Wednesday, December 31, 2008

Cisco CCNA Certification: How And Why Switches Trunk

Cisco CCNA Certification: How And Why Switches Trunk
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! Stumble Upon Toolbar

Cisco CCNA Certification: The (Many) Different Kinds Of Switching

Cisco CCNA Certification: The (Many) Different Kinds Of Switching
When you're studying for your CCNA exam, whether you're taking the Intro-ICND path or the single-exam path, you're quickly introduced to the fact that switching occurs at Layer 2 of the OSI model. No problem there, but then other terms involving switching are thrown in, and some of them can be more than a little confusing. What is "cell switching"? What is "circuit switching"? Most confusing of all, how can you have "packet switching"? Packets are found at Layer 3, but switching occurs at Layer 2. How can packets be switched?

Relax! As you'll see in this article, the terms aren't that hard to keep straight. Packet switching, for example, describes a protocol that divides a message into packets before they're sent. The packets are then sent individually, and may take different paths to the same destination. Once the packets arrive at the final destination, they are reassembled.

Frame switching follows the same process, but at a different layer of the OSI model. When the protocol runs at Layer 2 rather than Layer 3, the process is referred to as frame switching.

Cell switching also does much the same thing, but as the name implies, the device in use is a cell switch. Cell-switched packets are fixed in length. ATM is a popular cell-switching technology.

The process of circuit switching is just a bit different, in that the process of setting up the circuit itself is part of the process. The channel is set up between two parties, data is transmitted, and the channel is then torn down. The circuit-switching technology most familiar to CCNA candidates is ISDN.

Don't let these terms confuse you. The four different terms are describing much the same process. The main difference is that they are occurring at different levels of the OSI model, and using a different transport method to get the data where it needs to go. Stumble Upon Toolbar

Tuesday, December 30, 2008

Cisco Ccna Certification Training Tips

Cisco Ccna Certification Training Tips
Cisco is a famous and large supplier of all types of networking hardware and software including security and router products. The company offers many job opportunities; but to become a member of Cisco, you have to undergo some form of Cisco training. It is only after doing some Cisco training that you will become a Cisco certified Network Associate. With Cisco training, you learn all that is needed about necessary foundation and get a better understanding of IP networking and troubleshooting. And with this Cisco training, you become better prepared to answer the CCNA Routing and Switching Certification, and pass it to get your certificate.

CISCO Training Centers

The first thing you have to do to get Cisco training is to choose the Cisco training center you want to join. Once you have done the required research and chosen the right training center, you will have to first read and accept the terms of the Cisco Career Trainings and Confidentiality Agreement. The reason you have to agree to this agreement is so that Cisco can prevent you from sharing their information with outside sources. And in case you don't agree with the agreement, then your application for Cisco training will not be processed. Once the terms of the agreement are agreed upon, you can start on your Cisco training. Your Cisco training basically consists of teaching you to get a better understanding of the operations and functions of LAN, WAN, VPN, SAN and Cisco IOS fundamentals. In addition to this, there are other topics that are necessary, and will be covered in your Cisco training.

Practice Exams and Prep Centers for CCNA Certification

These topics include the technology and testing for Cisco equipment. There are many practice exams you have to complete after the Cisco training, where these exams are taken like most exams, timed. The best place to visit to learn more about Cisco training is Cisco's website. You will find information here about the CCNA certification training and when exams are scheduled. In addition to this, you find many other types of certificates with descriptions of the certificates and requirements required to get them in this website. There is also a prep center you can join to get the required CCNA certification training with which you will be able to pass the 55-65 question tests. Remember that this is a Cisco system certification; so you have to use your best bet in taking Cisco training courses from them to be successful in getting the certificate.

Becoming a Cisco Certified Network Associate

Once you complete your Cisco training, you are automatically considered to be a Cisco Certified Network Associate where you will be able to configure, install and operate LAN, WAN and dial access services that are used for small networks. In addition to this, Cisco training will make you competent for IP, Serial, IP RIP, Ethernet, Frame Relay, VLAN and Access lists.

So if this is what you intend to make of your career, then you will have to undergo efficient Cisco training to become a Cisco Certified Network Associate where you will be provided with employment wherever you go. Stumble Upon Toolbar

How A Cisco Network Engineer Can Shape The World

How A Cisco Network Engineer Can Shape The World
When asked what you wanted to be when you grew up, you probably didn’t say a Cisco network engineer. In fact, unless you had a computer geek or an engineer in your family, you probably didn’t say an engineer at all. Kids usually want to be things that they see as glamorous models of people who change their world: firefighters, athletes, and even teachers. But as you grow up and start to learn about the way that the world really works, you realize that these aren’t the only jobs that shape the world. You start to consider work that’s both world-shaping and has duties that actually appeal to you. If you like computers, technology and problem solving, you might consider becoming a Cisco network engineer. And if you do, you might discover that your actions do help to improve the world around you.

The Cisco network engineer resolves computer problems for individuals and businesses that are using Cisco routers. This is a specialized practice but one that is more applicable to the world around you than you might think. Cisco is a brand name, which leads the industry in Internet networking. This means that if you’ve got computers networked together in a business of any size, there’s a good chance that Cisco’s technology is part of the system. If you’re able to troubleshoot and repair any problems that come up in that network, you can provide an important service that can keep that business up-and-running all throughout the year. In a world that relies on regular communication between computers to keep things running smoothly, this service can affect thousands of people at once.

The job of a Cisco network engineer is to know these systems inside and out. The most common thing that you will do if you get this kind of job is troubleshooting and computer repair. By learning the workings of the system, you’ll be able to identify what the problems are as they arise and how to fix them rapidly so that the business can keep its employees productive and its clients happy. But this isn’t all that you’ll do as a Cisco network engineer. You’ll also learn about new technology that is put out by the networking industry so that you can teach people how to incorporate it into their systems. You’ll learn how to install, configure and subnet new Cisco routers and switches. Basically, you’ll get to spend all day playing with computers. That’s a job that more and more kids these days think they might want to have.

So what would you tell a kid who said that they wanted to get this kind of job? In other words, how do you become a Cisco network engineer? Although some people teach themselves this kind of work on their own and others learn on-the-job as they’re moving up in the business world, there’s a much more efficient way to get the skills that you need to get this type of job. You can go to school to get a degree to become a Cisco network engineer. There are degree programs that actually teach you the hands-on specifics of how to work with these types of systems.

With this kind of credibility behind you, you should have no trouble getting the job that you want. It may not be quite what you thought you’d be doing when you were six but when you think about it, it’s probably even cooler! And now that you have a better understanding of the way that the world around you really works, you probably know that these kinds of jobs are the ones that really make a difference to people on a day-to-day basis. Stumble Upon Toolbar

Monday, December 29, 2008

Cisco CCNA / CCNP Certification: Ospf E2 vs. E1 Routes

Cisco CCNA / CCNP Certification: Ospf E2 vs. E1 Routes
OSPF is a major topic on both the CCNA and CCNP exams, and it's also the topic that requires the most attention to detail. Where dynamic routing protocols such as RIP and IGRP have only one router type, a look at a Cisco routing table shows several different OSPF route types.

R1#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

In this tutorial, we'll take a look at the difference between two of these route types, E1 and E2.

Route redistribution is the process of taking routes learned via one routing protocol and injecting those routes into another routing domain. (Static and connected routes can also be redistributed.) When a router running OSPF takes routes learned by another routing protocol and makes them available to the other OSPF-enabled routers it's communicating with, that router becomes an Autonomous System Border Router (ASBR).

Let's work with an example where R1 is running both OSPF and RIP. R4 is in the same OSPF domain as R1, and we want R4 to learn the routes that R1 is learning via RIP. This means we have to perform route redistribution on the ASBR. The routes that are being redistributed from RIP into OSPF will appear as E2 routes on R4:

R4#show ip route ospf

O E2 5.1.1.1 [110/20] via 172.34.34.3, 00:33:21, Ethernet0

6.0.0.0/32 is subnetted, 1 subnets

O E2 6.1.1.1 [110/20] via 172.34.34.3, 00:33:21, Ethernet0

172.12.0.0/16 is variably subnetted, 2 subnets, 2 masks

O E2 172.12.21.0/30 [110/20] via 172.34.34.3, 00:33:32,
Ethernet0

O E2 7.1.1.1 [110/20] via 172.34.34.3, 00:33:21, Ethernet0

15.0.0.0/24 is subnetted, 1 subnets

O E2 15.1.1.0 [110/20] via 172.34.34.3, 00:33:32, Ethernet0

E2 is the default route type for routes learned via redistribution. The key with E2 routes is that the cost of these routes reflects only the cost of the path from the ASBR to the final destination; the cost of the path from R4 to R1 is not reflected in this cost. (Remember that OSPF's metric for a path is referred to as "cost".)
In this example, we want the cost of the routes to reflect the entire path, not just the path between the ASBR and the destination network. To do so, the routes must be redistributed into OSPF as E1 routes on the ASBR, as shown here.

