1 00:00:09,840 --> 00:00:16,920 This is one of multiple videos demonstrating how to troubleshoot issues in preparation for the CCNA 2 00:00:16,920 --> 00:00:17,700 exam. 3 00:00:18,150 --> 00:00:23,970 In this example, we've been told that PC one is not able to ping PC two. 4 00:00:25,170 --> 00:00:26,670 So let's verify that. 5 00:00:28,590 --> 00:00:30,090 Can PC one ping. 6 00:00:30,090 --> 00:00:31,140 PC two. 7 00:00:31,470 --> 00:00:35,730 Notice the you and the dot telling us that it's unreachable. 8 00:00:36,240 --> 00:00:41,280 You means that the traffic is being sent to a router and the router doesn't know where to forward the 9 00:00:41,280 --> 00:00:42,000 traffic. 10 00:00:42,120 --> 00:00:46,530 Let's have a look at the routing table on this router acting as our PC. 11 00:00:46,590 --> 00:00:50,640 Notice in the output we have a default gateway configured. 12 00:00:50,940 --> 00:00:53,400 So can the PC ping the default gateway? 13 00:00:53,430 --> 00:00:54,540 Yes, it can. 14 00:00:54,900 --> 00:00:57,690 So PC one is able to ping router one. 15 00:00:58,020 --> 00:01:03,300 In this topology, I'm using Cisco iOS routers in DNS three. 16 00:01:03,510 --> 00:01:11,940 So rather than trying to set up a physical PC, I'm simply using Cisco iOS V images to act as our PCs. 17 00:01:12,240 --> 00:01:14,250 So on router one. 18 00:01:15,520 --> 00:01:16,180 Let's have a look. 19 00:01:16,210 --> 00:01:17,440 Show IP route. 20 00:01:18,490 --> 00:01:21,340 No routes are being learnt through a routing protocol. 21 00:01:21,430 --> 00:01:28,330 We only see local and connected routes on the router show IP protocols. 22 00:01:29,450 --> 00:01:33,470 OSPF has been enabled as a routing protocol on router one. 23 00:01:33,770 --> 00:01:40,100 A routing protocol would be required to allow rather one to route traffic to this remote network. 24 00:01:40,130 --> 00:01:47,150 So rather two would have to inform router one about that network using a routing protocol of some description. 25 00:01:47,240 --> 00:01:49,580 And in this example, it's OSPF. 26 00:01:51,710 --> 00:01:54,710 On rather to show IP protocols. 27 00:01:55,760 --> 00:01:59,930 OSPF is enabled on this rather show IP route. 28 00:02:00,530 --> 00:02:04,460 It's not learning any routes, however, from router one either. 29 00:02:04,730 --> 00:02:11,120 So looking at this output, are you able to see the problem? 30 00:02:11,330 --> 00:02:15,470 This output should allow you to see where the problem is in this network. 31 00:02:15,470 --> 00:02:18,170 So have you spotted the issue? 32 00:02:20,570 --> 00:02:29,870 Rather one has this rather I'd rather to has this rather id the router ids are the same on both routers 33 00:02:30,080 --> 00:02:40,790 in OSPF rather IDs have to be unique, so show run pipe section OSPF in the output we can see that the 34 00:02:40,790 --> 00:02:48,590 router ID has been configured to 1.1.1.1 show run pipe section OSPF. 35 00:02:49,250 --> 00:02:51,590 The same thing has been configured on router to. 36 00:02:52,960 --> 00:02:55,680 So en route to. 37 00:02:57,990 --> 00:03:05,280 Let's configure the router id as quadruple to notice we're not getting any output when we make changes. 38 00:03:05,790 --> 00:03:09,180 And that's because I disabled logging to the console. 39 00:03:09,330 --> 00:03:11,010 So let me enable logging. 40 00:03:12,950 --> 00:03:15,590 And enable logging this site. 41 00:03:22,600 --> 00:03:24,250 Let's see if we get any output. 42 00:03:24,880 --> 00:03:26,170 So show IPOB. 43 00:03:26,170 --> 00:03:35,020 If neighbour or other neighbour relationship has been established on this side, show ip ospf neighbour 44 00:03:35,050 --> 00:03:37,000 neighbour relationship has been established. 45 00:03:37,240 --> 00:03:44,620 So what I'll do just to show you the problem is I'll set it back to router ID of one and notice we told 46 00:03:44,620 --> 00:03:47,140 that we need to clear the OSPF process. 47 00:03:47,140 --> 00:03:56,020 So clear ip ospf one process. 48 00:03:58,910 --> 00:04:01,190 Notice the neighbor relationship has gone down. 49 00:04:01,670 --> 00:04:08,150 And notice we being told that there's a duplicate router ID and we see that on both sides. 50 00:04:08,390 --> 00:04:13,940 So I purposely disabled logging to the console so that you wouldn't see that. 51 00:04:15,680 --> 00:04:20,810 So before I fix it, this is what the configuration looks like at the moment. 52 00:04:21,410 --> 00:04:25,430 Rather ID is set to 1.1 and 1.1. 53 00:04:25,670 --> 00:04:31,640 So what we should do is change that to quadruple to. 54 00:04:34,060 --> 00:04:39,670 In this case, we didn't have to reset the process because the neighbor relationship hadn't been established 55 00:04:39,670 --> 00:04:40,210 yet. 56 00:04:40,900 --> 00:04:43,360 Notice now the relationship has gone to full. 57 00:04:43,390 --> 00:04:52,660 So we changed the configuration from this to this. 58 00:04:53,530 --> 00:04:57,100 Only difference is rather ID is being changed. 59 00:04:57,370 --> 00:04:58,310 Show IP. 60 00:04:58,330 --> 00:05:01,300 OSPF neighbor. 61 00:05:01,600 --> 00:05:05,320 Neighbor relationship is established on the side. 62 00:05:07,360 --> 00:05:09,280 Neighbor relationship has been established. 63 00:05:09,700 --> 00:05:14,440 If you see output like this, it makes it easy to find where the problem is. 64 00:05:14,470 --> 00:05:18,970 You may not have it that easy in the exam as an example. 65 00:05:19,000 --> 00:05:20,950 You may have to discover where the problem is. 66 00:05:21,040 --> 00:05:22,360 Like I've done here. 67 00:05:22,900 --> 00:05:26,740 So can PC one ping PC two. 68 00:05:26,770 --> 00:05:27,820 Yes, it can. 69 00:05:29,040 --> 00:05:31,830 Let's trace to PC two. 70 00:05:32,130 --> 00:05:33,930 Notice the trace succeeds. 71 00:05:34,350 --> 00:05:38,100 So we've successfully fixed the issue in this network. 72 00:05:38,430 --> 00:05:40,050 I hope you've enjoyed this video. 73 00:05:40,230 --> 00:05:44,520 Please add comments below and let me know if you found this helpful. 74 00:05:44,820 --> 00:05:48,690 Don't forget to subscribe to my YouTube channel for more videos.