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CCNP ENARSI (300-410) : uRPF - VRF AND BFD

1. 8_1 uRPF

In this section, we're going to talk about uRPFRPF, or unicast reverse path forwarding, which is a mechanism for allowing devices to check if the source address is in the local routing table before forwarding it. This is useful to check for source-address spoofing and protect against those attacks. An access list can be specified to allow for specific exceptions. If the RPF check fails, enabling uRPF will stop local requests for the interface unless they have been specifically allowed in the access list or the allow self-request option has been specified.

We have two types of the uRPF: loose mode and street mode. Street Mode checks that the source address has a routing table entry and that the egress interface for the route is the same as the interface the packet was received on. In the loose mode, we only check that the route is in the table before forwarding the packet. Strip mode has implications for asynchronous routing, which is one of the main motivators for using Loose mode. And here is the configuration of URPS; that's pretty straightforward. We just get into interface mode then. Here are we type IP verify unique source reachable via. These are the same in loose mode and strict mode. If you want to use Louis Mode, we type "any," and if you want to use Strict Mode, we type "RX," and that's it.

2. 8_2 VRF Lite Configuration

In our next section, we are going to talk about VRF-lite configuration in IP-based computer networks and virtual routing and forwarding. VRF is a technology that allows multiple instances of a routing table to coexist within the same router at the same time.

Because the routing instances are independent, the same or overlapping IP addresses can be used without conflicting with each other. Network functionality is improved because the network can be segmented without requiring multiple routers. The simplest form of VRF implementation is viral lite. In this implementation, each router within the network participates in the virtual routing environment in a peer-to-peer fashion. While simple to deploy and appropriate for small to medium enterprises and shared data centers, VRFLite does not scale to the size required by global enterprises or large carriers as there is a need to implement each user instance on every router, including intermediate routers.

VRFs were initially introduced in combination with the MLS, but VRF proved to be so useful that it eventually evolved to live independently of the MPLS. Here's what's going on. We have just one physical router, and we have three VRFs, VR of A, B, and C, where A has an independent routing table, V has an independent routing table, and VC has an independent routing table. When a packet comes to this router related to VRFA, that's forwarded by taking a loop to the Vrfa's routing table. And here is the configuration of the VRF Lite. We have voice, data, and video VRS in this router. As you can see, we have just one physical router. But we have three instances of this. We are just defining the virus by typing Ipvref and the VRF name. First IPV data, video, and voice And voice VRF belongs to Villain Two, data VRF belongs to VLAN Three, and video VRF belongs to VLAN Four. As you can see, The second step, in the second step, is defining subintervening, as you can see.

And we are typing Ipvrf, forwarding, voice, data, and video, which are the names of the VRS that I've defined here. And in the last step, if I want to advertise these guys, I'm using, for example, OSPF rather than OSPF 1, a VRF, a VRF name, and the network statements, and that's it. For example, when a packet comes from the VoiceVLAN to this router, it is checked and the packet is forwarded to the VoiceVLAN voice virus. This is the voice virus configuration, and the last thing we're going to talk about is easy. Virtual Network EWM EEM provides traffic separation and pet isolation capabilities on shared network infrastructure. Erien is an IP-based network virtualization solution that takes advantage of existing VRF Lite technology to simplify layer three network virtualization, improve support for shared services, and enhance management and troubleshooting.

And also, EVM reduces the network virtualization configuration significantly across the entire network infrastructure by creating a virtual network trunk. The traditional VRF-light solution recurs, creating one subinterface per VRF on all switches and routers involved in the data path, creating a lot of burden in configuration management. EVN removes the need for the Per VRF subinterface by using the VNet drug interface command. All right, guys, we are coming to the end of our CCMP route sessions. I hope that you liked our training and that you gained so much experience and information about the routing technologies.

3. Bidirectional Forwarding Detection (BFD)

In our next section, we will talk about bi-directional forwarding detection in some networking environments. Guys No carrier detection signalling mechanism is available to quickly detect whether the link between the router and the Internet is down. For example, you can see on the screen that this figure is illustrating three types of environments where a link failure may occur on the directly connected interface when the link failure is not directly connected. And you can see in here that there's an L2-switch network in between two switches, and there is a DWDM network in between two devices. And there are some tunnels configured between two devices, too.

