Your CCNA studies are going to include quite a bit of information about switches, and for good reason. if you don't understand basic switching theory, you can't configure and troubleshoot Cisco switches, either on the CCNA exam or in the real world. That goes double for trunking!
Trunking is simply enabling two or more switches to communicate and send frames to each other for transmission to remote hosts. There are two major trunking protocols that we need to know the details of for exam success and real-world success, but before we get to the protocols, let's discuss the cables we need.
Connecting two Cisco switches requires a crossover cable. As you know, there are eight wires inside an ethernet cable. In a crossover cable, four of the cables "cross over" from one pin to another. For many newer Cisco switches, all you need to do to create a trunk is connect the switches with a crossover cable. For instance, 2950 switches dynamically trunk once you connect them with the right cable. If you use the wrong cable, you'll be there a while!
There are two different trunking protocols in use on today's Cisco switches, ISL and IEEE 802.1Q, generally referred to as "dot1q". There are three main differences between the two. First, ISL is a Cisco-proprietary trunking protocol, where dot1q is the industry standard. (Those of you new to Cisco testing should get used to the phrases "Cisco-proprietary" and "industry standard".) If you're working in a multivendor environment, ISL may not be a good choice. And even though ISL is Cisco's own trunking protocol, some Cisco switches run only dot1q.
ISL also encapsulates the entire frame, increasing the network overhead. Dot1q only places a header on the frame, and in some circumstances, doesn't even do that. There is much less overhead with dot1q as compared to ISL. That leads to the third major difference, the way the protocols work with the native vlan.
The native vlan is simply the default vlan that switch ports are placed into if they are not expressly placed into another vlan. On Cisco switches, the native vlan is vlan 1. (This can be changed.) If dot1q is running, frames that are going to be sent across the trunk line don't even have a header placed on them; the remote switch will assume that any frame that has no header is destined for the native vlan.
The problem with ISL is that is doesn't understand what a native vlan is. Every single frame will be encapsulated, regardless of the vlan it's destined for.
Switching theory is a big part of your CCNA studies, and it can seem overwhelming at first. Just break your studies down into smaller, more manageable parts, and soon you'll see the magic letters "CCNA" behind your name!
Tuesday, September 14, 2010
Cisco CCNA Certification: Defining Broadcast Domains
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!
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!
Cisco CCNA / CCNP Home Lab Tutorial: The 2501 Router
To be truly prepared for your CCNA and CCNP exams, you need real hands-on experience with real Cisco routers and switches. However, a production network is a really bad place to practice your configurations, but an excellent way to get fired and/or sued. The key to becoming a true CCNA and CCNP is assembling your own Cisco home lab.
You don't have to spend a lot of money to do so; used Cisco equipment is cheaper than ever. It's robust as well - I've bought literally hundreds of used routers and switches over the years and have had very few problems. I owe much of my skill to practicing configurations and troubleshooting in my own home lab.
2501 routers are fantastic for CCNA and CCNP home labs. They come with two serial interfaces, allowing you to connect one interface directly to another router (you'll need a DTE/DCE cable for that, too) while connecting another to a frame relay switch if you like. If you don't have a frame relay switch, you can connect a 2501 directly to two other routers via the serial interfaces.
You also have an AUI port, which requires a transceiver to operate as your Ethernet interface. Transceivers are pretty cheap and readily available from Cisco resellers and ebay vendors, so pick one up for each 2503 you decide to buy.
2501 routers don't come with BRI interfaces, but not every router in your lab has to be ISDN-ready. If you choose not to have ISDN in your lab at all, 2501s are the way to go. If you do want to run ISDN and have an ISDN simulator device, you can get two 2503s and the rest of your routers can be 2501.
All in all, 2501 routers are great for your CCNA / CCNP home lab. They cost less than $100 each on ebay, so they're also very affordable. There's no better training than training on your own CCNA or CCNP home lab, and you can always sell the equipment later if you like. Basically, you're renting the routers and switches, and the experience you get by working with the real deal is invaluable.
