Layer 01 and 03 Troubleshooting Techniques Using Packet Tracer

you you hello snared under your at-home instructor walking you another videocast in this videocast we're going to explore how to troubleshoot and packet tracer to me troubleshooting is the key of understanding or testings ones knowledge on the subject matter this particular case we have two local area networks one over on the left and then this little server connected to the router forms the second local area network we also have another wide area network between these two routers you can think of it as a bridge to connect these two brands together if we have successful communication either one of these web clients should be able to pull up a web page from a web server in order to troubleshoot we need to have some theory to work with that is the same we need to understand how web communication occurs between the client and the server so the server by definition is going to be the area that stores the information in this case the web pages and the client is going to make a request for a web page stored on the web server for this to happen the client uses a web browser it's going to be a layer 7 application so it's going to be using HTTP protocol to be able to transfer or receive web pages or the server that is going to jump down to a layer 4 layer 4 is going to be handling the segmentation of the web page that is the pieces that the server is going to be sending to a client now it's key to understand that these different kinds of connections the group these devices together have different capacities if you will so that is to say like the connection between here and there that router could be a very broad connection and the message to be pretty big so the connection between the routers might be very narrow longer connection so the message has to be broken up so one of the things that TCP does a new transport letter is try to segment the message so that it can squeeze through the Narrows connection on your network later on we'll learn about fragmentation but for now I just want you understand that TCP segments the data uses flow control to make sure that the server or the client doesn't get overwhelmed with data once we get past later for and move yourself down to the layer 3 we're dealing with IP addresses this is a really key area to be checking for when troubleshooting making sure things belong to same logical network making sure the right addresses are assigned to the right devices so maybe a big hand before and beginning to this when it comes to troubleshooting most of the problems are at layer 3 we also do later to the physical address stuff even though we can assign physical addresses for now our switches handle physical addresses so occasionally there might be an hour problem going on or the bar table hasn't been developed so we could use tools like ARP to troubleshoot physical to logical addressing but for most of time it's layer 3 layer 1 could be an issue in fact I like to begin with the layer 1 troubleshooting let's take a look over here on this first way in web client two connecting to the switch as you bunch of red dots to me that's layer one that's layer one troubleshooting before I even look at anything else on my network I got I scratched my head and say what's going on between the client and the switch why aren't they pretty green lights like the rest of them remember green means go so when I see red lights the communication process has stopped so in the layer one I wonder if there's something on my interface card I wonder if there's something wrong at the port of the switch whether the switch port is turned off I could also be wondering if there's something wrong with my cable they used to run cable or is there something wrong with the pair's that I make the cable wrong they terminate it incorrectly so let's look at this for a second client1 which is a PC is connected to the switch and it has green lights but you notice it's a solid black line that's connecting client one to switch 0 but web client to using a dashed line hmm one of my videos I told you that packet tracer represents a crossover cable by a series of dashed lines we've also learned that the only time you ever use a crossover cable is when you're connecting life devices like the rather zero connected to the router one routers routers life devices I used a crossover cable and I did it correctly they got very nice now there is an exception to the rule I really don't call it much of an exception just a clause to connect a router to an end device like a PC or a server you will have to use a crossover cable today a router is a computer it's a special purpose computer because this is a computer and that's a computer they're like devices so you have to connect it with the crossover people allow they do not have to connect the client to a switch with a crossover cable to get rid of that cable I'm going to click on one of the red dots when I do that I have a cable diagonal to my cursor and write them over here this toolbox and hit the delete button I'm asking are you sure you want to do that I'm going to say yes oops I accidentally do the PC will show you how to undo that when that happens I'm up here at the green arrow and brings back to PC but without the connection now there is another safer way to delete a cable from the computer when you hit the red dot or green gun and the moment situation working with you're going to be downloading the cable with you right hit the Escape key on your keyboard and then let the cable go and that will disconnect your device to the other device here I use the Delete key and then I had to come back and hit the undo key it happens so the audio Keys up here it's the green arrow program to the left the counterclockwise well alright so let's get to layer 1 troubleshooting down connecting the client to switch I should be using a straight-through cable like a gift for the client one so I'm going to go down here to lightning bolt I'm going to click on the thick black solid line I'm going to go up here to web client to click on it once I'm going to choose Fast Ethernet 0 mainly I'm going to go to the switch and click on that now we choose Fast Ethernet 2 now we learned in a previous video we can always fast forward time until we get some green lights and like I did just come down here click on the fast-forward button