R1#conf t

Enter configuration commands, one per line. End with CNTL/Z.

R1(config)#router ospf 1

R1(config-router)#redistribute rip subnets metric-type 1

Now on R4, the routes appear as E1 routes and have a larger metric, since the entire path cost is now reflected in the routing table.

O E1 5.1.1.1 [110/94] via 172.34.34.3, 00:33:21, Ethernet0

6.0.0.0/32 is subnetted, 1 subnets

O E1 6.1.1.1 [110/100] via 172.34.34.3, 00:33:21, Ethernet0

172.12.0.0/16 is variably subnetted, 2 subnets, 2 masks

O E1 172.12.21.0/30 [110/94] via 172.34.34.3, 00:33:32, Ethernet0

O E1 7.1.1.1 [110/94] via 172.34.34.3, 00:33:21, Ethernet0

15.0.0.0/24 is subnetted, 1 subnets

O E1 15.1.1.0 [110/94] via 172.34.34.3, 00:33:32, Ethernet0

Knowing the difference between E1 and E2 routes is vital for CCNP exam success, as well as fully understanding a production router's routing table. Good luck in your studies! Stumble Upon Toolbar

Passing Cisco’s CCNA And CCNP Exams: Traceroute

Passing Cisco’s CCNA And CCNP Exams: Traceroute
In preparation for your CCNA and CCNP exam success, you've got to learn to troubleshoot Cisco routers. And while ping is a great basic IP connectivity tool, it doesn't give you all the information you need to diagnose network connectivity issues.

Let's say you have six routers between CityA and CityB. You send a ping from A to B, and get this return:

R1#ping 172.1.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.1.1.1, timeout is 2 seconds:

.....

Success rate is 0 percent (0/5)

The five periods indicate that there is no IP connectivity to CityB. Problem is, that's about all ping tells you. You can have 5 or 50 routers between the two points, so how can you tell which downstream router has the problem?

That's where traceroute comes in. Traceroute sends three datagrams with a Time To Live (TTL) of 1. Those datagrams will timeout once they hit the first router in the path, and that router will respond with an ICMP Time Exceeded message.

In response, the sending router sends three more datagrams, but these have a TTL of 2. This means that the next router in line will send back ICMP Time Exceeded messages. This process continues until the final destination (CItyB) is reached the output of the command shows us the path the data took:

Router1#traceroute 271.1.1.1

Type escape sequence to abort.

Tracing the route to 271.1.1.1

1 20.1.1.1 4 msec 4 msec 4 msec

2 30.1.1.1 20 msec 16 msec 16 msec

3 271.1.1.1 16 msec * 16 msec

How does this help troubleshoot a problem? Let's say that the second router in this path, 30.1.1.1, doesn't know how to get to 271.1.1.1. The output would look like this:

Router1#traceroute 271.1.1.1

Type escape sequence to abort.

Tracing the route to 271.1.1.1

1 20.1.1.1 4 msec 4 msec 4 msec

2 30.1.1.1 20 msec 16 msec 16 msec

3 * * *

This indicates that the router at 30.1.1.1 doesn't know how to get to the final destination. Now you have a better idea of which router has an issue!

Now here's the bad part: you're going to get 30 lines of three asterisks, and until you abort this traceroute, you're going to just watch those asterisks go across the screen. There's an abort sequence that the router mentions in the first line of the console output, but the router doesn't tell you what it is! So I will - this top-secret sequence is TWICE, one right after the other.

That keystroke takes a little getting used to, but a CCNA or CCNP can do it! Add this command to your Cisco skill set, and it will serve you well both on the CCNA and CCNP exams and your real-world networks. And you'll impress your friends by knowing how to stop a traceroute! Stumble Upon Toolbar

Sunday, December 28, 2008

Cisco CCNP Certification: The BGP Weight Attribute

Cisco CCNP Certification: The BGP Weight Attribute
When you're studying for the CCNP certification, especially the BSCI exam, you must gain a solid understanding of BGP. BGP isn't just one of the biggest topics on the BSCI exam, it's one of the largest. BGP has a great many details that must be mastered for BSCI success, and those of you with one eye on the CCIE must learn the fundamentals of BGP now in order to build on those fundamentals at a later time.

Path attributes are a unique feature of BGP. With interior gateway protocols such as OSPF and EIGRP, administrative distance is used as a tiebreaker when two routes to the same destination had different next-hop IP addresses but the same prefix length. BGP uses path attributes to make this choice.

The first attribute considered by BGP is weight. Weight is a Cisco-proprietary BGP attribute, so if you're working in a multivendor environment you should work with another attribute to influence path selection.

The weight attribute is significant only to the router on which it is changed. If you set a higher weight for a particular route in order to give it preference (a higher weight is preferred over a lower one), that weight is not advertised to other routers.

BGP uses categories such as "transitive", "non-transitive", "mandatory", and "optional" to classify attributes. Since weight is a locally significant Cisco-proprietary attribute, it does not all into any of these categories.

The weight can be changed on a single route via a route-map, or it can be set for a different weight for all routes received from a given neighbor. To change the weight for all incoming routes, use the "weight" option with the neighbor command after forming the BGP peer relationships.

R2(config)#router bgp 100

R2(config-router)#neighbor 100.1.1.1 remote-as 10

R2(config-router)#neighbor 100.1.1.1 weight 200

Learning all of the BGP attributes, as well as when to use them, can seem an overwhelming task when you first start studying for your BSCI and CCNP exams. Break this task down into small parts, learn one attribute at a time, and soon you'll have the BGP attributes mastered. Stumble Upon Toolbar

Cisco CCNA Certification: Broadcasts, Unicasts, And Multicasts

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 Stumble Upon Toolbar

Saturday, December 27, 2008

Cisco Certification: The "Secret" Key To Getting Your CCNA And CCNP

Cisco Certification: The "Secret" Key To Getting Your CCNA And CCNP
Whether you're working on your CCNA or CCNP, Cisco certification exams are the most demanding computer certification exams in the IT field. Cisco exams are not a test of memorization, they're a test of your analytical skills. You'll need to look at configurations and console output and analyze them to identify problems and answer detailed questions. To pass these demanding exams, you've got to truly understand how Cisco routers and switches operate - and the key to doing so is right in front of you.

The debug command.

Of course, there is no single "debug" command. Using IOS Help, you can quickly see that there are hundreds of these debugs, and I want to mention immediately that you should never practice these commands on a production router. This is one major reason you need to get some hands-on experience with Cisco products in a home lab or rack rental. No software program or "simulator" is going to give you the debug practice you need.

Now, why am I so insistent that you use debugs? Because that's how you actually see what's going on. It's not enough to type a frame relay LMI command, you have to be able to see the LMIs being exchanged with "debug frame lmi". You don't want to just type a few network numbers in after enabling RIP, you want to see the routes being advertised along with their metrics with "debug ip rip". The list goes on and on.

By using debugs as part of your CCNA and CCNP studies, you're going beyond just memorizing commands and thinking you understand everything that's happening when you enter a command or two. You move to a higher level of understanding how routers, switches, and protocols work -- and that is the true goal of earning your CCNA and CCNP. Stumble Upon Toolbar

Friday, December 26, 2008

Cisco CCNA Certification: Defining Broadcast Domains

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! Stumble Upon Toolbar

Thursday, December 25, 2008

Cisco CCNA Certification Tutorial: Segmenting Your Network

Cisco CCNA Certification Tutorial: Segmenting Your Network
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! Stumble Upon Toolbar

Wednesday, December 24, 2008

Cisco CCNA Exam Tutorial: Route Summarization

Cisco CCNA Exam Tutorial: Route Summarization
Preparing to pass the CCNA exam and earn this important Cisco certification? Route summarization is just one of the many skills you'll have to master in order to earn your CCNA. Whether it's RIP version 2, OSPF, or EIGRP, the CCNA exam will demand that you can flawlessly configure route summarization.

Route summarization isn't just important for the CCNA exam. It's a valuable skill to have in the real world as well. Correctly summarizing routes can lead to smaller routing tables that are still able to route packets accurately - what I like to call "concise and complete" routing tables.

The first skill you've got to have in order to work with route summarization is binary math; more specifically, you must be able to take multiple routes and come up with both a summary route and mask to advertise to downstream routers. Given the networks 100.16.0.0 /16, 100.17.0.0 /16, 100.18.0.0 /16, and 100.19.0.0 /16, could you quickly come up with both the summary address and mask? All you need to do is break the four network numbers down into binary strings. We know the last two octets will all convert to the binary string 00000000, so in this article we'll only illustrate how to convert the first and second octet from decimal to binary.