You don't have to spend a lot of money to do so; used Cisco equipment is cheaper than ever. It's robust as well - I've bought literally hundreds of used routers and switches over the years and have had very few problems. I owe much of my skill to practicing configurations and troubleshooting in my own home lab.
2501 routers are fantastic for CCNA and CCNP home labs. They come with two serial interfaces, allowing you to connect one interface directly to another router (you'll need a DTE/DCE cable for that, too) while connecting another to a frame relay switch if you like. If you don't have a frame relay switch, you can connect a 2501 directly to two other routers via the serial interfaces.
You also have an AUI port, which requires a transceiver to operate as your Ethernet interface. Transceivers are pretty cheap and readily available from Cisco resellers and ebay vendors, so pick one up for each 2503 you decide to buy.
2501 routers don't come with BRI interfaces, but not every router in your lab has to be ISDN-ready. If you choose not to have ISDN in your lab at all, 2501s are the way to go. If you do want to run ISDN and have an ISDN simulator device, you can get two 2503s and the rest of your routers can be 2501.
All in all, 2501 routers are great for your CCNA / CCNP home lab. They cost less than $100 each on ebay, so they're also very affordable. There's no better training than training on your own CCNA or CCNP home lab, and you can always sell the equipment later if you like. Basically, you're renting the routers and switches, and the experience you get by working with the real deal is invaluable.
Monday, September 13, 2010
Cisco CCNA / CCNP Home Lab Tutorial: The 2503 Router
I know from experience that part of the excitement and anxiety of putting together your own CCNA / CCNP home lab is deciding what to buy! While you can make a workable home lab out of almost any combination of Cisco routers and switches, some routers are better suited for home lab work than others because they can fill multiple roles.
When you buy CCNA or CCNP "lab kits" - bundles of routers and switches - you can get a little confused about whether you're getting a good deal. One router I get asked about quite a bit is the 2503.
2503 routers are fantastic for CCNA and CCNP home labs. They come with two serial interfaces, allowing you to connect one interface directly to another router (you'll need a DTE/DCE cable for that, too) while connecting another to a frame relay switch if you like. If you don't have a frame relay switch, you can connect a 2503 directly to two other routers via the serial interfaces.
You also have an AUI port, which requires a transceiver to operate as your Ethernet interface. Transceivers are pretty cheap and readily available from Cisco resellers and ebay vendors, so pick one up for each 2503 you decide to buy.
2503 routers also come with a BRI interface. Even though you may not have an ISDN simulator right now, you may choose to add one later. That makes a 2503 a great bet for future lab expansion.
All in all, 2503 routers are great for your CCNA / CCNP home lab. They run about $125 each on ebay, or less, so they're also very affordable. There's no better training than training on your own CCNA or CCNP home lab, and you can always sell the equipment later if you like. Basically, you're renting the routers and switches, and the experience you get by working with the real deal is invaluable.
When you buy CCNA or CCNP "lab kits" - bundles of routers and switches - you can get a little confused about whether you're getting a good deal. One router I get asked about quite a bit is the 2503.
2503 routers are fantastic for CCNA and CCNP home labs. They come with two serial interfaces, allowing you to connect one interface directly to another router (you'll need a DTE/DCE cable for that, too) while connecting another to a frame relay switch if you like. If you don't have a frame relay switch, you can connect a 2503 directly to two other routers via the serial interfaces.
You also have an AUI port, which requires a transceiver to operate as your Ethernet interface. Transceivers are pretty cheap and readily available from Cisco resellers and ebay vendors, so pick one up for each 2503 you decide to buy.
2503 routers also come with a BRI interface. Even though you may not have an ISDN simulator right now, you may choose to add one later. That makes a 2503 a great bet for future lab expansion.
All in all, 2503 routers are great for your CCNA / CCNP home lab. They run about $125 each on ebay, or less, so they're also very affordable. There's no better training than training on your own CCNA or CCNP home lab, and you can always sell the equipment later if you like. Basically, you're renting the routers and switches, and the experience you get by working with the real deal is invaluable.
Certification Q&A: The Basics Of Certification
* What does certified mean?