and I got some green lights creat is good green means go I'm happy with that so later one troubleshooting seems to be down I got green lines all through this now the real world you go to the device and see if there is a green light or an orange light some kind of indicator letting you know that the cables plugged in and it's working now you can do it at the switch or you can also do it at the client there should be flashing lights if they're communicating as you can see I'll get some flashing lights here once in a while all right let's go layer to layer to troubleshoot layer to troubleshooting is all about the physical addressing and it deals with switch stuff since this course doesn't really dive into switches and VLANs in the signing of physical addresses we're not going to bother with layer 2 so that's a little sweat off your brow what about layer 3 layer 3 addressing it deals with logical addressing so deal with IP addressing for this particular network now I know that to be the case because I can take my cursor and hover over one of my end devices and a box is going to appear and I see underneath the address column of type of address that I'm using 192 dot 168 got one down one that's telling me this is a v4 address in ipv4 because I have four octet for objects 32 bits more on that later so now let me hover off of that and I'm back to my logical topology hmm the best way to trouble shoot later three stuff is by using two commands ipconfig in the ping command member want to get from the client to the web server we're not going to use the simulation the idea of learning the stuff using packagers is be able to apply it in the real world so I'm not going to be able to see the messages flow from switch two routers around the server no only way I'm going to be able to test this is to make sure they can communicate with each other using the ping command let's quickly do that before I go into the clients I need to develop their address so I'm going to click on client 1 then I'm going to come over here to command prompt by the way if you don't have this on your screen don't forget you gotta come up through the desktop tab click on the desktop tab then the command from unconscious here go ahead click on that now the command I'm going to use is going to be IP config and then I'm going to hit enter oops now remember I only care about three lines you got the address the subnet mask and now I care about the default gateway so I'm going to make a mental note if you're doing this at home grab your note paper give you her book and write this information down web client 1 has an IP address 192.168.1.1 also including your notes subnet mask of 255 dot 255 dot 0 dot 0 while you're at it right the gateway a 192 dot 168 got 1.2 54 remember the Gateway is a device used for packets to leave or to come into our network they're like your front door in your apps separate your house from the public and the public from your house alright so now we have recorded that information I'm going to close out of this window and then the dialog box and we're going to the client when client number two I'm going to click on the desktop tab I'm going to click on the command prompt and type it in the same command IP config oops I'm going to try that again likewise I only care about these three lines the IP address the subnet master the gateway so right next to the other area right web client two on your notebook then write IP address of one ninety two dot one sixty eight dot one dot two underneath that right subnet mask of 255 dot 255 dot 255 Don zero and the default gateway of 0.0.0.0 now if you're stringing along some red fly it should come up first red flag is going to be the subnet mask see the web client number one has a subnet mask 255 dot 255 dot 0 dot 0 this one has 255 dot 255 dot 255 dot 0 the other one a default gateway of one ninety two dot one sixty eight dot one dot 254 this one has zero zero one zero zero so right off the bat I see that these two devices have different configurations should that be a problem let's find out let me go to client one now that I have those two IP addresses ones are the command prompt I'm going to go ping the other device and believe the address was one ninety two dot one sixty eight dot one dot two now before you get carried away take your time and verify that that's the right address for the web client number two because part of troubleshooting is laziness that is we're in a hurry and we didn't take her time to go back to find out what the right IP address should have been and so we thought it was this one it turns out we had the wrong IP address to begin with and you spent days ripping things apart when it was just using the state so 192 dot 168 got 1.2 I'm going to hit enter and I get replies well that's interesting even though we have a different subnet mask I'm getting replies let's close out of that let me go back to what client number 2 I'm going to try flipping the relationship I'm going to go to command prompt and now I'm going to ping one ninety two dot one sixty eight dot one dot one make sure I ended up commanding right so it looks like clients are communicating with each other even though they don't want the same configuration or similar configurations so I wonder why that subnet masks didn't seem to make a difference what's the next step so we got some of the data we know these two are able to communicate with each other because I went to the device paying the other person's address and I get replies well in order for this message to get to here it's got to go through the air hmm unfortunately this is a special device it doesn't have the same operating system as these devices so the commands used to find out the IP address for that router is more of a typing exercise a little bit more elaborate to get to so I'm going to show you a shortcut and packet tracer which I really wish we could do in the real world in order to do that I need to identify what interface this side of the router is being used to connect to that land so I'm going to go to options I'm going to go to preferences and then I'm going to check mark so I'm an airstrip I'm sorry interface tab next to always show important labels now I'm going to close out of this and now I see FA 0 slash 0 this is really important you could want to take Mike of my cursor and hover over that router I see that