA or CCNP?

I can speak from experience on this point. When I told a few people that I was going to earn my CCIE, almost 100% of the responses I got were negative. “It’s too hard”, “no one can pass that”, “the CCIE isn’t worth the work”, etc. Every single one of these statements is false, and again I speak from firsthand experience. The same is true for the CCNA, CCNP, and MCSE. All of these certifications can add value to your career and put more money in your pocket. But you have to make the decision to earn them and to “keep your goals away from the trolls”.

Don’t ask anonymous strangers whether it’s “worth the time” to get a CCNA, MCSE, or other computer certification. The only person you should ask that question of is yourself. Whether you want to start an IT career or jumpstart your current one, make the decision to move forward in your career – and then follow through on that decision.

When you’re preparing to pass the BSCI exam and earn your CCNP certification, one of the biggest challenges is learning BGP. BGP is totally different from any protocol you learned to earn your CCNA certification, and one of the differences is that BGP uses path attributes to favor one path over another when multiple paths to or from a destination exist.

Notice I said “to or from”. In earlier free BGP tutorials, I discussed the BGP attributes “weight” and “local preference”. These attributes are used to favor one path to a destination over another; for example, if BGP AS 100 has two paths to a destination in AS 200, these two attributes can be set in AS 100 to favor one path over another. But what if AS 100 wants to inform the routers in AS 200 as to which path it should use to reach a given destination in AS 100?

That’s where the BGP attribute “Multi-Exit Discriminator”, or MED, comes in. The MED value can be set in AS 100 to tell AS 200 which path it should use to reach a given network in AS 100.

As with many BGP attributes, the MED can be set with a route-map. What you need to watch is that there is no “set med” value in route maps. To change the MED of a path, you need to change the metric of that path. Let’s say that there are two entry paths for AS 200 to use to reach destinations in AS 100. You want AS 200 to use the 100.1.1.0/24 path over the 100.2.2.0/24 path. First, identify the two paths with two separate ACLs.

R1(config)#access-list 22 permit 100.1.1.0 0.0.0.255

R1(config)#access-list 23 permit 100.2.2.0 0.0.0.255

Next, write a route-map that assigns a lower metric to the more-desirable path.

R1(config)#route-map PREFER_PATH permit 10

R1(config-route-map)#match ip address 22

R1(config-route-map)#set metric 100

R1(config-route-map)#route-map PREFER_PATH permit 20

R1(config-route-map)#match ip address 23

R1(config-route-map)#set metric 250

Finally, apply the route-map to the neighbor or neighbors.

R1(config-route-map)#router bgp 100

R1(config-router)#neighbor 22.2.2.2 route-map PREFER_PATH out

The key points to keep in mind is that while many BGP attributes prefer a higher value, the MED is basically an external metric – and a lower metric is preferred, just as with the protocols you’ve already studied to earn your CCNA certification.

To pass the CCNA exam and earn that coveted certification, you’ve got to know Cisco switches inside and out. Among the many important details you’ve got to know are the three methods that Cisco switches use to forward frames, and the differences between the three.

The first switching method is Store-and-Forward. The name is the recipe, because that’s just what the switch does – it stores the entire frame before beginning to forward it. This method allows for the greatest amount of error checking, since the Frame Check Sequence (FCS) can be run before the frame is forwarded. As always, there is a tradeoff, since this error checking process makes this the slowest of the three frame forwarding methods.

The quickest method is Cut-Through, where only the destination MAC address of the frame is examined before the forwarding process begins. This means that the part of the frame is actually being forwarded as it is still being received! The tradeoff here is that the FCS does not run, so there is absolutely no error checking with Cut-Through switching.

The middle ground between these two extremes is Fragment-Free, so named since fragmented frames will not be forwarded. The switch examines only the first 64 bytes of the frame for errors, since that is the part of the frame that will be damaged in case of a collision. There is error checking, but it is not as thorough as Store-and-Forward.

Keeping these three switching schemes straight is vital to your CCNA exam efforts, and it will help you in working with Cisco switches in the real world as well. Keep studying!