100 16 = 01100100 00010000

100 17 = 01100100 00010001

100 18 = 01100100 00010010

100 19 = 01100100 00010011

To come up with the summary route, just work from left to right and draw a line where the four networks no longer have a bit in common. For these four networks, that point comes between the 14th and 15th bits. This leaves us with this string: 01100100 000100xx. All you need to do is convert that string back to decimal, which gives us 100 for the first octet and 16 for the second. (The two x values are bits on the right side of the line, which aren't used in calculating the summary route.) Since we know that zero is the value for the last two octets, the resulting summary network number is 100.16.0.0.

But we're not done! We now have to come up with the summary mask to advertise along with the summary route. To arrive at the summary route, write out a mask in binary with a "1" for every bit to the left of the line we drew previously, and a "0" for every bit to the right. That gives us the following string:

11111111 11111100 00000000 00000000

Converting that to dotted decimal, we arrive at the summary mask 255.252.0.0. The correct summary network and mask to advertise are 100.16.0.0 252.0.0.0.

For the CCNA exam, emphasis is put on knowing how to advertise these summary routes in RIPv2 and EIGRP. For both of these protocols, route summarization happens at the interface level - it's not configured under the protocol. On the interface that should advertise the summary route, use the command "ip summary-address". Here are examples of how the above summary route would be configured on ethernet0 in both RIPv2 and EIGRP.

R1(config-if)#ip summary-address rip 100.16.0.0 255.252.0.0

R1(config-if)#ip summary-address eigrp 100 100.16.0.0 255.252.0.0

The main difference between the two is that the EIGRP command must specify the AS number - that's what the "100" is in the middle of the EIGRP command. Since RIPv2 does not use AS numbers, there's no additional value needed in the configuration.

For OSPF, the commands differ. If you're configuring inter-area route summarization, use the "area range" command; if you are summarizing routes that are being redistributed into OSPF, use the summary-address command under the OSPF routing process on the ASBR. Neither of these are interface-level commands.

I speak from experience when I tell you that practice makes perfect on the CCNA exam, especially with binary and summarization questions. The great thing about these questions is that there are no grey areas with these questions - you either know how to do it or you don't. And with practice and an eye for detail, you can master these skills, pass the exam, and become a CCNA. Here's to your success! Stumble Upon Toolbar

Tuesday, December 23, 2008

Cisco/Microsoft Computer Certification: Be Ready For Your Opportunity

Cisco/Microsoft Computer Certification: Be Ready For Your Opportunity
I was reading The Big Moo: Stop Trying To Be Perfect and Start Being Remarkable this morning, and I’d recommend a copy of this to anyone who wants to improve their career and their future. And that’s all of us, right?

There was one particular line that really stood out to me: Betting on change is always the safest bet available. That describes life perfectly, but it also describes a career in Information Technology perfectly as well. There is no field in the world that has the constant and never-ending changes that IT does. And every single one of us can look at this as a massive opportunity for personal and professional growth.

Is that how you’re looking at it? I remember when I passed my first certification exam, the Novell CAN, back in 1997. Man, I thought I knew it all then! But I quickly learned that you’ve got to keep learning in IT. I also learned that if you’re willing to put in the work and make the sacrifices, there’s no other field with the limitless potential for growth and excellence.

Like everyone else, my career has had its ups and downs, but I always kept learning and growing. Today, I’ve got my dream job, working with students and customers just like you – to help you create your own future.

The next 18 months are filled with endless possibilities, particularly with the rapid growth of VoIP and Microsoft Vista on the horizon. There will be those who rationalize their inertia, saying “I’ll never have to support those, so I don’t need to learn them."

There will also be those who see VoIP and Vista as enormous opportunities to learn and advance in their careers and their lives. These people will get started today, learning the fundamentals of Cisco and advancing their networking knowledge in order to be ready for opportunities as they come along.

You can’t start studying and learning when the opportunity arrives – you’ve got to be ready when opportunity knocks. If you’ve been putting off studying for a Cisco or other computer certification – and I know the summer is a really good time for putting off studying – get back on track today.

Because you never know what opportunities are going to come along – but you do know that when they do, you’ve got to be ready to take advantage. After all, opportunity really does knock only once! Stumble Upon Toolbar

Cisco CCNA Exam Tutorial: Loopback Interfaces

Cisco CCNA Exam Tutorial: Loopback Interfaces
As a CCNA candidate, you most likely have some background in PC hardware and workstation support. If so, you're already familiar with loopback interfaces, particularly 127.0.0.1, the loopback address assigned to a PC.

When you're learning all about the different physical interfaces for your CCNA exam - serial, ethernet, and BRI, among others - there's one logical interface you need to know about, and that is - you guessed it! - the loopback interface.

What isn't as immediately apparent is why we use loopback interfaces on routers and switches to begin with. Many of the Cisco router features that can use loopbacks are intermediate and advanced features that you'll learn about in your CCNP and CCIE studies, but these features all come back to one basic concept: If the loopback interface on a router is down, that means the router is unavailable as a whole.

In contrast, a physical interface being down does not mean the router itself is out of commission. A router's ethernet port can go down, but the other physical interfaces on that router are still operational. Since a loopback interface is logical, there's nothing physical that can go wrong with it.

As I mentioned, you'll learn different Cisco router and switch features that utilize loopback interfaces as you climb the Cisco certification ladder. There's one misconception about Cisco loopback interfaces that you want to get clear on now, though. You’re probably familiar with loopback interfaces on a PC, and may even know that the address range 127.0.0.0 is reserved for loopback addressing.

Note that this reserved address range does not apply to loopbacks on Cisco devices, however. If you attempt to assign an address from this range to a Cisco loopback interface, you get this result:

R1#conf t

Enter configuration commands, one per line. End with CNTL/Z.

R1(config)#interface loopback0

R1(config-if)#ip address 127.0.0.2 255.255.255.0

Not a valid host address - 127.0.0.2

R1(config-if)#ip address 127.1.1.1 255.255.255.0

Not a valid host address - 127.1.1.1

The range 127.0.0.0 is reserved for host loopbacks (such as PCs), not routers or switches. The most commonly used address from this range is 127.0.0.1 – if you can’t ping that on a workstation, that means you can’t ping yourself, which means there’s a problem with the TCP/IP install itself.

Keep these details in mind on the exam and in the workplace, and you’re on your way to CCNA exam success! Stumble Upon Toolbar

Monday, December 22, 2008

Cisco Business VoIP – an Answer to Unified Communication

Cisco Business VoIP – an Answer to Unified Communication
The advent of technology never stops. There is this never-ending quest for perfection and change. Every sector is constantly changing due to the advances in the technology so that it offers something new to the general public and will keep abreast of the developing times and people. Like any other industry, the advent of technology has changed the way film-making and video gaming has evolved.

Lot of changes has happened over a period of time in the way films are made. With the modern methods employed by film makers of current times, movies of today have evolved in a way to generate more viewing pleasure to the public. Lots of options like science fiction, fantasy and animation are now available thanks to technology. The same goes to the gaming industry. In the beginning, we had only the 2D graphics and the boring audio of gaming consoles like Magnavox and Atari while we are now seeing seventh generation gaming consoles like the Xbox 360 and PlayStation 3 that are really captured the world by storm.

Technology has altered the outlook of People

As with any other sector, communication has also developed with the changing face of technology. Earlier means of communication was restricted to using Morse code and telegraph. Now, we have evolved means of communication that has served in bringing people all over the world together and has really made the Earth a smaller place.

The initiation of the world of communication began with the telephone. This mode of communication allowed people to talk to other people anywhere in the world in real time and were charged for the call on a minute basis or a flat rate of the entire call based on the mode followed by the service provider. Then came the mobile phones which further revolutionized the communication sector by allowing people to talk to one another even while on the move and even when the person was in any isolated part of the world provided that the service provider had network coverage in that area. So, technology has really made communication an easy and convenient resource for one and all.

The growth in communication sector has not been restricted to these devices. The beginning of the 21st century saw the entry of another powerful communication tool that has not only improved communication means it has also reduced costs to the consumer. This tool is the Voice over Internet Protocol or VoIP. This new tool has become quite popular in the short while that it has existed and is still growing.

VoIP is a very efficient tool in providing for better communication. It differs from the conventional telephone in that it does not rely on cables nor does it use signal towers like the mobile phone. VoIP uses the internet to allow person to handle calls. So, VoIP as the name suggests sends voice through the Internet or an Internet Protocol (IP) based network.

The popularity of VoIP boomed suddenly and is still growing because of the low cost rates it offers in terms of the setup and the regular bills every month. The basic requirement is only one VoIP infrastructure that can be further modified if more lines are needed later. The operational costs of VoIP are around 22% lesser than what is required by circuit switched networks. For this reason, the setup costs and the bills incurred by a consumer monthly is much cheaper while using VoIP in comparison to a conventional telephone.