text box that pops up and I see FA that's Fast Ethernet so FA short for fast 0/0 is up that's why I got a green arrow and it's got an IP address of 192.168.1.2 54 slash 24 the important thing I carry right now is back to the address of one ninety two dot one sixty eight dot one dot 254 so go back to your notebook next to a web client to write router 0 fa 0 slash 0 as an IP address of 192.168.1.2 54 with the subnet mask of 255 255 dot 255 dot 0 remember that slash 24 exit we're going to get to later as last 24 tells me that the first three objects are q50 box okay now let's go to web client number one and we go back for command prompt and let me ping the gateway so ping space one ninety two dot one sixty eight dot one dot teaches before and the identity and I'm get replies that's good that's telling me that the message is able to leave the web point one go to this switch and then hit the router what I'm also you let me go back to the IP config man and I just want to make sure all right guys it's re not seeing much one type here we go so is this computer configured correctly well up to this point the default gateway is 192.168.1.2 54 we close out of that which one of these devices represents the default gateway for those end devices it's this router wasn't this IP address for that interface one ninety two dot one sixty eight dot one dot two fifty four so yes it looks like the client one is properly configured to understand its way out of its network let's be thorough let's check web client - all right we're here one five two let's go back to the command prompt let me pig its gateway ping one ninety two dot one sixty eight dot one dot two fifty four hit enter and I get replies well this is interesting if I type in ipconfig I see that the get what he isn't set up but I'm able to ping it why am i able to paint this rally the reason why I'm able to ping this router is one it is plugged in physically to the same network and two it's configured logically to be on the same network that is this router this this client and that client all have the same network address of one ninety two dot one sixty now I would like to save dot one the most part that's true but this one has an issue it's going to come up later so yes they're allowed to communicate to each other however there's going to be a problem when I want to send a message outside my network why is it going to be an issue this device doesn't understand how to handle messages that aren't local that means they don't belong to that network let's see we need to go outside for network we need to pick something that isn't local because all local communication processes are working both clients can talk to the routers the routers can talk to both clients life seems to be good here at home so in the real world I might call up a friend I might access a public server like google.com and see if I can paint outside my network so I'm going to hover over my server and I'm going to see what their IP addresses like I said I really wish I could do that I wish I can take my hand hover over that device and say oh this one's 192 dot 168 to 254 doesn't happen you'd have to get off your ass go to that computer go to the command prompt and type in ipconfig to get this information but since we're in packet tracer let's take advantage of the resources that we do have at us so go ahead under notebook write back land to web server IP address was so they broke it up for you again one ninety two dot one sixty eight dot 2 dot 254 it's got a gateway address of 192 dot 168 1.2 54 he's got a subnet mask of 255 255 255 0 I know this because that slash 24 you see a slash 24 think 3 255 followed by zero alright now that I have this IP address I'm going to go to the web client one let me go back to the command prompt and I'm going to ping one ninety two dot one sixty eight dot 2 dot 254 then I'm gonna hit enter what should happen is this message should go to the router that router should now pass that message on to the next router that Prowler should pass it to the server and the server should then pass it back to the other Albert rather too so should go quiet to switch to router to router to server back to the router back to the router that's the client let's see if it happened so I brought back my client 1 and I'm getting replies I'm getting replies from 192 dot 168 to duck 254 you notice the first reply failed but I got three other ones so let's hit the upper on rerun that test and see if I got a 100% completion now I'm getting forward pies so look like it took the router some time to communicate with each other and that's why that one failed just took too much time for it to receive all right let's go back to the web client and the Jew and run the same command ok one ninety two dot one sixty eight dot 2 dot 254 you now we notice the last time it took a while for it to happen and we drop the first packet so request timed out sort of anticipating its first time to communicate it with the server 11 second time whew they're a little concerned here three times guess that one wasn't a charm so what am I going to do well now you could go back to my settings and see what's wrong client1 was able to communicate this web server but client two was not remember that ipconfig command that I told you about the Gateway isn't set up if the Gateway isn't set up this router sorry this PC or end device has nowhere to send the messages to it does know that the message is going outside its network how does it know that because the network address of the server is 192 dot 168 to network address for web client number 2 is 192 dot 168 count 1 how do I know the network address is that for the client because underneath those Arquette's others to the device those 255 tells me what part of the IP address network address and what part is the host so just by that this has different last name than me it's outside the family it's outside the network it's outside the network go see the relevant first if it doesn't have the router set up properly it's not going to go see the round so let me close out of this command prompt now let me click on the IP configuration tool and now let me go to the default gateway what am I going to put in here here minimize this am I going to put the IP address the web server am I going to put the IP address of the route 1 or the IP address of the router 0 and if it's