Cisco Solution: August 2007

Cisco CCNA/CCNP Home Lab Setup: How To Configure Reverse Telnet

Occasionally, during your CCNA and CCNP studies, you'll run into a term that just doesn't quite make sense to you. (Okay, more than occasionally!) One such term is "reverse telnet". As a Cisco certification candidate, you know that telnet is simply a protocol that allows you to remotely connect to a networking device such as a router or switch. But what is "reverse telnet", and why is it so important to a Cisco CCNA / CCNP home lab setup?

Where a telnet session is started by a remote user who wants to remotely control a router or switch, a reverse telnet session is started when the host device itself imitates the telnet session.

In a CCNA / CCNP home lab, reverse telnet is configured and used on the access server. The access server isn't a white box server like most of us are used to; an access server is a Cisco router that allows you to connect to multiple routers and switches with one session without having to move a rollover cable from device to device.

Your access server will use an octal cable to connect to the other routers and switches in your home lab. The octal cable has one large serial connector that will connect to the access server, and eight rj-45 connectors that will connect to your other home lab devices. Your access server then needs an IP Host table in order to perform reverse telnet.

An IP Host table is easy to put together (and you better know how to write one to pass the CCNA!). The IP Host table is used for local name resolution, taking the place of a DNS server. A typical access server IP Host table looks like this:

ip host FRS 2007 100.1.1.1

ip host R3 2003 100.1.1.1

ip host R1 2001 100.1.1.1

ip host R2 2002 100.1.1.1

ip host R4 2004 100.1.1.1

ip host R5 2005 100.1.1.1

ip host SW1 2006 100.1.1.1

interface Loopback0

ip address 100.1.1.1 255.255.255.255

no ip directed-broadcast

This configuration will allow you to use your access server to connect to five routers, a frame relay switch, and a switch without ever moving a cable. When you type "R1" at the console line, for example, you'll be connected to R1 via reverse telnet. If you have a smaller lab, an access server is still a real timesaver and an excellent investment. And by getting a static IP address to put on your access server, you can even connect to your home lab from remote locations!

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage (http://www.thebryantadvantage.com ), home of free CCNA and CCNP tutorials, and The Ultimate CCNA and CCNP Study Packages. For a copy of his FREE "How To Pass The CCNA" or "CCNP" ebook, visit the website and download your copies!

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Cisco CCNP Certification: BGP Attribute Category Tutorial

You have to master the details on BGP to pass the BSCI exam and to earn your CCNP, but BGP is an entirely new world from the protocols you studied to earn your CCNA. BGP paths contain attributes, while no protocol you studied for the CCNA carried. BGP Attributes are used to choose the best path when multiple loop-free paths exist, as well as give you other specific information about the paths. This additional information includes the autonomous systems that are along the path to a given destination, what the next-hop IP address is, and much more.

Before we examine the specific attributes, we need to understand the categories used to differentiate BGP attributes. Some attributes are required, some aren't; some attributes will be carried between routers, where others will not.

The first category is the well-known mandatory attribute. As you'd expect, these attributes are required and will be understood by all BGP speakers. Mandatory attributes include the origin code, AS_Path, and next-hop.

Well-known discretionary attributes don't have to be present, but if they are , all BGP speakers will understand their meaning. BGP attributes that fall into this category are the MED, local preference, and atomic aggregate.

Optional transitive attributes may not be fully understood by all BGP speakers, but the attributes are sent between routers as paths are exchanged. The aggregator and community attributes fall into this category.

Finally, we have the optional nontransitive attribute. If a BGP speaker does not understand this attribute, the speaker will not forward the attribute. The Originator ID and Cluster ID are optional nontransitive attributes.

There's one important BGP attribute that was left out of this list; indeed, if you're working in an all-Cisco environment, it may be the most important attribute of all. The weight attribute is Cisco-proprietary, so if you're working in a multivendor environment, this attribute is of limited value. However, the weight attribute is the first attribute considered when BGP is deciding between valid, loop-free paths, so it's an attribute we have to keep in mind. The weight attribute doesn't really fit in any of the four BGP classes we talked about earlier in the article.

If you don't know what these attributes do yet, that's okay. We'll examine each of these attributes in more detail in the next part of this free BGP tutorial. Keep studying!

