In this Cisco CCNA Training video, I’ll go over a situation where you might need to configure stub areas, including the correct usage of the “default-information originate” command, in detail, to control the distribution of default information. I’ll also show you when to use the “always” function.

This video enables you to identify the routers in the network and shows you how to avoid having this problem or experiencing this issue. This is not the time for guesswork, you have to be able to distinguish which router is the DCE and which one is the DTE.

Also while configuring the routers, administrators tend to change the default settings from HDLC to custom. We have to maintain the default CISCO serial encapsulation, which is HDLC. This might also be the reason why the point-to-point OSPF network is not working properly.

Another faux pas while connecting the two routers directly that some administrators tend to commit is not providing the clock rate to the DCE router in the network. If that does not happen, the line protocol is not going to manifest itself. An erroneous command, a wrongly identified DCE – the reason might be either of these or a string of others.

Accurately identifying the controller commands and executing them is critically important to make the connection work, if any of these factors is missing, you will be drifting far away from the desired results. At the end of this video, you will be able to identify the DCE and DTE cable connections, input the clock rate at the DCE end, and rightly configure the routers to be used in a point-to-point network.

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Why OSPF is a Better Choice

Open Shortest Path First (OSPF) is a relatively new kid to the Internet adaptive routing scenario. Classified as an interior routing protocol, this protocol employs link state routing. This protocol was developed mainly because there was a need for non-propriety, high functioning Internal Gateway Protocol (IGP) for the TCP/IP family. In addition, the OSPF protocol made the cut when compared to old, yet stable protocols such as the Routing Information Protocol (RIP), despite the increased complexity of OSPF.

The main aim behind this video is to present the user with the advantages of OSPF and why it is being preferred these days. Things change and this is an example of that fact. Years from now there will be other ways and means in accomplishing these tasks, but OSPF is in the spotlight now. Since the OSPF was introduced as an open standard, not being related to particular providers or vendors, it gave the user unprecedented control over the reaches of a single connected network. The various advantages are summarized here:

• Compared to RIP, which normally has an upper limit of 15 routers (or 15 hops), the OSPF protocol has no such limitation put over it.
• Since OSPF was designed with the aim of handling larger networks, OSPF protocol has the ability to reduce or increase the IP packets being transferred over a time frame.
• Since a Shortest Path First (SPF) algorithm is employed, the OSPF protocol provides the fastest address and is loop-free.
• OSPF uses a Link State Algorithm, and therefore the OSPF coverage diameter is wider compared to the diameter of the RIP.
• The OSPF run network is first broken into 18 pieces or classes.
• The main reason behind the OSPF protocol being faster is that whenever changes are made in the routing tables, only the new or updated values are transferred, instead of sending the entire code.

The above mentioned advantages are just a few, some of the most apparent ones. You will see more when you watch the video.

The main reason for this is to have more of a grasp of this trade. Another reason, which sort of relates to what was just said, is so you are fully qualified for the network administrator position. It is not just about knowing how to pass the exam, but also to give you a superior foundation when you are working in the field.

The problem with commands in either of the methods is the fact that they are very similar in syntax, thus it is not uncommon to become easily confused by them.

Throughout this video, using a dummy network, I will explain the subtle differences of these commands so that you don’t become confused or stuck when setting up the required authentication methods.

One thing that you need to remember is that you cannot have both of the OSPF authentication methods in a network. You either have to use clear text authentication or the MD5. There should not be any ambiguity here, this should not be guess work, and if you make a mistake in the beginning, like long division, the final outcome will be incorrect.

In this video, you will also learn what to do in case the OS that you are working on does not support some of the commands supported by older generations of routers. This is not only important from the exam point of view but is also of crucial importance in real world situations.

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This video aims to educate you on why it is essential to configure the routers in a loopback interface.

A loopback interface is not proprietary, thus in real life situations and advanced studies, you will come across loopback interface problems. This is not a question or concern of if but actually when. This is just an aspect of this industry.

It is also important to understand why a loopback interface is essential in and to a network. These are just some of the problems you will encounter in a loopback interface.

How do you fix them? Well this is what the video is all about. At times, there might be a problem with the Ethernet or some hard coding needs to be done. Throughout this video, you will come across various loopback interface problems in an OSPF network and a variety of ways to solve them. Feel free to watch the video more than once to absorb all the information or pause the video to take notes and to concentrate on what was said. This is an important topic that you need to be familiar with not only for your CCNA exam, but on the job as well.

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In a network, if several equal cost routes exist, traffic by default becomes equally distributed. But in real life scenarios, that is hardly the case. It is just very rare. A large network has multi-cost routes burdening the network. Thus the network, rather than working as a single large network, creates multiple small or minute networks. The backbone or the central point of such a network is termed as Area 0.

In an OSPF network, the Designate Router (DR), as well as the Backup Designated Router (BDR), receives multicast updates from the Area 0. In large networks, it becomes difficult to connect the routers in the most efficient manner so that adjacency is the least. This is achieved by sending the updates to specific DRs and BDRs than sending it to every router in the network. This can be done by tweaking the values in Area 0. The video tells you how this is done in most effective, clear, and simplified manner.