These qualities have pressurized many telecommunication majors to move over to the VoIP system. One such organization is Cisco that offers VoIP systems to businesses to help them incorporate a common platform for their communication needs and their business processes and also to ascertain the safety of data which is sent across through this system.

The initial VoIP system provided by Cisco known as Cisco Unified Communication has become a popular communication tool not only for voice but also to send data. It provides a wonderful blend of networking safety and open application programming interface to create a proficient channel for all business communication and has made network management much easier and reduced the operational costs to the organizations.

Cisco now plans to provide a VoIP system meant to serve the needs of every common man. With this new step, they will be entering a realm of providing cost effective and a great communication tool to the entire world. Stumble Upon Toolbar

CISCO Certification: An Introduction To Multilayer Switching And SVIs

CISCO Certification: An Introduction To Multilayer Switching And SVIs
Sure, you have to know all about SVIs and multilayer switching to earn your CCNP, but you also need to know about them because they’re so commonplace in today’s networks!

Why? We can use an SVI to allow inter-VLAN communication on a multilayer switch, eliminating the need for a separate router to get involved.

In this example, we have Host_1 in VLAN 11 and Host_3 in VLAN 33. Before we begin configuring, we'll send pings between the two hosts. (We’ll use Cisco routers for the hosts in this lab, which is why the ping output may look familiar!)

HOST_1#ping 30.1.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 30.1.1.1, timeout is 2 seconds:.....

Success rate is 0 percent (0/5)

HOST_3#ping 20.1.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 20.1.1.1, timeout is 2 seconds:

.....

Success rate is 0 percent (0/5)

As we expect, there’s no IP connectivity between the hosts. Assuming the appropriate switch ports are already placed in VLAN 11 and VLAN 33, we’ll now create two switched virtual interfaces on this multilayer switch. One will represent VLAN 33, and the other will represent VLAN 11.

SW1(config)#int vlan11

01:30:04: %LINK-3-UPDOWN: Interface Vlan11, changed state to up

01:30:05: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan11, changed state to up

SW1(config-if)#ip address 20.1.1.11 255.255.255.0

SW1(config-if)#int vlan33

01:30:11: %LINK-3-UPDOWN: Interface Vlan33, changed state to up

01:30:12: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan33, changed state to up

SW1(config-if)#ip address 30.1.1.11 255.255.255.0

At this point, we’ve still got a problem when we look at the routing table.

SW1# show ip route

Default gateway is not set

Host Gateway Last Use Total Uses Interface

ICMP redirect cache is empty

The problem is that we don’t have a routing table, because IP routing is off by default on a multilayer switch. Let’s turn IP routing on and then check the routing table.

SW1(config)#ip routing

SW1(config)#^Z

SW1#show ip route

Gateway of last resort is not set

20.0.0.0/24 is subnetted, 1 subnets

C 20.1.1.0 is directly connected, Vlan11

30.0.0.0/24 is subnetted, 1 subnets

C 30.1.1.0 is directly connected, Vlan33

Now we’re in good shape! The hosts need to have their default gateway set to the appropriate SVI IP address; here, Host_1 should have its gateway set to 20.1.1.11, and Host_3 to 30.1.1.11. After doing so, inter-VLAN communication is now in place, as shown by the ping output below.

HOST_1#ping 30.1.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 30.1.1.1, timeout is 2 seconds: !!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/4 ms

HOST_3#ping 20.1.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 20.1.1.1, timeout is 2 seconds: !!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms

In a future Cisco certification tutorial, we’ll take a look at configuring a multilayer switch port as a routed port, and assign an IP address to that port. See you then! Stumble Upon Toolbar

Sunday, December 21, 2008

Cisco CCNP Certification: Using The BGP Command “Update-Source”

Cisco CCNP Certification: Using The BGP Command “Update-Source”
When you start preparing for your CCNP exam, particularly the BSCI exam, you're introduced to Border Gateway Protocol (BGP) configurations. BGP is unlike any protocol you learned during your CCNA studies, and even the similarities are a little bit different!

BGP forms neighbor relationships, much like EIGRP and OSPF do. The interesting thing with BGP is that potential neighbors, or "peers", do not need to be directly connected and can use their loopback interfaces to form the peer relationships.

It may well be to your advantage to use loopbacks to form peer relationships rather than the actual interface facing the potential neighbor. This can be done because BGP uses static neighbor statements rather than any kind of dynamic neighbor discovery process.

Consider a router that has two paths to a BGP speaker. The interfaces are numbered like this:

Router1: Serial0, 172.1.1.1 /24, Serial2, 179.1.1.1 /24, loopback0, 1.1.1.1 /32.

Router2: Serial0, 172.1.1.2/24, Serial2 179.1.1.2/24, loopback0, 2.2.2.2 /32.

We could configure Router1 like this:

router bgp 200

neighbor 172.1.1.2 remote-as 200

In this case, BGP would automatically use 172.1.1.1 as the source for the TCP connection that has to be set up with the neighbor before updates can be exchanged; this address is known as the best local address. However, if the remote peer's serial0 interface is shut down or goes down for another reason, the peer relationship would be lost even though Router2 is still available.

Instead of using one of the physical interfaces, we can use the loopbacks on each router to establish the TCP-based peer connection. The configurations would look like this:

Router1:

router bgp 200

neighbor 2.2.2.2 remote-as 200

neighbor 2.2.2.2 update-source loopback0

Router2:

router bgp 200

neighbor 1.1.1.1 remote-as 200

neighbor 1.1.1.1 update-source loopback0

In this case, losing one of the physical connections does not necessarily mean the BGP peering is lost; as long as the routers have a valid path to each other's loopback addresses, the BGP peer relationship will stay in place. And better yet, we avoid the dreaded “single point of failure”! Stumble Upon Toolbar

Cisco CCNA/CCNP Home Lab: Why You Need An ISDN Simulator

Cisco CCNA/CCNP Home Lab: Why You Need An ISDN Simulator
ISDN is a vital topic for today's CCNA and CCNP candidates, especially for the ICND and Intro exams - you've got to know ISDN inside and out to pass those exams. Naturally you want to include it in your home lab. What many candidates don't realize is that you can't connect two Cisco routers directly via their Basic Rate Interface (BRI) interfaces you've got to have another device between them called an ISDN simulator.

An ISDN simulator is not one of those software programs pretending to be routers ("router simulators") this is a piece of hardware that acts as the telephone company in your home lab. Older simulators come with preprogrammed phone numbers and SPIDs, where newer ones let you program the phone numbers you want to use. Either way, an ISDN simulator is great for your CCNA/CCNP home lab, because you can practice dial scenarios that actually work. And you get to troubleshoot the ones that don't, which is also important to learn!)

You don't need any special cables or connectors you just connect both of your routers' BRI interfaces to the ISDN simulator with a straight-through cable and you're ready to go.

In years past, this was a major problem for 640-801, 811, and 821 studies, because the simulators used to be so expensive. New ones can still be pricey ($600 and up), but with the sudden influx of used ISDN simulators on ebay and Cisco resellers, you can get a used one that will do the job for you.

Why are there suddenly so many ISDN simulators on the market? Cisco recently removed ISDN from the CCIE R&S exam, so a lot of CCIE rack resellers as well as private individuals are selling their simulators. There's never been a better time to add ISDN to your home lab. If taken care of (kept out of extreme heat), they can last for quite a few years. The one I purchased for my IE home lab is still working well.

If you choose to purchase a new simulator, you can run a Google search to find vendors. I've made two purchases from www.vconsole.com over the last few years and both of those simulators have worked beautifully.

As I said earlier, there's never been a better time to add ISDN to your home lab. Don't just settle for trying to memorize theory - get your hands on the real deal, practice and fix your configurations, and you'll be amazed at what you learn and how well you do on your CCNA and CCNP exams! Stumble Upon Toolbar

Saturday, December 20, 2008

Cisco CCNP Certification: BGP Attribute Category Tutorial

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! Stumble Upon Toolbar

Cisco CCNA/CCNP Certification: Introduction To BGP Attributes

Cisco CCNA/CCNP Certification: Introduction To BGP Attributes
BGP is one of the most complex topics you'll study when pursuing your CCNP, if not the most complex. I know from personal experience that when I was earning my CCNP, BGP is the topic that gave me the most trouble at first. One thing I keep reminding today's CCNP candidates about, though, is that no Cisco technology is impossible to understand if you just break it down and understand the basics before you start trying to understand the more complex configurations.

BGP attributes are one such topic. You've got well-known mandatory, well-known discretionary, transitive, and non-transitive. Then you've got each individual BGP attribute to remember, and the order in which BGP considers attributes, and what attributes even are... and a lot more! As with any other Cisco topic, we have to walk before we can run. Let's take a look at what attributes are and what they do in BGP.