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage (http://www.thebryantadvantage.com ), home of free CCNA and CCNP tutorials, and The Ultimate CCNA and CCNP Study Packages. For a copy of his FREE "How To Pass The CCNA" or "CCNP" ebook, visit the website and download your copies!

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Cisco Certification: The Cisco Three-Layered Hierarchical Model

Cisco Certification: The Cisco Three-Layered Hierarchical Model

by: www.SemSim.com

Cisco has defined a hierarchical model known as the hierarchical internetworking model. This model simplifies the task of building a reliable, scalable, and less expensive hierarchical internetwork because rather than focusing on packet construction, it focuses on the three functional areas, or layers, of your network:

Core layer: This layer is considered the backbone of the network and includes the high-end switches and high-speed cables such as fiber cables. This layer of the network does not route traffic at the LAN. In addition, no packet manipulation is done by devices in this layer. Rather, this layer is concerned with speed and ensures reliable delivery of packets.

Distribution layer: This layer includes LAN-based routers and layer 3 switches. This layer ensures that packets are properly routed between subnets and VLANs in your enterprise. This layer is also called the Workgroup layer.

Access layer: This layer includes hubs and switches. This layer is also called the desktop layer because it focuses on connecting client nodes, such as workstations to the network. This layer ensures that packets are delivered to end user computers.

Figure INT.2.1 displays the three layers of the Cisco hierarchical model.

When you implement these layers, each layer might comprise more than two devices or a single device might function across multiple layers.The benefits of the Cisco hierarchical model include:

High Performance: You can design high performance networks, where only certain layers are susceptible to congestion.

Efficient management & troubleshooting: Allows you to efficiently organize network management and isolate causes of network trouble.

Policy creation: You can easily create policies and specify filters and rules.

Scalability: You can grow the network easily by dividing your network into functional areas.

Behavior prediction: When planning or managing a network, the model allows you determine what will happen to the network when new stresses are placed on it.

Core Layer

The core layer is responsible for fast and reliable transportation of data across a network. The core layer is often known as the backbone or foundation network because all other layers rely upon it. Its purpose is to reduce the latency time in the delivery of packets. The factors to be considered while designing devices to be used in the core layer are:

High data transfer rate: Speed is important at the core layer. One way that core networks enable high data transfer rates is through load sharing, where traffic can travel through multiple network connections.

Low latency period: The core layer typically uses high-speed low latency circuits which only forward packets and do not enforcing policy.

High reliability: Multiple data paths ensure high network fault tolerance; if one path experiences a problem, then the device can quickly discover a new route.

At the core layer, efficiency is the key term. Fewer and faster systems create a more efficient backbone. There are various equipments available for the core layer. Examples of core layer Cisco equipment include:

Cisco switches such as 7000, 7200, 7500, and 12000 (for WAN use)

Catalyst switches such as 6000, 5000, and 4000 (for LAN use)

T-1 and E-1 lines, Frame relay connections, ATM networks, Switched Multimegabit Data Service (SMDS)

Distribution Layer

The distribution layer is responsible for routing. It also provides policy-based network connectivity, including:

Packet filtering (firewalling): Processes packets and regulates the transmission of packets based on its source and destination information to create network borders.

QoS: The router or layer 3 switches can read packets and prioritize delivery, based on policies you set.

Access Layer Aggregation Point: The layer serves the aggregation point for the desktop layer switches.

Control Broadcast and Multicast: The layer serves as the boundary for broadcast and multicast domains.

Application Gateways: The layer allows you to create protocol gateways to and from different network architectures.

The distribution layer also performs queuing and provides packet manipulation of the network traffic.

It is at this layer where you begin to exert control over network transmissions, including what comes in and what goes out of the network. You will also limit and create broadcast domains, create virtual LANs, if necessary, and conduct various management tasks, including obtaining route summaries. In a route summary, you consolidate traffic from many subnets into a core network connection. In Cisco routers, the command to obtain a routing summary is:

show ip route summary

You can practice viewing routing information using a free CCNA exam router simulator available from SemSim.com. You can also determine how routers update each other's routing tables by choosing specific routing protocols.

Examples of Cisco-specific distribution layer equipment include 2600,4000, 4500 series routers

Access Layer

The access layer contains devices that allow workgroups and users to use the services provided by the distribution and core layers. In the access layer, you have the ability to expand or contract collision domains using a repeater, hub, or standard switch. In regards to the access layer, a switch is not a high-powered device, such as those found at the core layer.