There are four accepted meanings of the adjective “certified” but only two of which satisfy the needed meaning. To be certified means to be endorsed with authority by an institution or a person with higher position after one successfully meets certain requirements. Another meaning is that a person is qualified to do a certain job as supported by an appropriate document better known and regarded as a Certification.
* What certifications are there?
If you are pertaining to online certifications, there are lots to be traced. To help you find one best certification that fits your ability and interest, you may log on to reliable sites in the internet. For now, the following are the basic IT certifications:
• IT Auditing
• Document Imaging
• E-Commerce
• Internet/Intranet
• Linux
• Networking
• Printing
• Project Management
• IT Security
• Servers
• Service Technician
• Technical Trainer
• Webmaster
* Who benefits from certification?
Primarily the one given a certification benefits more. Being certified means one can properly function on a certain job. This means, companies will easily hire a person with certification especially when certifications come from a reliable learning institution.
In some ways, the company to which a certified person intends to apply for work will also benefit since the performance of the applying employee is being supported with a certification.
* Is certification better than experience?
The answer for that is a big "No." Certification means training. It is impossible for a person to send himself training without experiencing what it is he intends to do. For this reason, we cannot equate certification from experience since they do not share the same purpose. However, if you already have work experience, a certification is a big help for promotion, recognition and pay raises.
On the other hand, companies are not solely after experience but after educational attainments and performances. In other words, having completed a course as proved by a certification is a chance to be hired.
* Which certification program is best for me?
The best certification program for you is the one that fits your interests and capabilities. Those two factors should be considered above all ese when finding the right and best certification program for you.
* How much will getting certified cost?
Almost all training packages from different training institutions are cost effective. The training cost will depend on the training you want to pursue and in which training institution you intend to enroll. Generally, a trainee should prepare to pay between $100 and $400 for each training program.
* How long will certification take?
There are training institutions that offer a 6-month online training program. The usual training timeframe is one year. This length of training may exceed to a maximum of 2 years depending on the program conducted.
* Do I need a college degree to be certified?
You do not need a college degree to be certified. Some certification programs require one to have at least finished high school upon enrolling in a certain course.
* Will certification really help my career?
A certification may help your career. Nowadays, competition in the jobs is getting tougher. For one to stay in his or her job or to be promoted to a higher position, one factor to consider is his or her educational achievements. That is one reason why mastering your field of work by means of studying and training can be a great boost for your career. That is where a certification program can make or break your career advancement.
* Will I have to go somewhere for my certification training?
While you can find local institutions where you can take classes and tests, most training is done online now. You do not need to go somewhere else for your training. You do not even need to attend classes personally for your lessons. Not only is training done mostly online now, but examinations for certification are also given online.
There are four accepted meanings of the adjective “certified” but only two of which satisfy the needed meaning. To be certified means to be endorsed with authority by an institution or a person with higher position after one successfully meets certain requirements. Another meaning is that a person is qualified to do a certain job as supported by an appropriate document better known and regarded as a Certification.
* What certifications are there?
If you are pertaining to online certifications, there are lots to be traced. To help you find one best certification that fits your ability and interest, you may log on to reliable sites in the internet. For now, the following are the basic IT certifications:
• IT Auditing
• Document Imaging
• E-Commerce
• Internet/Intranet
• Linux
• Networking
• Printing
• Project Management
• IT Security
• Servers
• Service Technician
• Technical Trainer
• Webmaster
* Who benefits from certification?
Primarily the one given a certification benefits more. Being certified means one can properly function on a certain job. This means, companies will easily hire a person with certification especially when certifications come from a reliable learning institution.
In some ways, the company to which a certified person intends to apply for work will also benefit since the performance of the applying employee is being supported with a certification.
* Is certification better than experience?
The answer for that is a big "No." Certification means training. It is impossible for a person to send himself training without experiencing what it is he intends to do. For this reason, we cannot equate certification from experience since they do not share the same purpose. However, if you already have work experience, a certification is a big help for promotion, recognition and pay raises.
On the other hand, companies are not solely after experience but after educational attainments and performances. In other words, having completed a course as proved by a certification is a chance to be hired.
* Which certification program is best for me?
The best certification program for you is the one that fits your interests and capabilities. Those two factors should be considered above all ese when finding the right and best certification program for you.
