1 00:00:08,880 --> 00:00:15,000 This is one of a multiple plan or local area network troubleshooting videos. 2 00:00:15,450 --> 00:00:22,230 In this video we have four switches running ingenius three switch one and switch two are configured 3 00:00:22,260 --> 00:00:28,990 as layer three switches switch 3 and switch for configured as lead to switches. 4 00:00:29,130 --> 00:00:32,170 So I could change the symbol as an example 5 00:00:35,510 --> 00:00:39,610 to indicate that that's a layer to switch. 6 00:00:39,630 --> 00:00:50,410 However these four switches are running away Sivi lead to. 7 00:00:50,560 --> 00:00:56,150 And what I've done is simply disable IP routing on switch 3 and switch 4. 8 00:00:56,440 --> 00:01:05,220 So we have four switches in the topology and two Iowas V-Rod is Rato one and Rodek to acting as PCs. 9 00:01:05,260 --> 00:01:10,250 This is a very simple topology where we have a core and an Access Layer. 10 00:01:10,540 --> 00:01:15,700 Typically you would connect the core to the access layer using cross-connect. 11 00:01:15,940 --> 00:01:18,590 I'm not going to do that in the trouble shooting video. 12 00:01:18,610 --> 00:01:26,770 Have a look in my CCN a course which is linked below for a more complex topology running HAARP optimized 13 00:01:26,830 --> 00:01:33,460 spending tree redundancy between the call and the access layer and multiple other options that this 14 00:01:33,460 --> 00:01:37,400 network will suffice for our basic troubleshooting. 15 00:01:37,410 --> 00:01:44,670 So now let's assume that a new hire has made some configuration changes on the network and users are 16 00:01:44,670 --> 00:01:48,410 complaining about a network connectivity issues. 17 00:01:49,070 --> 00:01:58,130 You've been told that to this user 10 1 to 1 in violent 2 he's unable to ping the fuse that has a PC 18 00:01:58,130 --> 00:02:04,670 with IP address turned off one or two 1:57 in the villa and three you've been told that switch three 19 00:02:04,670 --> 00:02:08,000 is connected to switch one as follows. 20 00:02:08,000 --> 00:02:14,920 So which one is connected to switch to and switch to is connected to switch for but as Ronald Reagan 21 00:02:14,920 --> 00:02:17,960 said trust but verify. 22 00:02:18,370 --> 00:02:24,520 And what I like to say is don't trust anything that you've been told about a network until you've checked 23 00:02:24,520 --> 00:02:25,980 it yourself. 24 00:02:26,050 --> 00:02:37,300 So you're not typology a one he's acting as PC one show IP interface brief shows us the IP address on 25 00:02:37,510 --> 00:02:44,760 the gigabit interface that looks right the IP address looks right subnet mask looks right. 26 00:02:44,940 --> 00:02:58,490 Let's see if we can ping 10 at 1 2 3 2 2 which is the IP address of router to acting as PC to. 27 00:02:58,540 --> 00:03:00,530 OK so the ping is failing. 28 00:03:00,640 --> 00:03:03,370 We don't seem to be able to ping that device. 29 00:03:03,610 --> 00:03:05,240 So that piece of information is true. 30 00:03:05,350 --> 00:03:13,960 Show IP ROFFT shows us no routes in the writing table but it shows us that the default gateway is set 31 00:03:13,960 --> 00:03:22,020 to 10 not 1 2 2 5 4. 32 00:03:22,020 --> 00:03:29,660 Now that's because IP routing has been disabled on this router in the apology we've got one acting as 33 00:03:29,660 --> 00:03:31,010 a PC. 34 00:03:31,010 --> 00:03:36,070 So when IP routing is disabled this is what the writing table looks like. 35 00:03:37,190 --> 00:03:41,610 The default gateway has been configured on the PC so that's good. 36 00:03:41,660 --> 00:03:45,720 Let's check if we can ping the default gateway Yes we can. 37 00:03:46,660 --> 00:03:50,170 Now where is the default gateway. 38 00:03:50,230 --> 00:03:53,040 We could try and telnet to the default gateway 39 00:03:56,590 --> 00:04:00,470 and let's try telling that to the right IP address. 40 00:04:00,520 --> 00:04:06,370 So the device is there but we are told that a password is required but none is set. 41 00:04:06,460 --> 00:04:11,980 So hopefully the default gateway and this typologies either switch one or switch to which all of the 42 00:04:12,100 --> 00:04:21,720 call three switches so which one show IP interface brief we can see that villain one violent turn violent 43 00:04:21,730 --> 00:04:24,440 three have an IP address configure. 