Rather, a switch is an advanced version of a hub.

A collision domain describes a portion of an Ethernet network at layer 1 of the OSI model where any communication sent by a node can be sensed by any other node on the network. This is different from a broadcast domain which describes any part of a network at layer 2 or 3 of the OSI model where a node can broadcast to any node on the network.

At the access layer, you can:

Enable MAC address filtering: It is possible to program a switch to allow only certain systems to access the connected LANs.

Create separate collision domains: A switch can create separate collision domains for each connected node to improve performance.

Share bandwidth: You can allow the same network connection to handle all data.

Handle switch bandwidth: You can move data from one network to another to perform load balancing

SemSim.com provides training resources for Cisco certification exams: CCIE, CCNP, CCNA, CCDP, CCDA. It offers FREE learning resources to students such as study guides and router simulation labs. For more information visit: http://www.SemSim.com : Making Cisco cetification easy!
support@semsim.co

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Cisco Certification: How To Build Your Own Home Lab

CCNA and CCNP candidates hear it all the time: Get some hands-on experience. From my personal experience climbing the Cisco certification ladder, I can tell you firsthand that there is no learning like hands-on learning. No simulator in the world is going to give you the experience you will get cabling and configuring your own routers.

Whenever I mention this to one of my students, they always say it costs too much. The truth is, it is cheaper now to build your own CCNA and CCNP lab than it has ever been. The secret? Used routers.

The word used turns off a lot of people not many of us buy used computers or used servers. Cisco routers, though, are robust. I personally own a Cisco 4000 router that I use as a Frame Relay switch in my lab that Ive had for about four years, and Ive never had a problem with it.

The good news for current CCNA and CCNP candidates interested in building their own labs is that used Cisco equipment has never been more plentiful or cheaper. eBay is a good way to get an idea of whats out there and what the prices are, but you dont have to assemble your lab one piece at a time. Many eBay vendors who sell used Cisco equipment sell ready-made CCNA and CCNP labs for one price, including cables.

I asked one major vendor of CCNA and CCNP labs, www.ciscokits.com, what the most common questions are regarding building your own home lab. Heres what they had to say:

Why do I need real routers instead of a simulator?

You need a physical router,as the simulators just dont have the ability to give you the hands on you need to see what happens when you disconnect a cable or put a cable in the wrong location. You will come to find quickly that mistakes you make on Router 1 are affecting Router 5 all because you did not screw in a cable properly. No simulator can simulate that.

How many routers do I need?

Two routers really are required to see if anything works. If you have a very limited budget, you can receive value from only purchasing a single router over working with a simulator. However, you will not be able to see the main thing we are trying to accomplish. The propagation of route tables!

The only way you can see if your configurations work, is to have at least two routers. Therefore, I strongly recommend that you purchase a dual router kit that comes with all the accessories you need. Otherwise you can spend days trying to find all the little extra pieces you need to get your lab up and running.

Do I need a switch?

Well, it is nice to have. However, with only about 2 questions on the test dedicated to hands on switch knowledge, if you have to skimp on something, skimp on the switch.

What routers and switches should I buy?

Choices, choices, choices! Which 2500/2600 router do I pick? I will list some pros and cons of each router below, along with current prices (note that prices are generally lower if you buy a dual router kit instead of a single router). Please note that prices are approximations.

1) Cisco 2501 Router with 16 MB Flash/16MB DRAM $94.99. The cheapest introduction router, and it can support a vast majority of the commands that you will need to learn for your CCNA test. All 2500 routers that we will discuss come with a minimum of two serial ports and an Ethernet port.

You will need to add a transceiver to this unit to convert the Ethernet AUI port to an RJ-45 style Ethernet port.

2) Cisco 2503 Router with 16 MB Flash/16MB DRAM $119.99. This is the same as a Cisco 2501, except it adds an ISDN port so you can complete all your ISDN commands for the CCNA test. You will need to add a transceiver to convert the Ethernet AUI port to an RJ-45 style Ethernet port.

3) Cisco 2505/2507 with 16 MB Flash/16MB DRAM $109.99. The same as a Cisco 2501 except it has a built-in 8 or 16 port hub so you do not have to purchase a transceiver.