BGP attributes are much like what metrics are to OSPF, RIP, IGRP, and EIGRP. You won't see them listed in a routing table, but attributes are what BGP considers when choosing the best path to a destination when multiple valid (loop-free) paths exist.

When BGP has to decide between such paths, there is an order in which BGP considers the path attributes. For success on the CCNP exams, you need to know this order. BGP looks at path attributes in this order:

Highest weight (Cisco-proprietary BGP value)

Highest local preference (LOCAL_PREF)

Prefer locally originated route.

Shortest AS_PATH is preferred.

Choose route with lowest origin code. Internal paths are preferred over external paths, and external paths are preferred over paths with an origin of "incomplete".
Lowest multi-exit discriminator (MED)

External BGP routes preferred over Internal BGP routes.

If no external route, select path with lowest IGP cost to the next-hop router for iBGP.

Choose most recent route.

Choose lowest BGP RID (Router ID).

If you don't know what these values are, or how they're configured, don't panic! The next several parts of this BGP tutorial will explain it all. So spend some time studying this order, and in part II of this free BGP tutorial, we'll look at each of these values in detail. Keep studying! Stumble Upon Toolbar

Friday, December 19, 2008

Cisco CCNP / BSCI Tutorial: The BGP Attribute Next_hop

Cisco CCNP / BSCI Tutorial: The BGP Attribute Next_hop
When you're studying for the BSCI exam on the way to earning your CCNP certification, you've got to master the use of BGP attributes. These attributes allow you to manipulate the path or paths that BGP will use to reach a given destination when multiple paths to that destination exist.

In this free BGP tutorial, we're going to take a look at the NEXT_HOP attribute. You may be thinking "hey, how complicated can this attribute be?" It's not very complicated at all, but this being Cisco, there's got to be at least one unusual detail about it, right?

The NEXT_HOP attribute is simple enough - this attribute indicates the next-hop IP address that should be taken to reach a destination. In the following example, R1 is a hub router and R2 and R3 are spokes. All three routers are in BGP AS 100, with R1 having a peer relationship with both R2 and R3. There is no BGP peering between R2 and R3.

R3 is advertising the network 33.3.0.0 /24 via BGP, and the value of the next-hop attribute on R1 is the IP address on R3 that is used in the peer relationship, 172.12.123.3.

The issue with the next-hop attribute comes in when the route is advertised to BGP peers. If R3 were in a separate AS from R1 and R2, R1 would then advertise the route to R2 with the next-hop attribute set to 172.12.123.3. When a BGP speaker advertises a route to iBGP peers that was originally learned from an eBGP peer, the next-hop value is retained.

Here, all three routers are in AS 100. What will the next-hop attribute be set to when R1 advertises the route to its iBGP neighbor R2?

R2#show ip bgp

< no output >

There will be no next-hop attribute for the route on R2, because the route will not appear on R2. By default, a BGP speaker will not advertise a route to iBGP neighbors if the route was first learned from another iBGP neighbor.

Luckily for us, there are several ways around this rule. The most common is the use of route reflectors, and we'll look at RRs in a future free BGP tutorial. Stumble Upon Toolbar

Cisco CCNP/BSCI Certification: Introduction To ISIS Terminology

Cisco CCNP/BSCI Certification: Introduction To ISIS Terminology
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! Stumble Upon Toolbar

Thursday, December 18, 2008

Cisco CCNA / CCNP Certification: Deciphering Ping Results

Cisco CCNA / CCNP Certification: Deciphering Ping Results
As you study for your CCNA and CCNP exams, particularly if you're getting hands-on practice in your home lab or rack rental service, you're going to be sending a lot of pings. As a CCNA or CCNP candidate, you know that five exclamation points (!!!!!) as a ping return indicates that you have IP connectivity to the remote destination. Five periods (.....) indicates that you do not have that connectivity.

It's not enough to know that you don't have IP connectivity to the remote device, you've got to know why. Ping is a great first step to network troubleshooting, but the results are quite limited. As a CCNA and CCNP, you've got to know how to diagnose the problem and resolve it. Just looking at the routing table is not enough - a high-powered Cisco debug, debug ip packet, can often show you exactly where the problem is.

WARNING: debug ip packet should not be run on any production router without understanding the effect of this command on your router. This command results in a lot of output and can actually lock up a router.

In this case, we'll run the command on a home lab router that cannot ping 22.2.2.2. The debug will be turned on and another ping sent.

R1#debug ip packet

IP packet debugging is on

R1#ping 22.2.2.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 22.2.2.2, timeout is 2 seconds:

3d23h: IP: s=1.1.1.1 (local), d=22.2.2.2, len 100, unroutable.

R1#undebug all

All possible debugging has been turned off

I've edited this output for clarity; the important word is "unroutable". This indicates that the packet is not leaving the router because there is no match in the routing table for this destination. We'll configure a static default route and send the ping again.

R1#ping 22.2.2.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 22.2.2.2, timeout is 2 seconds:

U.U.U

Success rate is 0 percent (0/5)

That output may surprise those of you who are used to getting five of the same symbol back whenever you send a ping. We got three "U"s back along with two periods. We'll now run debug ip packet and send the ping again.

R1#debug ip packet

IP packet debugging is on

R1#ping 22.2.2.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 22.2.2.2, timeout is 2 seconds:

3d23h: IP: s=172.12.123.1 (local), d=22.2.2.2 (Serial0), len 100, sending

R1#traceroute 22.2.2.2

Type escape sequence to abort.

Tracing the route to 22.2.2.2

1 172.12.123.2 36 msec 36 msec 36 msec

2 172.12.123.2 !H * !H

R1#undebug all

All possible debugging has been turned off

Again, I've edited this output. The key word in this output is "sending", meaning that the packets are leaving the router. The ping return of "U.U.U" is a general indication that the packets are indeed being transmitted, but that a downstream router is having a problem routing the packets. Running traceroute reveals some more interesting return characters! In this case, the downstream router did not have a match for the destination in its routing table.

It's easy to concentrate on the local router when you're not getting positive ping returns. When troubleshooting this kind of issue, keep in mind the problem could be on an intermediate router and not on the local router. Use debug ip packet to make sure the packets are leaving the local router, and traceroute to determine what downstream router may have the problem. And get used to the fact that pings and traceroutes can give you some unusual-looking returns! Stumble Upon Toolbar

Cisco CCNA / CCNP Home Lab Tutorial: Starting Over

Cisco CCNA / CCNP Home Lab Tutorial: Starting Over
When you're preparing for success on your CCNA or CCNP certification exams, sooner or later you're going to want to start totally from scratch on your Cisco routers and switches. It's easy enough to type "write erase" and "reload", but there are a few details you have to watch if you want your home lab or rack rental devices to act as though they just came out of the box.

The first step is indeed to run the command write erase, and then reload the router. You're going to be prompted with a question before the reload starts, though, and you have to give the right answer .... or your configuration will still be there when you reload!

First, you will be prompted to confirm the erase. Press to accept the default answer of "confirm".

R1#write erase

Erasing the nvram filesystem will remove all configuration files! Continue? [confirm]

[OK]

Erase of nvram: complete

With the startup configuration erased, it's time to reload the router. This is where the second prompt comes in:

R1#reload

System configuration has been modified. Save? [yes/no]: no

When a Cisco router prompts you with two answers to a question, you've got to type the answer in (or at least the first letter of it). Answer NO to this question and press when prompted to confirm the reload.

The router will then start the reload process. Since there is no startup configuration in NVRAM, the router will prompt you to enter setup mode. You should only answer yes if you have a lot of time on your hands, just want to see what setup mode is like, or practice CTRL-C to get out it! Otherwise, answer NO.

--- System Configuration Dialog ---

Would you like to enter the initial configuration dialog? [yes/no]: n

Would you like to terminate autoinstall? [yes]:y

You'll see quite a few messages after this relating to interface states, and finally you're back at the user exec prompt.

Router>

Now you're working with a router that's just like it was when it came out of the box!

For switches such as the 2950, the process is much the same, but you should delete the VLAN.DAT file before reloading the router. This file contains VLAN information and is kept in flash, so it will still be present after a reload.

switch1#write erase

Erasing the nvram filesystem will remove all files! Continue? [confirm]

[OK]

Erase of nvram: complete

switch1#delete vlan.dat

Delete filename [vlan.dat]?

Delete flash:vlan.dat? [confirm]

switch1#reload

Make sure to hit for the two questions regarding the deletion - if you answer "y" instead, the switch thinks you're trying to erase a file named "y"!