* How much will getting certified cost?
Almost all training packages from different training institutions are cost effective. The training cost will depend on the training you want to pursue and in which training institution you intend to enroll. Generally, a trainee should prepare to pay between $100 and $400 for each training program.
* How long will certification take?
There are training institutions that offer a 6-month online training program. The usual training timeframe is one year. This length of training may exceed to a maximum of 2 years depending on the program conducted.
* Do I need a college degree to be certified?
You do not need a college degree to be certified. Some certification programs require one to have at least finished high school upon enrolling in a certain course.
* Will certification really help my career?
A certification may help your career. Nowadays, competition in the jobs is getting tougher. For one to stay in his or her job or to be promoted to a higher position, one factor to consider is his or her educational achievements. That is one reason why mastering your field of work by means of studying and training can be a great boost for your career. That is where a certification program can make or break your career advancement.
* Will I have to go somewhere for my certification training?
While you can find local institutions where you can take classes and tests, most training is done online now. You do not need to go somewhere else for your training. You do not even need to attend classes personally for your lessons. Not only is training done mostly online now, but examinations for certification are also given online.
CCNA / CCNP Home Lab Tutorial: The VLAN.DAT File
CCNA and CCNP candidates who have their own Cisco home labs often email me about an odd situation that occurs when they erase a switch's configuration. Their startup configuration is gone, as they expect, but the VLAN and VTP information is still there!
Sounds strange, doesn't it? Let's look at an example. On SW1, we run show vlan brief and see in this abbreviated output that there are three additional vlans in use:
SW1#show vlan br
10 VLAN0010 active
20 VLAN0020 active
30 VLAN0030 active
We want to totally erase the router's startup configuration, so we use the write erase command, confirm it, and reload without saving the running config:
SW1#write erase
Erasing the nvram filesystem will remove all configuration files! Continue?
[confirm]
[OK]
Erase of nvram: complete
00:06:00: %SYS-7-NV_BLOCK_INIT: Initalized the geometry of nvram
SW1#reload
System configuration has been modified. Save? [yes/no]: n
Proceed with reload? [confirm]
The router reloads, and after exiting setup mode, we run show vlan brief again. And even though the startup configuration was erased, the vlans are still there!
Switch#show vlan br
10 VLAN0010 active
20 VLAN0020 active
30 VLAN0030 active
The reason is that this vlan and VTP information is actually kept in the VLAN.DAT file in Flash memory, and the contents of Flash are kept on a reload. The file has to be deleted manually.
There's a little trick to deleting this file. The switch will prompt you twice to ask if you really want to get rid of this file. Don't type "y" or "yes"; just accept the defaults by hitting the return key. If you type "y", the router attempts to delete a file named "y", as shown here:
Switch#delete vlan.dat
Delete filename [vlan.dat]? y
Delete flash:y? [confirm]
%Error deleting flash:y (No such file or directory)
Switch#delete vlan.dat
Delete filename [vlan.dat]?
Delete flash:vlan.dat? [confirm]
Switch#
The best way to prepare for CCNA and CCNP exam success is by working on real Cisco equipment, and by performing lab tasks over and over. Repetition is the mother of skill, and by truly erasing your VLAN and VTP information by deleting the vlan.dat file from Flash, you'll be building your Cisco skills to the point where your CCNA and CCNP exam success is a certainty.
Sounds strange, doesn't it? Let's look at an example. On SW1, we run show vlan brief and see in this abbreviated output that there are three additional vlans in use:
SW1#show vlan br
10 VLAN0010 active
20 VLAN0020 active
30 VLAN0030 active
We want to totally erase the router's startup configuration, so we use the write erase command, confirm it, and reload without saving the running config:
SW1#write erase
Erasing the nvram filesystem will remove all configuration files! Continue?
[confirm]
[OK]
Erase of nvram: complete
00:06:00: %SYS-7-NV_BLOCK_INIT: Initalized the geometry of nvram
SW1#reload
System configuration has been modified. Save? [yes/no]: n
Proceed with reload? [confirm]
The router reloads, and after exiting setup mode, we run show vlan brief again. And even though the startup configuration was erased, the vlans are still there!