4) Cisco 2514 Router with 16 MB Flash/16MB DRAM $149.99. This router is the same as a Cisco 2501 except instead of one Ethernet port you have two. You may ask, what is the big deal? Well, you can use this as your Cable Modem/DSL Modem router. Now you can test your ability to setup a firewall and router in a live environment on the Internet. Lots of fun! You will need to add two transceivers to convert the Ethernet AUI ports to an RJ-45 style Ethernet ports.

5) Cisco 2520 Router with 16 MB Flash/16MB DRAM $119.99. This is the same as a 2503 but it also adds two more serial ports so you can use this as a frame relay switch later in your CCNA studies. It costs the same as a 2503, so this is a great money saving tip.

6) Cisco 2612 Router with 32 DRAM and 8 MB Flash $199.99. This is a modular router unlike any of the 2500 series routers. So the big benefit of this is you can buy extra modules to add functionality such as more serial ports, ISDN ports, Ethernet ports, WICs and such. However, due to the flexibility you will pay a bit more. One day it is a frame relay switch, the next it is your ISDN router. In the long run it will be cheaper than purchasing a bunch of dedicated routers for each

discipline you want to learn.

7) Cisco 1912 or 1924 Switch with Enterprise Software $109.99. This is a good low cost switch. The only drawback is it is a 10 MB switch except for the two 100 MB uplink ports. Not a big deal since you have 10 MB routers.

8) Cisco 2912 or 2924 Switch with Enterprise Software $249.99. This switch will run all the current commands needed for the test and is a full 100 MB switch.

And should you desire to sell your lab after you complete your certification, you can either negotiate a price with the vendor who sold it to you, or you can sell it yourself on ebay. Its my experience that 95% of candidates who earn their CCNA go on to pursue their CCNP within one year, though, so dont sell it too quickly.

In the end, you spend only a few hundred dollars, and you gain invaluable experience and knowledge that will help you both in your certification quest and your job performance. Having worked my way from the CCNA to the CCIE, I can tell you that you will learn much more from actually configuring and cabling your own equipment than you ever will from any simulation of the real thing.

To your success,

Chris Bryant
CCIE #12933

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage. The Bryant Advantage's website offers FREE ebooks and tutorials for the CCNA and CCNP exams, FREE subscriptions to "Cisco Certification Central", and sells the best CCNA and CCNP prep courses and books on the market today. Visit his site at www.thebryantadvantage.com today!

chris@thebryantadvantage.com

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Cisco CCNA Certification: Why You MUST Have Hands-On Experience

CCNA and CCNP candidates hear it all the time: you have to get some hands-on experience to pass the exams.

Candidates tend to think thats just so they can solve the simulator problems, but thats only the more obvious reason.

First, I want to make it clear that Im not bashing learning from books you have to learn theory before you can really know whats going on in the first place. The key is that to truly understand routing and switching processes, youve got to have that hands-on experience.

So if the simulator questions are the more obvious reason to get hands-on experience, what are the less obvious reasons?

Glad you asked!

You see what happens when things dont go according to the script. One of the biggest problems with learning your skills on software programs such as router simulators is that with simulators, things go pretty much as planned.

I have news for you: that doesnt always happen in the real world. While Cisco routers and switches are highly reliable devices, every once in a while youre going to get an unexpected result from a command. Maybe it didnt work after you typed it in maybe it has an effect on your prior configuration that you didnt expect. Maybe you dont know what happened you just typed in that command and the router went nuts!

Sooner or later, thats going to happen to you in the real world. And as I tell my students, its actually a good thing to have happen to you in a lab.

You dont learn to troubleshoot or fine-tune a configuration when everything works perfectly. You dont learn much at all when things go perfectly. And youre practicing to learn!

I often say that great chefs dont learn to cook on cooking simulators they learn in the kitchen, and they burn a lot of meals on the way to greatness. You need to screw up some configs on the way to greatness, and you cant do that on a computer program. You have to be on the real thing.

You build confidence by working with real Cisco routers and switches. Would you want the Super Bowl to be the first football game you ever really played in? Of course not. Then why would you take router configuration exams and be nervous about having to create a VLAN, or troubleshoot an OSPF configuration?

You cannot walk into the testing room a nervous wreck. You must have the attitude that you are already a CCNA or CCNP, and youre just there to make it official. I can tell you from firsthand experience with many students that the way you develop than confidence is to work with the real deal.