So when the link failure is not directly connected, the router needs to rely on the routing protocol's "keep alive" messages to determine remote and neighbour reachability. This can take an unacceptably long amount of time by today's standards. For example, as you know, OSPF by default waits 40 seconds to declare a neighbour is down guys. But this is a really long time for today's networks. One option for quickly identifying routing protocol neighbour reachable losses is to set the hello and keep-alive timers on the routing protocol to a very short interval. However, introducing fast hellos does not always reduce the failure detection interval to a level where the network can route around the problem before time-sensitive applications notice the communication failure.

In addition, fast hello timers can tax the router's CPU and do not scale well as the number of neighbouring sessions increases. So what are we going to do? What is the solution? The solution is BFD, guys. BFD is a detection protocol that works with all media types, routing protocols, and topologies and encapsulations. It is used to quickly detect reachability failures between two routers in the same layer-3 network, so that network issues can be identified as soon as possible and convergence can occur at a far faster rate. BSD Guys is a lightweight protocol, that is, it has small, fixed-length packets, which means it is less CPU intensive than the fast routing protocol Hellos. So on the screen, router one and router two are using BFD to keep track of reachability. So BFD packets are being sent in an array. You can see in here 100 milliseconds. And if three consecutive packets are missed, BFD reports it as a session failure and notifies EIGRP; the EIGRP timers are set to their defaults of five and 15.

CCNP ENARSI (300-410) : STRUCTURED TROUBLESHOOTING OVERVIEW

1. 1_1- Troubleshooting Methods

Hello everybody. It's time to take a look at the troubleshooting part of the CCMP exam. As you know, CCMP consists of three parts: route, switch, and t-shirt. And it's time to take a look at the shirt now. And the first section is going to be about troubleshooting. Methodical troubleshooting is the process of diagnosing a problem and, if possible, resolving it. The troubleshooting process is usually triggered when a person or a monitoring system reports a problem. While the person reporting the problem often gives clues about the symptoms of the problem, The troubleshooter, the person who is going to have the problem, has defined the root cause of the problem. Let's take a look at how we can approach the troubleshooting process.

The first thing we are going to do is define the problem by getting some information. Then we need to analyse it and eliminate some causes. Then we need to propose a hypothesis and test it. And finally, we need to solve the problem. Gathering information happens after the problem has been reported. Usually the problem report does not contain enough information to formulate a good diagnosis without first gathering more information. The second step is analysis. After the gathered information has been analyzed, the troubleshooter compares the symptoms against his knowledge of the system's processes and the baselines to separate normal from abnormal behavior. The third step is elimination. By comparing the observed behaviour with the expected behavior, some of the possible problem causes are eliminated.

Then we need to formulate a hypothesis. After gathering and analysing information and eliminating the possible causes, one or more potential problem causes may remain. The most likely causal factor is proposed as the hypothetical cause of the problem. Then we need to test the hypothesis. In the 5th step, the hypothesis must be tested to confirm or deny that it is the actual cause of the problem. Now let's take a look at the unstructured tissue approach. In this approach, we define the problem and gather information about it, but we don't analyse it or eliminate steps. We directly jump to the proposed hypothesis and test it. Then we are trying to solve the problem. After a very short period of gathering information, Taking this approach, the troubleshooter quickly makes a change to see if it solves the problem or not. This technique might be quite effective for experienced troubleshooters most times, but it usually does not yield the same results for inexperienced troubled shooters.

And here are the types of structured tissue approach we have: top down Approach, bottom-up, divide, and concierge follow the path, spot the differences, and move the problem forward. If you use top-down, you start from the application layer of the OSI module and go to the bottom. If you use bottom-up, you start from the physical layer of the OSI module and go until the application. If you use DividendConcure, you start from the middle of the OSI module, which is usually the network layer, and you go up or down according to the findings, and we have followed a path approach. As I said, in this method, the troubleshooter simply takes a trace output and tries to uncover problems all the way to the destination, and we have the spot the differences method. As you can see here, in this method, the correct configuration of the network devices is compared to the problematic configuration, with the problems and the differences being focused on. And lastly, we can use the mood problem method. In this strategy, the troubleshooting approach for the mood problem is to observe whether the components physically move and repeat the problem on the transported components. Essentially, the goal of the top-down approach is to find the highest OSI layer that is still working. All devices and processes that work on the layer or layers below are then eliminated.