44 00:04:24,550 --> 00:04:27,950 And that's the IP address on the land too. 45 00:04:28,390 --> 00:04:32,950 So those should be the device that the PC is pinging. 46 00:04:33,040 --> 00:04:40,560 I'll do a debug IP ICMP on that switch and get the pc to ping the default gateway. 47 00:04:40,570 --> 00:04:45,640 Now you need to be careful with debugging in a real world environment. 48 00:04:45,740 --> 00:04:52,360 Yeah because we studding for the CCMA we can simply enable any debug command because that'll help you 49 00:04:52,360 --> 00:04:54,680 learn the debugs that are available. 50 00:04:54,880 --> 00:05:02,570 But in the real world be careful with simply enabling a debug especially on a core device. 51 00:05:02,620 --> 00:05:09,680 You may get so much output on the console that you can't read anything all in a very bad situation. 52 00:05:09,700 --> 00:05:13,260 The device may fall over so we don't want that. 53 00:05:13,700 --> 00:05:16,610 So in the real world be careful with debugging. 54 00:05:17,060 --> 00:05:24,100 OK so the pings do arrive on this default gateway so that's good. 55 00:05:25,280 --> 00:05:30,430 I'm going to turn off IP domain look up in the lab here to make things happen quicker. 56 00:05:31,190 --> 00:05:42,150 And then what we'll do is trace 10 one or two three to two which should be PC to not apology. 57 00:05:42,220 --> 00:05:43,430 Let's see how far it gets. 58 00:05:43,450 --> 00:05:51,360 So it gets to the default gateway which we've now determined the switch one. 59 00:05:51,360 --> 00:06:00,030 So what we should do is update the documentation so we could say that these are the IP addresses on 60 00:06:00,030 --> 00:06:03,740 the villans of that switch. 61 00:06:06,310 --> 00:06:13,300 That once again can be seen on switch one by using the show IP interface brief command. 62 00:06:13,560 --> 00:06:15,060 And there they are once again 63 00:06:19,030 --> 00:06:27,270 the trace route shows us that the traffic gets to the default gateway but then doesn't go anywhere as 64 00:06:28,590 --> 00:06:34,360 let's check if PC to ping its default gateway. 65 00:06:34,460 --> 00:06:43,250 Now a test I like to do is to make sure that the local device can paying the other villain of the default 66 00:06:43,250 --> 00:06:44,240 gateway. 67 00:06:44,240 --> 00:06:56,020 So in other words the PC is in veel and two it's in submit 10 1 2 0 and I'm checking that it can ping 68 00:06:56,500 --> 00:07:02,200 the subnet of the device that we try to go to but this is the IP address of the default gateway into 69 00:07:02,220 --> 00:07:03,840 that villain. 70 00:07:03,850 --> 00:07:11,150 In other words we've proven that interval and routing is working on the last three switch but now let's 71 00:07:11,150 --> 00:07:17,720 check the connectivity of PC to can it get to its default gateway. 72 00:07:17,780 --> 00:07:28,020 So this is Rodda to acting as PC to show IP interface brief IP address looks right per the diagram subnet 73 00:07:28,020 --> 00:07:32,670 mask looks right now that information is once again not shown in the diagram. 74 00:07:32,800 --> 00:07:42,630 So we'd want to add that somewhere and you may want to add that on individual devices or make a note 75 00:07:42,630 --> 00:07:51,450 some way that the subnets have a flash 24 mosque show IP wrote shows us the default gateway of PC to 76 00:07:51,600 --> 00:07:57,050 so Kennet ping its default gateway. 77 00:07:57,090 --> 00:07:58,870 No it can't. 78 00:07:58,930 --> 00:08:04,250 So there's something wrong either here or here. 79 00:08:05,480 --> 00:08:15,390 Or let's have a look at Switch for switch forwards the local access switch show Oppy interface brief. 80 00:08:15,480 --> 00:08:22,260 It has an IP address of 10 1 1 4th can it paying such one in villaine one. 81 00:08:22,290 --> 00:08:31,230 Yes it can show IP Raat default gateways tendered one does wonder too far for Kennet paying $10. 82 00:08:31,230 --> 00:08:40,660 One but three to five four yes it can kinda ping the PC in the villa and three. 83 00:08:40,790 --> 00:08:42,870 No it can't. 84 00:08:42,880 --> 00:08:49,210 So the switch kipping the default gateway into Fillon routing is working on the default gateway but 85 00:08:49,240 --> 00:08:57,030 it can ping the PC traffic from the switch to this PC you'd have to traverse to here to get to the default 86 00:08:57,030 --> 00:08:59,580 gateway and then it would have to come back again. 