You cant buy that confidence, and you cant simulate your way to it. Youve got to work with real Cisco routers and switches. By working with the real equipment, you develop the real skills and real confidence you need to pass the CCNA and CCNP exams.

About The Author

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage. The Bryant Advantage sells the world's best CCNA Study Guide in PDF format for only $15 and is the ONLY company specializing in CCNA and CCNP rack rentals, allowing candidates for these certifications to gain vital hands-on experience with full racks of Cisco routers and switches with labs and prices designed just for them. There are also plenty of FREE CCNA and CCNP tutorials! Visit his site at www.thebryantadvantage.com today!

chris@thebryantadvantage.com

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Cisco Certification: The OSI Model Isn't Just For Exams Anymore!

There's nothing I enjoy more than teaching Cisco technologies, especially CCNA candidates. Whether it's in-person or online, everyone's excited to be there. There's a sense of anticipation in the air, and everyone is ready to work hard, get their hands on the racks of Cisco routers and switches I have available...

... and then I break out the OSI model chart. Chins slump. People sigh, or at least wish they hadn't ordered decaf that morning. Okay, it's not that bad. But it does temper the excitement a little. I always get a sense of "why can't we just hurry up and get on the routers and switches? Why do we have to learn this dry stuff?" One reason is that Cisco demands you know the OSI model inside and out for both the Intro and ICND exams. You have to admit that's a pretty good reason, but still, students find the OSI model information to be very dry.

I understand that, because I've been there. My first exposure to the OSI model was actually in a Novell "Networking Technologies" class, and man, was that chart ever dry. They crammed every known protocol (and some unknown ones, I think) into the OSI model. It looked like a giant jigsaw puzzle, and the real problem is that I didn't know what the heck most of that stuff was.

So I dutifully attempted to memorize this massive chart. I managed to pass the exam, but I wondered what all that effort had really been for. It's not like you sit around in a server room or wiring closet and discuss the OSI model.

As a CCNA candidate, you don't have to worry about all the protocols I memorized way back when, but you do have to know what happens at each layer. Which leads to this question:

"If I work with routers and switches, why do I have to know about all the other layers? Don't routers and switches just work at layer 2 and 3?"

Yes, switches work at Layer 2 and routers at Layer 3. But to truly understand networking, you've got to understand what happens at the other layers. Why?

Most network administrators and engineers are going to spend a lot more time troubleshooting than installing. That's just the way it is. And to troubleshoot effectively, you've got to know what's going on at all layers of the OSI model, not just layers 2 and 3. As someone who's done a lot of hiring and conducted a great many job interviews, I can tell you that the ability to troubleshoot is the number one quality I look for.

That's why I tell CCNA and CCNP candidates that they've got to get all the hands-on practice they can; while I understand the importance of theory, the only way to develop troubleshooting ability is to work on the real deal. No simulator program is going to teach you how to troubleshoot.

Additionally, the only way to truly develop your troubleshooting abilities is to know what's going on over the entire network, not just the routers and switches. Troubleshooting always starts at Layer 1; if you don't find a problem at the Physical layer, and everything's fine with your routers and switches, how are you going to continue troubleshooting if you don't know what the next steps are as data moves closer to the end user?

So when it comes to the OSI model, don't just give it a quick once-over and move on to the fun stuff in your CCNA studies. The tangible benefit of passing your exams is great, but it's the hidden benefit of developing your own troubleshooting methodology that makes mastering the OSI model worthwhile.

About The Author

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage. The Bryant Advantage sells the world's most comprehensive CCNA Study Guide in the world, and is the ONLY company specializing in CCNA and CCNP rack rentals, allowing candidates for these certifications to gain vital hands-on experience with full racks of Cisco routers and switches with labs and prices designed just for them. There are also plenty of FREE CCNA and CCNP tutorials! Visit his site at www.thebryantadvantage.com today!

chris@thebryantadvantage.com

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What To Expect At The Cisco Testing Centerwww.

Sim.com Candidates can register for the CCNA exam (640-801 exam or 640-821 INTRO or 640-811 ICND ) at Pearson VUE or Prometric testing centers.

In order to do their best, candidates should know what to expect at the testing center for the Cisco CCNA certification exam. Since testing center guidelines may vary from one center to another, we recommend that the candidates call the local testing center to check about the guidelines. Here are some points providing information on what you can expect at the exam center:

Re-certification: If you have taken a Cisco CCNA certification exam before, find out your Cisco ID and specify it before you start with your registration. This will ensure that you get proper credit for the exam and will help avoid any duplicate records.