From the scope of the troubleshooting, it might be clear that this approach is most effective if the problem is on one of the higher OSI layers. It is also one of the most straightforward troubleshooting approaches because problems reported by users are typically defined as application layer problems. So starting the troubleshooting process at the source is a natural thing to do. A drawback or impediment to this approach is that you need to have access to the class application layer software to initiate the troubleshooting process. And if the software is only installed on a small number of machines, your troubleshooting options might be limited. All right, what we're going to focus on in this top-down approach is, for example, that this user reported a problem that he cannot surf on the Internet. All right, if we are using the top-down approach, we need to focus on the application layer of the same module first.

And we ask the user, "Hey, ma'am, what are you using as your browser?" For example, are you using Google Chrome or are you using Opera? Let's say that the guy says, "Hey, I'm using Chrome," and what we're going to offer to this guy is, "Man, can you drive the Opera browser?" OK, the guy tries the Opera browser; maybe the problem is solved or not. If the problem is solved, there's no problem, right? Life is good. But if the problem is not solved, you go to the physical layer of the OSI module by starting from the application layer. Okay, you checked the application layer. Then you need to control the other layers as well. For example, you can control the network layer and ask for the IP address of this guy. Maybe you need to control layer two and the data link layer. And you need to ask for the Mac address of this guy. So you can check the switch configurations or the router configurations, et cetera. And let's take a look at the bottom-up approach now.

Okay, let's say that this guy cannot serve on the Internet again. And let's say that he opened the trouble ticket for you. OK, what we're going to focus on is the bottom-up approach, which starts from the physical layer and continues until the application layer. If you couldn't find the solution, all right, when we're going to ask this guy first this time, it's, "Hey man, can you check your cable that is coming to your PC?" Can you check your Ethernet cable? Are the lights on the Ethernet fine or not? Or is your cable plugged in correctly? Okay, then if the answer is "no" for this guy, okay, plug your cable correctly into your PC, and you'll be able to join the Internet. All right, if the problem still persists, what we're going to do is check the detail link layer this time. All right? If the cable is okay, if life is good, but if I still cannot serve on the Internet, what we're going to focus on this time is OSI layer three, which is the data link layer.

And we can ask for the Mac address of the user. Okay, we can ask this guy, "Hey, Mom, what is your Mac address?" I'm going to check, for example, the switch. All right, if there is no problem with the switch definitions, we can check the upper layer, which is the network layer, and we can check the router configurations. We can ask for the IP address of this guy, and we can check the router interface configurations. Perhaps then we should climb until the application layer of the OSI module. And another troubleshooting method is the dividing context approach. Let's say that this guy reported that he cannot serve on the Internet.

Again, in the dividend Cortier approach, you start from layer three, okay? You can ask the user, "Hey man, what's your IP address?" Tell me. Okay, you take a look at the IP address, and if you find the solution, life is good; there's no problem. But if you cannot find a solution, OK, what is your IP address? For example, this guy said, "Hey, there's no IP address attached to my Internet." I'm taking an IP address like starting with one six nine, which is the iPad address, which means there's a problem with the DHCP options, perhaps. All right, if we can find a solution on the network and layer 3, it's okay. But if we cannot find a solution and if the guy is taking the IP address correctly, we need to take a look at the upper layers. But if the guy cannot obtain an IP address correctly, we can check the lower layers, and we have the "follow the path" approach. In this approach, you are tracing the devices and the packets' paths.

For example, let's say that we have an Exchange server in here and that this guy cannot reach the Exchange server. So the path that was followed by reaching the exchange is this one, as you can see. And we need to trace this path by using a simple trace route or tracer command. And we need to check the hops step by step. And we have also compared configuration approaches by comparing configurations, software versions, hardware, or other device properties between working and nonworking situations and spotting significant differences between them. This approach attempts to resolve the problem by changing the non-operational elements to be consistent with the working ones. The weakness of this method is that it might lead to a working situation without clearly revealing the root cause of the problem. In some cases, you are not sure whether you have implemented a solution that works or not. The compare-configuration approach is not a complete approach. It's however a good technique to use when undertaking other approaches.