87 00:09:00,940 --> 00:09:09,460 That's confirm the ports on switch for so firstly show IP interface brief Let's confirm that interfaces 88 00:09:09,460 --> 00:09:09,970 are up. 89 00:09:09,980 --> 00:09:14,360 All interfaces look up including gigabit 0 1 90 00:09:17,610 --> 00:09:21,340 that interfaces up gigabit to 0 0 is up. 91 00:09:21,490 --> 00:09:26,310 Which is the link to the core network pings that were previously so. 92 00:09:26,530 --> 00:09:30,930 So we have an indication that those interfaces are already up and working. 93 00:09:31,090 --> 00:09:38,400 Interface trunk is a trunk to the core on gigabit 0 that looks good. 94 00:09:38,400 --> 00:09:46,300 Let's have a look at the gigabit 0 1 interface show interface gigabit 0 1 switch port this interface 95 00:09:46,300 --> 00:09:51,430 should be in violent 3 Can you see the problem in the south. 96 00:09:51,430 --> 00:09:54,770 Put into face name is gigabit. 97 00:09:54,770 --> 00:10:00,290 0 1 it's enabled us to switch port administer of moders dynamic order. 98 00:10:00,630 --> 00:10:08,820 It's currently acting as a static access port so dynamic trunk protocol or DTP did not negotiate to 99 00:10:08,820 --> 00:10:10,080 form a trunk. 100 00:10:10,170 --> 00:10:16,030 So DTP is on but there wasn't a switch to negotiate trunking with. 101 00:10:16,260 --> 00:10:27,190 Notice the problem access mode villain is one show run interface Gieger bitches are one the sport is 102 00:10:27,200 --> 00:10:29,500 not in villaine three 103 00:10:32,500 --> 00:10:33,290 interface gigabit. 104 00:10:33,330 --> 00:10:37,530 0 1 is currently in Villon 1. 105 00:10:37,540 --> 00:10:49,040 So switch port access land 3 show interface gigabit to 0 1 switch port Port is now an access port in 106 00:10:49,040 --> 00:10:52,900 villans 3 show run interface gigabit to 0 1. 107 00:10:52,920 --> 00:10:54,920 There's our configuration. 108 00:10:55,470 --> 00:11:02,400 Let's check if the local switch can ping that PC at the moment it still can't. 109 00:11:02,400 --> 00:11:10,190 It may take a while for spending tree and other protocols to converge. 110 00:11:10,370 --> 00:11:17,330 So you may just need to wait a bit before you see that there's a problem but spanning tree at this point 111 00:11:17,330 --> 00:11:18,160 looks good. 112 00:11:18,260 --> 00:11:22,200 So it shows GDP neighbors. 113 00:11:22,370 --> 00:11:35,220 We can see that rodded to he's connected to Gigabit 0 1 using gigabit 0 0 show interface gigabit to 114 00:11:35,220 --> 00:11:41,670 0 1 switch port confirms that the port is in violent three. 115 00:11:41,750 --> 00:11:50,070 So let's go back onto the PC and check if it can ping its default gateway. 116 00:11:50,120 --> 00:11:51,120 It can now. 117 00:11:51,350 --> 00:11:57,380 So once again you may just have to wait a little bit before you assume that your change has made any 118 00:11:57,380 --> 00:11:58,110 difference. 119 00:11:59,800 --> 00:12:05,690 Kennet paying wrote a one acting PC one. 120 00:12:05,740 --> 00:12:07,390 Yes it can. 121 00:12:07,420 --> 00:12:14,460 So it looks like we've solved the problem. 122 00:12:14,490 --> 00:12:20,660 We could trace to the PC which didn't work before that now works. 123 00:12:20,680 --> 00:12:28,450 So previously when we traced to 10 1 3 2 it failed at the default gateway. 124 00:12:28,570 --> 00:12:35,650 But now it's working and we could do a ping to prove it. 125 00:12:38,370 --> 00:12:43,550 And do a debug on the side to prove that the traffic arrives. 126 00:12:43,750 --> 00:12:47,720 So that was an example of how to troubleshoot a local area network. 127 00:12:47,770 --> 00:12:53,880 It can sometimes be complicated to troubleshoot a layer two issues but remember to check your interfaces 128 00:12:53,890 --> 00:12:57,900 check your villans check your encapsulations and other videos. 129 00:12:57,910 --> 00:13:01,240 I will show you all the problems that you may encounter. 130 00:13:01,660 --> 00:13:04,390 I need to troubleshoot this topology. 131 00:13:04,720 --> 00:13:06,350 Ok enjoy this video. 132 00:13:06,340 --> 00:13:10,610 If you did please like it please subscribe to my YouTube channel. 133 00:13:10,900 --> 00:13:12,310 I wish you all the very best.