After the reload is complete, you'll be prompted to enter setup mode. As you did with the router, enter "N" and begin to configure the router from user exec mode. There's nothing like working with real equipment to prepare for your CCNA and CCNP success, and there's no better practice than configuring routers and switches from the very beginning! Stumble Upon Toolbar

Wednesday, December 17, 2008

Cisco CCNA Certification: Defining And Creating Collision Domains

Cisco CCNA Certification: Defining And Creating Collision 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 "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! Stumble Upon Toolbar

Cisco CCNP / BSCI Tutorial: The Role Of The OSPF ASBR

Cisco CCNP / BSCI Tutorial: The Role Of The OSPF ASBR
To pass the BSCI exam and earn your CCNP certification, you've got to master the (many) details of OSPF. You might have thought there were quite a few OSPF details in your CCNA studies, but you'll now build on that foundation on the way to earning your CCNP.

One such detail is the role of the Autonomous System Border Router (ASBR) in OSPF. The name itself raises some eyebrows, since you learned in your CCNA studies that OSPF doesn't use autonomous systems! Just as an OSPF Area Border Router borders multiple OSPF areas, the ASBR borders the entire OSPF domain and another source of routes. This can be another dynamic routing protocol, or directly connected networks that are not being advertised into OSPF by the network command.

Let's say we have a router running both OSPF and RIP version 2. By default, the RIP process will not contain any OSPF-discovered routes, and vice versa. The two separate routing processes are just that - separate. If we want the other OSPF routers to know about the RIP routes, route redistribution must be configured. When the RIP routes are redistributed into OSPF, that router is then an ASBR.

In the below example, RIP subnets have been redistributed into OSPF. A seed metric is not necessary when redistributing routes into OSPF. The command "show ip ospf" confirms that this router is now an ASBR.

R1(config)#router ospf 1

R1(config-router)#redistribute rip subnets

R1#show ip ospf

Routing Process "ospf 1" with ID 1.1.1.1

Supports only single TOS(TOS0) routes

Supports opaque LSA

It is an autonomous system boundary router

The ASBR can also perform route summarization on the routes being injected into OSPF with the summary-address command. (To configure OSPF inter-area summarization, use the area range command.) By mastering route summarization and route redistribution, you're well on your way to passing the BSCI exam and earning your CCNP certification! Stumble Upon Toolbar

Tuesday, December 16, 2008

Cisco CCNP/BSCI Exam Tutorial: IP Version 6 Zero Compression

Cisco CCNP/BSCI Exam Tutorial: IP Version 6 Zero Compression
BSCI exam success is all part of becoming a CCNP, and part of that success is now learning the basics of IP Version 6, or IPv6. One of the most difficult parts of learning IPv6 concepts is the radically different addressing scheme that IPv6 uses as compared to IPv4. Just look at these sample addresses:

Typical IPv4 address: 129.14.12.200

Typical IPv6 address: 1029:9183:81AE:0000:0000:0AC1:2143:019B

As you can see, IPv6 isn't exactly just tacking two more octets onto an IPv4 address!

I haven't met too many networkers who really like typing, particularly numbers. You'll be happy to know there are some rules that will shorten those addresses a bit, and it's a very good idea to be fluent with these rules for your exam.

You remember from your CCNA studies that there's no difference between an upper-case letter and lower-case letter in hexadecimal. That's one of three basic rules you need to know when working with IPv6 addressing. The other factors deal with all the zeroes you'll run into in IPv6 addresses! One of these rules is the rule of zero compression.

The rule of zero compression states that if an address contains consecutive fields of zeroes, they can be expressed with two colons. It doesn't matter if you have two fields or eight, you can simply type two colons and that will represent all of them. The key here is that you can only do this once in an IPv6 address. This is referred to as zero compression. Here's an example:

Original format: 1234:1234:0000:0000:0000:0000:3456:3434

Using zero compression: 1234:1234::3456:3434

Again, you must remember that you can only do this once in an IPv6 address expression.

What if there are zeroes in the address that don't quite fit this rule? The next part of our IPv6 tutorial will deal with leading zero compression, another tool you can use to shorten these long, long addresses! Stumble Upon Toolbar

Cisco CCNA Certification Exam Tutorial: Prefix Notation

Cisco CCNA Certification Exam Tutorial: Prefix Notation
When you're preparing to pass the CCNA exam and earn this coveted Cisco certification, you've got to be totally prepared for the many kinds of binary and subnetting questions Cisco may throw at you. You also have to be familiar with the different manners in which a subnet mask can be expressed, and that’s where your knowledge of prefix notation comes in. Prefix notation is an alternate way to express the value of a subnet mask, as opposed to the more familiar dotted decimal format. Not only will you see prefix notation in Cisco documentation, but you’ll probably see it on your CCNA exam. Consider the following two values:

255.255.255.0

/24

Believe it or not, those two values are exactly the same. The first mask is written out in the more familiar dotted decimal format, and you know by looking at those first three octets that every bit is set to "1", since the maximum value of such an octet is 255.

The second value represents the exact same mask, only this value is expressed in prefix notation. This particular value would be pronounced "slash twenty-four", and the 24 represents the number of consecutive ones that are set in the subnet mask.

Those of us who hate to type numbers are particularly appreciative of this, since it means you'll have to type a lot less numbers to represent a subnet mask. In addition, it's a lot easier to discuss masks in prefix notation than dotted decimal. ("I thought about using a two-fifty-five two-fifty-five two-fifty-five zero mask ,but then decided to use a two-fifty-five two-fifty-five two-fifty-five one-twenty-eight mask...")

Be sure you're comfortable with prefix notation before taking your CCNA exam. As with Cisco documentation, you'll most likely see masks expressed in both dotted decimal and prefix notation, and you've got to be ready to use the both as well! Stumble Upon Toolbar

Monday, December 15, 2008

Cisco CCNP/BCMSN Exam Tutorial: Static VLANs

Cisco CCNP/BCMSN Exam Tutorial: Static VLANs
BCMSN exam success and earning your CCNP certification requires you to add to your knowledge of VLAN configuration. When you studied for your CCNA exam, you learned how to place ports into a VLAN and what the purpose of VLANs was, but you may not be aware that there are two types of VLAN membership. To pass the BCMSN exam, you must know the details of both types.

In this tutorial, we'll take a look at the VLAN type you are most familiar with, the "static VLAN". As you know, VLANs are a great way to create smaller broadcast domains in your network. Host devices connected to a port belonging to one VLAN will receive broadcasts and multicasts only if they were originated by another host in that same VLAN. The drawback is that without the help of a Layer 3 switch or a router, inter-VLAN communication cannot occur.

The actual configuration of a static VLAN is simple enough. In this example, by placing switch ports 0/1 and 0/2 into VLAN 12, the only broadcasts and multicasts hosts connected to those ports will receive are the ones transmitted by ports in VLAN 12.

SW1(config)#int fast 0/1

SW1(config-if)#switchport mode access

SW1(config-if)#switchport access vlan 12

% Access VLAN does not exist. Creating vlan 12

SW1(config-if)#int fast 0/2

SW1(config-if)#switchport mode access

SW1(config-if)#switchport access vlan 12

One of the many things I love about Cisco switches and routers is that if you have forgotten to do something, the Cisco device is generally going to remind you or in this case actually do it for you. I placed port 0/1 into a VLAN that did not yet exist, so the switch created it for me!

There are two commands needed to place a port into a VLAN. By default, these ports are running in dynamic desirable trunking mode, meaning that the port is actively attempting to form a trunk with a remote switch in order to send traffic between the two switches. The problem is that a trunk port belongs to all VLANs by default, and we want to put this port into a single VLAN only. To do so, we run the switchport mode access command to make the port an access port, and access ports belong to one and only one VLAN. After doing that, we placed the port into VLAN 12 with the switchport access vlan 12 command. Running the switchport mode access command effectively turns trunking off on that port.

The hosts are unaware of VLANs; they simply assume the VLAN membership of the port they're connected to. But that's not quite the case with dynamic VLANs, which we'll examine in the next part of this BCMSN tutorial. Stumble Upon Toolbar

Cisco CCNP/BSCI Exam Tutorial: Leading Zero Compression

Cisco CCNP/BSCI Exam Tutorial: Leading Zero Compression
The BSCI exam and CCNP certification requires that you be well versed in the basics of IP Version 6, or IPv6. If you're new to IPv6, you'll quickly learn that it's not exactly just two more octets slapped onto an IPv4 address! IPv6 addresses are quite long, but there are two ways to acceptably shorten IPv6 address expression. To pass the BSCI exam, become a CCNP, and get that all-important understanding of IPv6, you've got to understand these different methods of expressing an IPv6 address. My last IPv6 tutorial discussed zero compression; today we'll take a look at leading zero compression.