Reach before time: We strongly suggest reaching the test center before time. Failure to do so may result in cancellation of the appointment.

Sign the logbook: You may be asked to sign-in the logbook upon arrival as well as upon departure. Do check on this.

You must carry your identification: You will be required to show a valid identification (ID), perhaps including a recent, recognizable photograph. If the supervisor questions your ID, you may be required to show another ID. You should check the testing center guidelines on identification and take all supplemental identification documents with you.

Generally Accepted Identification:

Passport

Photobearing driver's license with signature

National/Military identification card

The following MAY not be accepted as valid ID:

Credit Cards (Please check with test center)

Private identification cards

Any expired ID

Read the testing center regulation form carefully: You will be provided with a Testing Center Regulation form by the supervisor. Read the regulations carefully and comply with them during the test.

Sign the confidentiality statement: The supervisor is responsible for asking you to sign the confidentially statement at the test center indicating that you will not reveal exam questions to other students after the test.

Supervisor sets up your test computer: The supervisor will ensure that the Cisco certification test displays on screen before handing over the machine to you.

Ask for sheets for scratch work: Scratch papers will be provided to you at the testing center. These are sometimes only available on request. Ask for some blank scratch sheets to do calculations and rough work. Jot down important points and tables (such as powers of 2, binary representation tables etc) before exam starts. This can be a big time saver. Do not take the scratch paper out of the testing room on completion of exam.

Items not allowed in the testing room: The candidate is not allowed to bring in the testing room personal items such as:

Books, revision sheets or notes: The exam is closed book

Cellular phones & alarms

Food or drinks may not be allowed

Calculators

Your session may be audio and video taped: Do not attempt to talk or communicate in any form to anybody in the testing room. Your session may be taped and can lead to immediate disqualification .

On exam completion: You will be explained by the supervisor what to do when you complete the exam. If not, or if you are unclear about what you should do, ask it yourself before beginning the exam.

Do not take with you the the testing material from the testing room: Return all of your testing materials, including the scrap paper, on the completion of your exam to the supervisor.

Certified copy of the exam result: Your supervisor will give you a certified copy of the exam report on completion of the test. This will list your score indicating strengths and weaknesses in the various test areas. Ask the supervisor for the certified copy, if you do not get it.

About The Author

SemSim.com provides training resources for Cisco certification exams: CCIE, CCNP, CCNA, CCDP, CCDA. It offers FREE learning resources to students such as study guides and router simulation labs. For more information visit: http://www.SemSim.com : Making Cisco cetification easy!

support@semsim.com

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Cisco Certification: The Cisco Three-Layered Hierarchical Modelwww.

Sim.com Cisco has defined a hierarchical model known as the hierarchical internetworking model. This model simplifies the task of building a reliable, scalable, and less expensive hierarchical internetwork because rather than focusing on packet construction, it focuses on the three functional areas, or layers, of your network:

Core layer: This layer is considered the backbone of the network and includes the high-end switches and high-speed cables such as fiber cables. This layer of the network does not route traffic at the LAN. In addition, no packet manipulation is done by devices in this layer. Rather, this layer is concerned with speed and ensures reliable delivery of packets.

Distribution layer: This layer includes LAN-based routers and layer 3 switches. This layer ensures that packets are properly routed between subnets and VLANs in your enterprise. This layer is also called the Workgroup layer.

Access layer: This layer includes hubs and switches. This layer is also called the desktop layer because it focuses on connecting client nodes, such as workstations to the network. This layer ensures that packets are delivered to end user computers.

Figure INT.2.1 displays the three layers of the Cisco hierarchical model.

When you implement these layers, each layer might comprise more than two devices or a single device might function across multiple layers.The benefits of the Cisco hierarchical model include:

High Performance: You can design high performance networks, where only certain layers are susceptible to congestion.

Efficient management & troubleshooting: Allows you to efficiently organize network management and isolate causes of network trouble.

Policy creation: You can easily create policies and specify filters and rules.

Scalability: You can grow the network easily by dividing your network into functional areas.

Behavior prediction: When planning or managing a network, the model allows you determine what will happen to the network when new stresses are placed on it.