an IP address of level 0 which one should I use FA 0 slash 0 or FA 0 slash more well what side of the router is plugged into the web client number 2 the FA 0 / 0 is decide the router that I want so what that IP address let me hover over router 0 so I want the one ninety two dot one sixty eight dot one dot 254 address alright we've learned back web client number two in the default gateway box I'm going to type in one ninety two dot one six dot one dot 254 and close out of this let me go back in command prompt and let me see if I can ping the web server now someone hit the up-arrow ping one ninety two dot one sixty eight dot 2 dot 254 let me hit enter I'm given replies so part of layer three troubleshooting is to make sure that I have the right to fault gateway cell I'm getting the same replies let me close out of that at the web client one yard so I can assume that the message left to PC went to the switch went to router zero traveled across that pathway went to our one router one that's the web server web service exit back in a wave wind that was just pinging but remember we're dealing with web my user should be able to use a web browser to get to this web server so let's open up client one we're at the desktop tab let's click on the web browser icon and in the URL under type in a domain name the domain name of that server which is going to be www-where seems like everything's working let's close that adjust let's close out of this dialog box let's go to web client number two let's go to the web browser let's go back to that URL and let's type in wwe.com and click go just like the one up above this one seems to be working - let me close out of this let me close out of that and it looks like we have successful communication Bost I'm going to tell you've got to be careful about using emulate software that models the that's supposed to model the real world looks like we have a couple of shortcomings with packet tracer this is something you're going to find out later when I click on web client and I click on the command prompt and I type in ipconfig this is the difference of knowing something understanding the theory I should say then just simply following along the first problem I see is the subnet mask is wrong in a real network that would cause an issue this subnet mask should be 255 dot 255 dot 255 dot 0 that is it should be the same subnet mask as my other PC all the devices on the same network should have to save some that mask that's problem number one probably number two let me go back to the web client let me hit the command prompt let me type in ipconfig oops you try that again problem number 2 is in this ipconfig command I should be seeing my DNS address let me close out of that and let me look it up over here using IP can see my DNS is 192 dot 168 to 254 I'm happy about that let me close out of that let me close out of that let me go back to a web client the client number 1 let me go back to the IP configuration and I see my web my DNS server as being one ninety two dot one sixty eight dot 2 dot 254 when I run this command ipconfig I would expect like I do in the real world the DNS server address to appear in there so it does give me the gist of knowledge but when I want complete total troubleshooting I should also have the DNS server address information the way DNS works is it takes domain name and match it to an IP address if I don't have a DNS servers address I don't have a telephone book that is I don't have a way of converting a name into a number so I should expect the DNS server address to appear here it doesn't if you're using dots or even a terminal in iOS 10 it will show you your DNS server information so in packet tracer I had to get that information here under the IP address all right problem number three that I saw in packet reasons I'm not too thrilled about its when I look at this web server and I go to the IP configuration box this gateway address is wrong take a look at the IP address of one ninety two dot one sixty eight dot to 254 remember this router talks to this side of them sorry this server talks to this side of the router let me hover over and give you the IP address of 0/1 the IP address of 0/1 is 192 dot 168 at 2.1 it is not one dot 254 so there's a flaw of packet tracer that message shouldn't come back to conversation for both directions that is the message leaves here come to the server and it comes back this server is not set up correctly that message should fail because the IP address of 192.168.1.2 54 isn't on this side of the router in fact it's over here in order to get over here you got to go through here so one thing I like to do is if you can put your finger on something and you want to be able to communicate to another device your finger should not be able to pick up that is in order for me to get from here to there I got to go through this wire to this device to this device just switch down to here what's happening is I'm going from here there and that isn't work I have to go through this device so I'm a little upset that this particular version packet tracer has a very sort of silly flaunted part of learning networks is to be able to troubleshoot it important learning this curriculum is to use packet tracer like you would in the real world so you should be able to come over here on the server and see that oh that's the wrong gateway address whoops should the gateway address be let me hover over gateway address should be 2.1 let me go back there change this to be dot 2 got one and then let me close out of this and that should be able to communicate with this router from back again so really upset that Cisco dropped the ball here on this packet tracer because you should be able to trust in packet tracer that what you've learned in the book to apply here so warning you now packet tracer jars have flaws and this is a serious flaw when I came here to there it should have failed when I came from here to there it should have failed it should have made it to this router and to that server but it should have made its way back I'm really disappointed that it did let's go back to the client web client number one let's go back to the IP configuration let's fix the subnet mask the subnet mask should be 255 dot 255 dot 255 dot zero what about the DNS server having a different IP address in a gateway it's quite possible your DNS server can