Switch#show vlan br
10 VLAN0010 active
20 VLAN0020 active
30 VLAN0030 active
The reason is that this vlan and VTP information is actually kept in the VLAN.DAT file in Flash memory, and the contents of Flash are kept on a reload. The file has to be deleted manually.
There's a little trick to deleting this file. The switch will prompt you twice to ask if you really want to get rid of this file. Don't type "y" or "yes"; just accept the defaults by hitting the return key. If you type "y", the router attempts to delete a file named "y", as shown here:
Switch#delete vlan.dat
Delete filename [vlan.dat]? y
Delete flash:y? [confirm]
%Error deleting flash:y (No such file or directory)
Switch#delete vlan.dat
Delete filename [vlan.dat]?
Delete flash:vlan.dat? [confirm]
Switch#
The best way to prepare for CCNA and CCNP exam success is by working on real Cisco equipment, and by performing lab tasks over and over. Repetition is the mother of skill, and by truly erasing your VLAN and VTP information by deleting the vlan.dat file from Flash, you'll be building your Cisco skills to the point where your CCNA and CCNP exam success is a certainty.
CCNA
CCNA stands for Cisco Certified Network Associate - a certification for IT professionals that is issued by Cisco Systems, Inc., one of the most successful computer networking companies. Cisco manufactures and markets a wide range of devices for both enterprises and telecommunications carriers. Cisco is an abbreviation of San FranCISCO.
The Cisco Certified Network Associate is an apprentice, or foundation level (along with Cisco Certified Design Associate), within the three levels of certification that include Associate, Professional, and Expert. Basically, CCNA professionals are certified to install, configure, and operate LAN, WAN, and dial access services for small networks (100 nodes or fewer), including but not exclusive to use of these protocols: IP, IGRP, Serial, Frame Relay, IP RIP, VLANs, RIP, Ethernet, and Access Lists. The certification is valid for three years, after which recertification may be sought.
In order to hold a CCNA certification, a candidate has to pass either the Cisco Certified Network Associate Exam or a combination of Introduction to Cisco Networking Technologies Exam and Interconnecting Cisco Networking Devices Exam. Main topics for these three exams include Planning and Designing; Design and Support; Implementation and Operation; Troubleshooting; and Technology. Other related topics may also appear on any specific delivery of the exam.
There are also some recommended training programs that may be taken before the above-mentioned examinations. These programs include Introduction to Cisco Networking Technologies (INTRO), Interconnecting Cisco Network Devices (ICND), and Additional Training (CCNA Prep Center Pilot). These trainings incorporate topics such as fundamental knowledge and comprehension of networking; how to select, connect, configure, and troubleshoot the various Cisco networking devices; sample questions, simulations, e-learning modules, labs, tips, etc.
The Cisco Certified Network Associate is an apprentice, or foundation level (along with Cisco Certified Design Associate), within the three levels of certification that include Associate, Professional, and Expert. Basically, CCNA professionals are certified to install, configure, and operate LAN, WAN, and dial access services for small networks (100 nodes or fewer), including but not exclusive to use of these protocols: IP, IGRP, Serial, Frame Relay, IP RIP, VLANs, RIP, Ethernet, and Access Lists. The certification is valid for three years, after which recertification may be sought.
In order to hold a CCNA certification, a candidate has to pass either the Cisco Certified Network Associate Exam or a combination of Introduction to Cisco Networking Technologies Exam and Interconnecting Cisco Networking Devices Exam. Main topics for these three exams include Planning and Designing; Design and Support; Implementation and Operation; Troubleshooting; and Technology. Other related topics may also appear on any specific delivery of the exam.
There are also some recommended training programs that may be taken before the above-mentioned examinations. These programs include Introduction to Cisco Networking Technologies (INTRO), Interconnecting Cisco Network Devices (ICND), and Additional Training (CCNA Prep Center Pilot). These trainings incorporate topics such as fundamental knowledge and comprehension of networking; how to select, connect, configure, and troubleshoot the various Cisco networking devices; sample questions, simulations, e-learning modules, labs, tips, etc.
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