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In case of linked state protocols, there is not any split horizons and poisoned reverse since no one really needs them. Moreover, they would not really work with linked state protocol because linked state routers do not exchange routes, rather they exchange links. This is a key difference here and something that should be pointed out. It also should be understood for clarification sakes. Moreover, the SPF algorithm or the Dijkstra algorithm recalculates loops so fast that the problem of loop formation does not occur.

Now when we refer to linked state protocol, we usually are talking about OSPF, but from the real world point of view, you must also be aware of another linked state protocol – ISIS or IS-IS. These kinds of networks are beloved with Internet Service Providers. In this video, apart from loop prevention using the Dijkstra or the SPF algorithm, you will also learn what IS-IS is; which is integral to this entire field.

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In order to ensure that each neighbor is alive, the OSPF router will send Hello signals to all of its neighbors. If a neighbor responds, the counter is set to zero and the cycle continues. If there is not any response, the moment the strike counter reaches four, an error message is generated which signals an intervention requirement. This is how the process works and it was designed this way. Nothing here is by chance; there is a reason for every action and reaction.

Logically, the Hello and Dead intervals should be the same, but under such circumstances, the relationship between different routers never occurs. Moreover, whenever the Hello interval is changed with appropriate commands, certain errors such as: non-detection of a neighbor might occur.

This video explains what needs to be done under such circumstances by demonstrating a series of commands that are needed for changing the interval timings and then what needs to be done if something happens to go wrong. This does not mean that something will go wrong, but how to correct an error which is basically contingency planning.

This is not any different than being in the military or being a firefighter, there should be a way to correct the error and there should be a counter-plan as well. If something goes wrong, you will know how to salvage the situation.

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Remember, when the router decides that its neighbor is suitable to form an adjacency, full copy of the link-state databases are exchanged between the neighbors. After this stage, the routers are said to be adjacent. In order to show the state in which the OSPF neighbors exist, the show ip ospf neighbor command is used. However, in order to understand the underlying mechanism, it is required that you have some background knowledge regarding:

• Connecting routers using console, vty and aux port
• General IOS configuration issues
• Interpretation of Cisco IOS debug outputs

In the video, the debug ip ospf adj command is issued to examine the formation and state of the adjacency. After typing in this command, it usually takes a while to display whether there is a problem which exists between the router neighbors. In the video, it can be seen that the mismatch exists between the hello parameters being sent between the OSPF neighbors, which were either not received correctly or failed basic sanity checks. If this happens or fails to happen actually, the system will not work as it is supposed to.

One more point which you should keep in mind is that the type of interface employed plays a crucial role in determining the formation of adjacencies, and any problems which might creep in.

The way you use the debug command is highly important. When the debug ip ospf adj command is running, you may not see the router prompt. The undebug all command is used to stop the debugs. There is a lot more to learn, but the video aims at giving you the right start.

Any mistake while configuring the router would mean that the proper adjacency would not be formed and the routers would not identify each other as neighbors. If this does not happen the entire process is broken down and there will be flaws in the network.

Regardless of the fact that whether the link is of broadcast or non-broadcast type, the routers should have matching values to identify each other as neighbors. This video aims at explaining how exactly you need to tell two routers in an OSPF network that they are neighbors. This cannot be taken for granted; this is a pivotal relationship that needs to occur and coalesce.

After watching this video, you will be able to understand what exactly can go wrong in the entire procedure and the pitfalls that need to be avoided. This is not only important from the CCNA exam point of view, but is extremely important in real life situations and work place scenarios and developments.

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A major concern regarding distance-vector routing protocols is the frequency with which the updates are sent out (especially in RIP routers). Now this could be a serious issue, because even though the user did not make any changes, updates will be regularly sent. This is in contrast to the link-state routing protocols, which exchange only the state of the links with their neighbors and the cost associated with it. With “associated costs” it is meant that each node in the network calculates the best logical path to the various possible destinations in the network. This logical path computation for each node generates a map of the entire network, and the algorithm used for computing these paths is known as the “Shortest Path First (SPF)” algorithm, or the “Dijkstra algorithm”.

In case of the link-state routing protocol, on each link-state routing enable router three distinct tables are created. The first table stores the details regarding the directly connected neighbors; the second table holds the topology of the entire network, and the third table holds the actual routing table. The link-state routing protocol finds widespread usage in large networks, since this protocol scores higher when it comes to convergence speed and the reliability factor compared to distance-vector routing protocol, which has an apparent slow network convergence speed.

Still, there are no hard and fast rules that dictate that link-state routing protocol should always be used. There are many scenarios where distance-vector routing protocol is better suited. Therefore you need to analyze various parameters before deciding on which protocol is the most suitable, and this video may prove beneficial in enabling you to make this type of decision with conviction and confidence.

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This is no different than a long division problem or any other mathematical problem that involves a series of steps (determining the null hypotheses). In long division, if you make a mistake on the first sequence of calculations it will have a cascading effect on the rest of the problem and your final result will be incorrect. Learning the basic rules and understanding the information this video is invoking falls under the same ramifications – you have to understand the basics, this information will be needed every step of the way.