Leading zero compression allows us to drop the leading zeroes from every field in the address. Where we could only use zero compression once in an IPv6 address expression, leading zero compression can be used as often as is appropriate. The key with leading zero compression is that there must be at least one number left in each field, even if that remaining number is a zero.

You sometimes see books or websites refer to leading zero compression as "dropping zeroes and replacing them with a colon", but that explanation can be a little confusing, since the blocks are separated with a colon to begin with. You're not really replacing the leading zeroes, you're dropping them.

Let's look at an example of leading zero compression. Taking the address 1234:0000:1234:0000:1234:0000:1234:0123, we have four different fields that have leading zeroes. The address could be written out as it is, or drop the leading zeroes.

Original format: 1234:0000:1234:0000:1234:0000:0123:1234

With leading zero compression: 1234:0:1234:0:1234:0:123:1234

There's no problem with using zero compression and leading zero compression in the same address, as shown here:

Original format: 1111:0000:0000:1234:0011:0022:0033:0044

With zero and leading zero compression: 1111::1234:11:22:33:44

Zero compression uses the double-colon to replace the second and third block of numbers, which were all zeroes; leading zero compression replaced the "00" at the beginning of each of the last four blocks. Just be careful and take your time with both zero compression and leading zero compression and you'll do well on the exam and in the real world. The keys to success here are remembering that you can only use zero compression once in a single address, and that while leading zero compression can be used as often as needed, at least one number must remain in each field, even if that number is a zero. Stumble Upon Toolbar

Sunday, December 14, 2008

Cisco CCNP Exam Tutorial: Defining Collision Domains

Cisco CCNP Exam Tutorial: Defining Collision Domains
CCNA exam success depends on mastering the fundamentals, and two important fundamentals are knowing exactly what the terms "collision domain" and "broadcast domain" mean. In this free Cisco tutorial, we'll take a look at the term "collision domain" and how a collision domain is defined.

A collision domain is an area in which a collision can occur. Fair enough, but what "collision" are we talking about here? We're talking about collisions that occur on CSMA/CD segments, or Carrier Sense Multiple Access with Collision Detection. If two hosts on an Ethernet segment transmit data at exactly the same time, the data from the two hosts will collide on the shared segment. CSMA/CD exists to lessen the chances of this happening, but collisions can still occur. To lessen the chances of collisions occurring, we may decide to create multiple, smaller collision domains.

Let's say we have four hosts on a single Ethernet segment. The entire segment is a collision domain; any data sent by one of the hosts can collide with data sent by any of the other hosts. We have one collision domain containing four devices.

To create smaller collision domains, we'll need to introduce some type of networking device into this example. Hubs and repeaters have their place as far as extending the reach of a network segment and cutting down on attenuation, but these OSI Layer One devices do nothing to define collision domains. We could connect each host into a separate port on a hub (a hub is basically a multiport repeater) and we'd still have one single collision domain with four hosts in it.

The most common and most effective way to create multiple collision domains is to use a switch. If we connect each of these four hosts to their own separate switch port, we would now have four separate collision domains, each with one host; each switch port actually acts as a single collision domain, making collisions between these four hosts impossible.

Passing the CCNA is all about knowing the details of how things work, and knowing CSMA/CD theory and how to define collision domains is one of the many details you've got to master. In the next part of this CCNA tutorial, we'll take a look at broadcast domains, and how defining broadcast domains in the right places can dramatically cut down on unnecessary traffic on your network. Stumble Upon Toolbar

Cisco CCNP/BSCI Exam Tutorial: Using Distribute Lists

Cisco CCNP/BSCI Exam Tutorial: Using Distribute Lists
To be successful on the BSCI exam and in earning your CCNP, you've got to master route redistribution. This isn't as easy as it sounds, because configuring route redistribution is only half the battle. Whether it's on an exam or in a real-world production network, you've got to identify possible points of trouble before you configure route redistribution - and you need to be able to control redistribution as well. You may have an OSPF domain with 100 routes, but only need to redistribute 10 of them into a neighboring RIPv2 domain. You've got to know how to do that, and one method is the use of a distribute-list.

A distribute-list is an access-list that is used to determine what routes can and cannot be redistributed. Distribute-lists let you specify what routes will be filtered from the process. You can use standard or extended ACLs, and you can filter routes that are coming into a routing process or being injected into another process.

In the following example, R1 is redistributing RIP routes into OSPF, but only wants to advertise network 150.1.1.0 /24 to other OSPF routers. An ACL will be written to match that particular network, and then the distribute-list will be written under the routing process. I'm going to show you the IOS Help output for the distribute-list command, and please note that routing updates can be controlled at the interface level or protocol level.

R1(config)#access-list 24 permit 150.1.1.0 0.0.0.255

R1(config)#router ospf 1

R1(config-router)#redistribute rip subnets

R1(config-router)#distribute-list 24 ?

in Filter incoming routing updates

out Filter outgoing routing updates

R1(config-router)#distribute-list 11 out ?

Async Async interface

BRI ISDN Basic Rate Interface

BVI Bridge-Group Virtual Interface

CTunnel CTunnel interface

Dialer Dialer interface

Ethernet IEEE 802.3

Lex Lex interface

Loopback Loopback interface

Multilink Multilink-group interface

Null Null interface

Serial Serial

Tunnel Tunnel interface

Vif PGM Multicast Host interface

Virtual-Template Virtual Template interface

Virtual-TokenRing Virtual TokenRing

bgp Border Gateway Protocol (BGP)

connected Connected

egp Exterior Gateway Protocol (EGP)

eigrp Enhanced Interior Gateway Routing Protocol (EIGRP)

igrp Interior Gateway Routing Protocol (IGRP)

ospf Open Shortest Path First (OSPF)

rip Routing Information Protocol (RIP)

static Static routes

R1(config-router)#distribute-list 11 out rip

Using distribute-lists does guard against routing loops, but they have other purposes. You may have a network segment that should be kept secret from the rest of your company; a distribute-list can filter that segment's network number from the redistribution process. In this way, distribute-lists serve as a basic form of network security. (Very basic. I wouldn't sell that firewall on ebay if I were you.)

Keeping such networks out of routing updates and routing tables throughout the network has the side effect of reducing routing update overhead as well. Stumble Upon Toolbar

Cisco CCNA Exam Tutorial: Five ISDN Details To Remember

Cisco CCNA Exam Tutorial: Five ISDN Details To Remember
CCNA exam success depends on mastering many technologies that are new to you, and few exam topics have more details than ISDN. ISDN isn't just for your CCNA exam studies, though. While ISDN is dismissed by many, the fact is that there are many small and mid-size networks out there that use ISDN as their backup to frame relay. Some of these companies have spoke networks that use ISDN to connect to their hub as well, so it's a great idea to know ISDN configuration and troubleshooting for your real-world career as well as passing the CCNA. With that in mind, let's take a look at five common ISDN errors and how to avoid them.

With dialer map statements, remember that the phone number you put in the dialer map is the phone number of the remote router, not the local one. Look at it this way - if you want to call a friend on your cell, you don't pick up your cell and dial your own number!

Speaking of dialer map statements, don't forget the all-important broadcast option at the end of the command:

R1(config-if)#dialer map ip 172.12.21.1 name R2 broadcast 5555555

The router will accept that command without the "broadcast" option, but routing protocol updates and hellos would not be able to travel across the line. (This command is also needed in frame relay map statements to allow broadcasts and multicasts to be transmitted.)

PAP is PPP's clear-text authentication scheme, and clear text is a really bad idea. But if you do have to configure it, don't forget that PAP requires additional configuration -the ppp pap sent-username command.

R1(config-if)#ppp pap sent-username R1 password CISCO

Must set encapsulation to PPP before using PPP subcommands

R1(config-if)#

The error message we got while configuring the sent-username command is another important reminder - by default, a BRI line is running HDLC, not PPP. Since HDLC doesn't allow us to use either PAP or CHAP, we'll need to set the link to PPP with the encapsulation ppp command.

R1(config-if)#encapsulation ppp

R1(config-if)#ppp authentication pap

R1(config-if)#ppp pap sent-username R1 password CISCO

But before we configure any of this information, we should configure the ISDN switch-type. Why? Because without the switch-type configuration, it doesn't matter that we avoid the other four errors - the line will not come up. Configure the switch-type with the "isdn switch-type" command, and then verify it with "show isdn status".

R1(config)#isdn switch-type basic-ni

R1#show isdn status

Global ISDN Switchtype = basic-ni (output of this command cut here for clarity)

If you forget this part of the configuration, the output of show isdn status wastes no time in reminding you!