exist outside your network so that is kosher having a one ninety two dot one sixty eight dot 2 dot 234 as an IP address for your DNS what doesn't or what is not kosher is having a gateway that's outside your network because remember that gateway is a way out of your house another way of looking at that doping a house without any doors to get into it doesn't make any sense so you build yourself in now you can't leave your home so in order to get outside you have to have a door you have to have a gateway and that gateway has to be reached you can't just put a door on the second floor and not upstairs getting to the second floor so you need to make sure that the IP address of your gateway is a local IP address in other words it uses the same logical network address as your other devices since I'm using three 255 the first three op ket's of my IP address need to be the same let's check that 192.168.1 good 192 dot 168 got one great next thing we need to check is no two devices on my network have the same ip address pieces our web client number one as an address of dot one a gateway has an address of dot 254 it close out of that and go back to web client two and then click on IP config one ninety two dot one sixty eight dot one that makes me happy those three devices and to save network address dot to a unique address happy subnet mask the same subnet mask 255 dot 255 dot 255 dot zero thrilled with all Gateway is it this device it is it on the right side of that device hover over that device 192 dot 168 1.2 54 great I'm happy this network is now properly configured let me go back there and check to see what the DNS server is one ninety two dot one sixty eight dot 2 dot 254 so looks like these two clients are using the same DNS server do they have to know part of troubleshooting when you get to the application layer is probably trying a different game a server like using the Open DNS server to see if that one's working and not your ISPs DNS so local area network one is in good shape I know it's in good shape because I'm trusting the rules of IP the internet protocol should say let me go back over here I'm going to click on the web server and click on IP configuration YP address is 192 dot 168 got to 254 hmm can we see that IP address somewhere yeah that was the DNS address for my web clients all right so what you're telling me is that this server is not only a web server but it's also a DNS server and it's quite possible a computer's becoming powerful enough that they can have multiple services running on one machine I'm alright with that interesting it's using its own IP address back for its own DNS server so it's just saying to myself so how do I get through this domain name that's all legitimate subnet mask 255 dot 255 dot 255 dot 0 does that have to be the same subnet mask as the other local area network over here no it's just by chance that they are what about the 192 dot 168 2.1 is that the right gateway address well to verify that I gotta look for the FA 0 slash once IP address of that matter I will take my cursor hover over router 1 what I see is a season and 0/1 has an IP address of 192 dot 168 got two down one so this local area network is partly convenient as far as we're concerned this area here is configured that's beyond the scope of what we want to accomplish with local area network troubleshoot keeping our troubleshooting simple we start off with internal and we work our way up to a destination I like to start with layer 1 to make sure that all my physical connections are correct the right wires and configured correctly or terminated correctly plugged into the right ports the ports are turned on I skip over layer 2 because once again that's the unstow of this course I'll go into layer 3 troubleshooting we add you later through troubleshooting is by using two commands ipconfig and ping eventually a large another command called traceroute but for now I'm just using that and when I do it I'm paying myself I paid my neighbor then I paint my gateway I stop each step away let me come across a hurdle or a request timed out and I try to narrow it down that is if I wasn't successful pinging myself little check my configuration make sure improperly set up but at the driver setup next I'll put my neighbor wasn't successful there I'll check to see if they're properly configured see if I bent the right cables the seat things are turned on after I pay my neighbor I'll ping my gateway what if you have a situation like here with a web server in the river and that's all you have your network that's cool just pin your router that's your neighbor and it's also your gateway so you're doing two things at once it's a good idea to do that to save some time take your time especially to troubleshoot escalate start down blow stuff and work your way up you got another device on there and the other device all right after I did that I went over to the router life was good now I pink outside my network I skipped the step in this troubleshooting because we haven't learned about router configurations just yet in the future which you would ping is the public side of the router this is all stuff you can do at home before you call your cable company up or your internet service provider that helps save a lot of time and money you if you're able to pick up to that point anything beyond that is going to be out of your house with one exception you have to make sure you can get to your jeene server you can't get to your DNS server in your DNS service outside rails and you get to everything including the public side of your router then that's out of your hands and that's when you call your company up and say look I've been able to ping everybody on my network including the router both private and the public side but I can't get to your DNS server I can't get to your router I can't get to your server now what if you're able to ping everything using IP addresses but you can't get to a web page that becomes a domain problem and now you going to look at you ki NS and that becomes a way you're set in troubleshooting so in this video we just learned about layer 1 and layer 3 troubleshoot

Channel: Nicholas Andre

Views: 24,863

Rating: 4.9159665 out of 5

Keywords: Packet Tracer, Cisco, Network, Troubleshooting, Nicholas Andre, CCNA

Id: S2EPVFIi_DA

Length: 42min 33sec (2553 seconds)

Published: Tue Sep 10 2013