One benefit of this approach is that it can easily be used by less experienced troubleshooting staff to at least shed more light on the case when you have an up-to-date and accessible set of baseline configurations, diagrams, and so on. Spotting the difference between the current configuration and the baseline might help you solve the problem faster than any other approach. In this approach, devices are simply replaced, and it is observed whether the problem continues or not. All right? And we have this web component approach. Lastly, and in this method, you change the location of the device and check if this problem still persists or not. For example, let's say that there's a problem with the monitoring device. The monitoring device cannot surf the internet. All right? What we're going to do in this method is just change the location of the monitoring PC to here, for example, and use this cable and this part of the switch, then check to see if the problem is still there or not. Alright, guys, we came to the end of this first session, but what I'm going to show you is a very, very good tool on the internet. When you're going to take the tissue exam, you need to resolve some multiple-choice questions.

Multiple-choice questions You are going to face these guys, and you are going to face a scenario that consists of some tickets. The first one is okay; we know how flexible a multiple-choice question can be. As you know, multiple-choice questions can be asked. For example, they can ask something like that. Which one is not a troubleshooting method? For example, tap down, bottom up, and blah, blah, blah. Okay, this is a multiple-choice question, and what we're going to focus on here is the ticket scenario. Cisco is publishing a demo item for this scenario. OK, what I'm going to do in here is just show you the Cisco website by typing "T-shirt tutorial." And when you type this, you see that there's a tissue demo item page. We opened it. So here is the screen that you will face in the actual troubleshooting exam. Alright, that's the actual screen. But this is a demo item. Shortly, you're not going to face the same topology as this one, but you're going to face a similar one of this topology. All right, we have a scenario here. In this scenario, Tshirtcom has created the best bed network shown in the layer two and layer three topology exhibits. This network consists of four routers on a layer-3 switch and one layer-2 switch. In the IPV-4 layer 3 topology, routers 1234 and DSW1 are running AiGRP with an AS number of 16. Rather, one is running static routing to access devices outside the tissue network and blah, blah, blah blah. In the scenario field, you take an older we loop to the topology, okay? And we also layer two topologies.

They are going to share this guy with YouTube, which consists of the layer 2 connections and the VLAN definitions and something like that. For example, we have a D-switch, and we have a slide, which means access switch W-1 and distribution switch 1 OK, as we can see in here, they are connected to each other from the 19 port, and we have client one and client two, and they are connected to the ASW1, and they are using VLAN pens. All right, something like that. And we have also got IPV4, layer 3 topology, and in here, as you can see, we are seeing routers connected to each other, and we can check the IP addresses of the interfaces in here as well. All right, that's the true layer to polish. So what you're going to do in the axiom is solve these tickets. As you can see, we have four tickets here, and each ticket consists of a few questions. Let's start with ticket one. And please keep in mind that in the tissue exam you are not going to make any configurations, guys. You'll just define the problem, and you'll just offer a hypothesis about how to solve the problem.

All right, for example, there's an example question here, and we are saying that the implementation group has been using the test bed to do a PLC that requires both client one and client two to access the web server at blah, blah, blah. After several changes to the interface status for network addressing, routing, and connectivity, a trouble ticket has been opened indicating that client one cannot pin the IP address. As you can see, use iOS commands to isolate the cause of this fault and answer the following questions: On which device is the fault condition located? Are you opening the topologies in here and checking the devices step by step? For example, if you want to control the router for yourself, you can open it and check the status, pink some IP addresses, make some trace routes, and something like that. Okay? When you find the problem in the question, you choose your answer and click on the next question button, and this time it's asking almost the same thing, but it's saying that as the fault condition is related to the technology, you also need to define the technology to which the fault condition is related to.

For example, let's say that you find that the problem is with the static writing. In the next question, you offer a hypothesis about how to solve the fault condition. For example, let's say that we need to write an IP route or something like that. All right? When you finish a ticket, you get a notice. You have completed the current ticket. Continue to work on the remaining tickets, but in the demo item, you see something like that too. You have answered one out of four questions for this ticket correctly. Note that this information is only presented in this demo item. So you're not going to see something like that in the exam. Okay? When you close it, you can now go ahead with the ticket too. And you're going to solve these tickets too. And that's it. All right, guys, what I need to say to you is to just focus on how you can find the problems and how you can solve them. I just wanted to show you what kind of anxiety you'll face in real life, and that's some really cool stuff by Cisco. Alright, so we are coming to the end of this session, and thanks for wearing.

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