R1#show isdn status

**** No Global ISDN Switchtype currently defined ****

ISDN is an important part of your CCNA studies, and this knowledge still comes in handy in production networks as well. Keep studying, notice the details, run those debugs, and you'll be a CCNA before you know it! Stumble Upon Toolbar

Saturday, December 13, 2008

Cisco CCNA Certification Exam Tutorial: The OSPF Rid

Cisco CCNA Certification Exam Tutorial: The OSPF Rid
OSPF is a major topic on your CCNA exam, as well it should be. OSPF is a widely-used WAN protocol, and you need to learn the fundamentals before moving on to more complicated configurations. One such detail is the OSPF Router ID, or RID.

The RID is the dotted decimal value by which other OSPF routers will identify a given OSPF router. There are some interesting defaults for this value, and a command you should know to hardcode the RID. You had also better know what has to happen for this command to take effect, so let's take a more detailed look at the OSPF RID.

In this example, R1 has an adjacency with R2 and R3 over the 172.12.123.0/24 frame network. R1 is the hub, with R2 and R3 as the spokes. No other interfaces are OSPF-enabled on any of the routers. Running show ip ospf neighbor on R1, we see some unusual values under "Neighbor ID", which is another name for the OSPF RID.

R1#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

3.3.3.3 0 FULL/DROTHER 00:01:57 172.12.123.3 Serial0

2.2.2.2 0 FULL/DROTHER 00:01:57 172.12.123.2 Serial0

Notice the Neighbor ID of each remote address is the loopback address. How can that be if they’re not OSPF-enabled?

When determining the Router ID (RID) of an OSPF-enabled router, OSPF will always use the numerically highest IP address on the router’s loopback interfaces, regardless of whether that loopback is OSPF-enabled.

What if there is no loopback? OSPF will then use the numerically highest IP address of the physical interfaces, regardless of whether that interface is OSPF-enabled.

BOTTOM LINE: An interface does not have to be running OSPF to have its IP address used as the OSPF RID.

The OSPF RID can be changed, but it requires a restart or to reinitialize the OSPF routing process. Use the router-id command to change the default RID of each router as shown, and clear the OSPF process to do so.

R1#conf t

Enter configuration commands, one per line. End with CNTL/Z.

R1(config)#router ospf 1

R1(config-router)#router-id 11.11.11.11

Reload or use "clear ip ospf process" command, for this to take effect

R1#clear ip ospf process

Reset ALL OSPF processes? [no]: yes

1d05h: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or detached

1d05h: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or detached

After entering the router-id command, the router console informed you that you have to reload the router or reset the OSPF processes for this to take effect. You enter the clear ip ospf process command to do this. Notice that when you’re asked if you really want to do this, the prompt is “no”? That’s because all the OSPF adjacencies on this router will be lost and will have to begin the process again. That’s OK on a practice rack, not good in a production network. Don’t use that one at work.

The OSPF RID is not a complicated concept, but the fact that an interface doesn't have to be OSPF-enabled in order to have its IP address act as the RID takes some getting used to. And remember - when the router or switch asks you a question and the prompted answer is "no", take one step back and make sure you really want to do what you're about to do! Stumble Upon Toolbar

Cisco CCNA Exam Tutorial: How To Spend Your Study Time

Cisco CCNA Exam Tutorial: How To Spend Your Study Time
To pass the CCNA exam, you've got to create a study plan. Part of that plan is scheduling your study time, and making that study time count.

You’ve scheduled your exam you’ve created a document to track your study time you’ve planned exactly when you’re going to study. Now the plan must be carried out, without exception.

What exceptions do I mean? Cell phones. Televisions. IPods. Significant others. The list can go on and on.

It’s one thing to have a plan, and an important thing now you’ve got to make sure you carry it out to its fullest potential. That’s easy to say until you’re studying and a friend calls, or you remember that TV show you wanted to watch is on tonight, or you start surfing the Web for Cisco information and end up playing a game.

You MUST make these small sacrifices in order to achieve your main goal, the CCNA. Any worthwhile accomplishment requires some small sacrifice.

TV will be there when you’re done studying. Your significant other will be there when you’re done studying. And believe it or not, people once existed without cell phones! Turn the phone off. Turn your instant messenger service off. Turn your text pager off. Despite what we think, the world can do without communicating with us for 90 minutes. Remember, it’s better to have 90 minutes of great study than 180 minutes of constantly interrupted study. Studies show that while a single phone call causes an 11-minute interruption on average, it takes well over 20 minutes to get back to what you were doing with the proper mental focus. This is true at the office and at your home!

How To Spend Your Study Time CCNA candidates generally spend their time split between book study, practice exams, and lab time on real Cisco equipment. The best study is done by a combination of these, not by overly relying on one. Let’s take a look at each method.

Book study – I’ve never understood why some people (usually the trolls we were talking about earlier) talk about book study like it’s a bad thing. "You can’t learn about technology from books." What a load of manure. You have to learn the theory before you can understand how a router or switch operates. The best way to learn the theory is to read a good book.

At the CCNA level, you doubtless know that you have dozens of choices when it comes to books. Some of the better-known books really do gloss over some important topics, such as binary math and subnetting. Make sure to pick a book or books that go beyond just explaining the theory and that give you a lot of explanation of router configs and real-world examples as well.

Practice Exams: Practice exams are good in moderation, but don’t use them as your main focus of study. Occasionally, I’m asked for study tips by candidates who have taken the exam a few times and not passed yet. I ask them what they’re doing to prepare, and they give a list of companies they bought practice exams from. (You see a lot of this on Internet forums as well.)

Don’t fall into this trap. Practice exams are fine if used as a readiness check, but some candidates just take them over and over again, which renders them basically useless.

On top of that, some of them cost hundreds of dollars. That’s money you’d be much better off spending on Cisco equipment to practice on.

Again, I’m not against practice exams as a supplement to your studies. Just don’t make them the main focus of your study. Taking practice exams over and over and hoping the exam will be just like the practice exam is a recipe for disaster. As I tell my students, when you’re in front of a rack of routers and switches during a job interview (or at 2AM when you’ve been called in to fix a problem), the correct answer is not "D". You’ve got to know what to do.

And how do you learn these skills? Funny you should ask.... Lab Time On Real Cisco Equipment. Again, speaking from experience: This is the most important part of getting your CCNA, succeeding on the job, and going on to get your CCNP.

Getting hands-on experience is critical to developing your networking skills, especially your troubleshooting skills. Although simulators are better than they used to be, they’re still not Cisco routers, and they never will be.

You do your best learning not only when you’re configuring your routers, but when you screw something up.

That’s so important, I want to repeat it – loudly: You do your best learning when you screw something up. Why? Because then you have to fix it that’s how you develop your troubleshooting skills. You can read about all the debug and show commands in the world, but you don’t really understand how they work until you’re figuring out why your Frame Relay connection isn’t working, or your RIP configuration isn’t working.

This is true at every level of the Cisco Learning Pyramid. I can show you the show ip protocols output or what you get when you run debug ip rip, and you might remember it for a little while. But when you use it to troubleshoot a lab configuration, you WILL remember it.

Putting your own practice lab together will also help get you over what I call "simulator question anxiety". If you spend any time on CCNA Internet forums, you’ll see discussion after discussion about these exam questions. To a certain point, this discussion is justified. The simulator questions carry more weight on your exam than any other question while you can earn partial credit on them, you’ve got to get them right or you will most likely fail the exam.

There’s no reason to be anxious about them if you’re prepared. You don’t want to be the person who walks into the testing room that’s scared to have to create a VLAN or an access list you want to be the person who walks into the testing room confident of their ability to perform any CCNA task. The best way to be that confident is to know you’ve done it – on real Cisco equipment.

There are several vendors that sell routers and switches on ebay most of them sell CCNA and CCNP kits that include all the cables and transceivers that you’ll need as well. (And how is a simulator going to help you learn about cables and transceivers?) Keep in mind that you can always sell the equipment after you’re done with the CCNA, or you can add a little equipment to it to go after your CCNP.

Whichever of these methods you use (and I hope you’ll use all of them), make sure to keep them in balance with each other. Don’t depend too much on just one.

On the topic of learning how to troubleshoot… as you run labs on your Cisco equipment, you’ll run into questions or problems that you don’t know the answer to yet. Get used to using Google (or your favorite search engine) to find the answer to these problems - but try to figure it our yourself first!

There’s nothing wrong with asking questions of someone else if you’re not able to find the answer yourself. Trying to find the answer yourself is another important troubleshooting skill you need to start developing today. Don’t be one of these people who posts a simple question on a forum without trying to find the answer on your own. Besides, you get more satisfaction and build more confidence when you determine the answer yourself. Stumble Upon Toolbar

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Cisco Systems, Inc. (NASDAQ: CSCO, SEHK: 4333) is a multinational corporation with more than 63,000 employees and annual revenue of US$35 billion as of 2007. Headquartered in San Jose, los angeles, it designs and sells networking and communications technology and services under two brands, namely Cisco, Linksys, WebEx, IronPort, and Scientific Atlanta.