For those who do not know, OSPF is the only linked state protocol that you will be learning about in this course, but it is not the only linked state protocol in existence. Thus if you want to know about other linked state protocols, you will have to find out on your own. Right from the basics of OSPF, we will be learning about adjacency problems between many routers, to OSPF authentication, and everything will be covered in detail in this video.

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The Method

A floating static route is another type of static route, the difference lying in the fact that the administrative distance (AD) for this kind of static route is set at a higher value than the value used in the functioning routing protocol. This type of route thus only appears in the routing table if the dynamic route is lost. In order to create a floating static route, we simply add the distance option at the end of the command ip route. This way we change the AD of the static route, but the static route will not appear on the created routing table until and unless the matching RIP routes leave this routing table.

Two Possible Routes

In the video, router 1, 2, and 3 are configured over a RIP version 2 domain, in which router 2 and 3 (the ones on the bottom) are connected through a switch and a frame relay cloud. Routers 1 and 3 are also connected, but RIP is not running over this path. In this configuration, if we see the status of router 1, then we will see that for the same network, router 1 has two possible routes, one each through serial 1 and serial 0. This leads to load balancing, and any data being sent is divided and sent through these routes.

The Advantage

However, if either of the routes fails, the data will not reach the destination. One way to overcome this issue is by configuring the routes as static routes, but if only the static routes are used, the AD of such a route is 1 and it becomes placed in the table immediately and the RIP routes are removed. Using a floating static route becomes advantageous because in this case, the RIP routes are not immediately removed.

Cut in Costs

Floating static routes are extremely useful and can more than pay for their worth; and if used with precision, this could lead to serious decline in overhead costs and related network issues.

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In this video, we first will understand what the limitations of RIP are and how we need to overcome them by understanding it in its entirety. This will not only be useful in exams, but will also come to the rescue while you are working on larger and more complete networks. Slow convergence, routing loops, counting to infinity, and small infinity are some of the issues associated with RIP which we will understand and learn to trouble shoot in this video.

In configuring a network using RIP, timers also play a crucial role in its efficacy & efficiency. In the later part of the video, by understanding the limitations of RIP, we will see how best the router can be configured to derive maximum productivity and effort from the network. We will also see various kinds of problems that you may encounter while setting the timers and the different ways to troubleshoot them to determine the source of the issue.

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Routing Configurations

The command show ip protocols serves as a starting point, to know the status of the configured routers just before you arrive at the scene. There are a lot more associated commands, a better understanding of which can really help you on a significant level when troubleshooting any prevailing issues with the router configurations. This command is mostly used for RIP, or routing information protocol, because of the lack of a substantial number of troubleshooting commands. The syntax is: router#show ip protocols (ignore the brackets).

Further Steps

By using the command show ip route, you can easily generate the entire routing table for any router. In the table which is obtained, the connected routes are indicated by the letter C and the RIP discovered routes by the letter R. Using this command by varying the kind of route you wish to inquire about, you can attain the information which is required & needed. By typing the command show ip route? you will acquire a list of the different types of routes. For example, if you wish to inquire about connected routes, you simply have to type in show ip route connected to complete this process.

The Underlining Theme

Returning to the show ip protocol command, when you type in this command, you get the type of route(s) you are running, the frequency with which the updates are sent, and also the update versions which are sent and received between the different routers. This video aims at clarifying such important functionalities of the show ip protocol, and these functionalities can offer you a more comprehensive outlook on this entire process.

RIP has Taken Over

There are two different types of distance-vector routing protocols, known as the Routing Information Protocol (RIP) and Interior Gateway Routing Protocol (IGRP). The latter protocol is close to extinction now, with major emphasis being laid on RIP. You may find IGRP still being used in some production networks, but this protocol has been removed from the CCNA exams.

A Loop

Before exploring RIP further, it is better to have an idea regarding two distance-vector routing behaviors for loop prevention – route poisoning and split horizon. Routing loops are formed whenever an error occurs in the operative routing algorithm or configuration, and as a result the required path forms a loop. In simple terms, the packet is transmitted continuously within a series of different routers, but is never able to reach the intended destination.

No Data-Packets are Sent

Split horizon is a simple, yet very powerful technique for avoiding routing loops. It prevents the formation of loops by stopping the router from advertising a route back onto the interface from which it was received. Route poisoning is operational when a route in the interconnected network is unavailable or invalid. Logic states that if a route becomes unavailable, any further advertisements of that route would be stopped, but in case of distance-vector routing protocol, that does not happen. What basically happens in route poisoning is that whenever an invalid route is detected, all the routers which are a part of the network are informed that the invalid route has an infinite route metric, which in the case of RIP is denoted by the metric value of 16. As a result, all the constituent nodes of the invalid route seem to be at an infinite distance, and thus no data-packets are sent.

Vital Information

These two loop control protocols are crucial, because even a tiny configuration error could lead to serious issues. This is especially the case for large networks.

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