1 00:00:12,070 --> 00:00:18,550 This is one of multiple videos that help you troubleshoot CCNA scenarios in preparation for the CCNA 2 00:00:18,550 --> 00:00:19,300 exam. 3 00:00:19,750 --> 00:00:25,660 We've been told that PC one on the left in this topology is unable to ping. 4 00:00:25,660 --> 00:00:26,680 PC two. 5 00:00:26,950 --> 00:00:32,830 In this topology, I'm using three and Cisco EOS V Routers. 6 00:00:33,700 --> 00:00:38,140 As rather one and rather two and to mimic the PCs in the topology. 7 00:00:40,680 --> 00:00:44,280 And don't trust a user when they tell you something. 8 00:00:44,460 --> 00:00:47,790 As Ronald Reagan said, trust but verify. 9 00:00:48,590 --> 00:00:54,920 We've been told that PC one is not able to ping PC two and we've verified that that's true. 10 00:00:55,220 --> 00:01:01,340 Notice we're getting a U in the output, which means that the traffic is being forwarded to a router 11 00:01:01,460 --> 00:01:04,310 and that router doesn't know what to do with a traffic. 12 00:01:06,030 --> 00:01:08,340 Now to ensure that. 13 00:01:10,000 --> 00:01:18,850 Traceroute runs quickly all disabled IP domain lookup and then we'll run a trace route to PC to notice 14 00:01:18,850 --> 00:01:23,140 that traffic is getting to write a one but is not going any further. 15 00:01:23,470 --> 00:01:25,810 So it looks like there's a problem on Ryder one. 16 00:01:26,890 --> 00:01:27,820 On Router one. 17 00:01:27,880 --> 00:01:29,560 Show IP route. 18 00:01:30,130 --> 00:01:31,210 Show IP route. 19 00:01:31,210 --> 00:01:37,510 Shows us that the only routes in the routing table are directly connected networks and the local IP 20 00:01:37,510 --> 00:01:39,940 addresses on the router. 21 00:01:40,990 --> 00:01:47,260 Because this is a remote network, we need to run routing protocols on router one and router two to 22 00:01:47,260 --> 00:01:48,460 exchange routes. 23 00:01:48,850 --> 00:01:55,660 So router one needs to learn about Network ten 130 from router two. 24 00:01:55,930 --> 00:01:59,410 So on router one, show IP protocols. 25 00:02:00,540 --> 00:02:02,820 Are we running a routing protocol? 26 00:02:03,030 --> 00:02:04,740 And the answer is yes, we are. 27 00:02:04,770 --> 00:02:06,390 We're running OSPF. 28 00:02:06,750 --> 00:02:16,110 OSPF is enabled in area zero on gigabit zero zero and in area one on gigabit zero one. 29 00:02:16,990 --> 00:02:20,560 So show ip ospf neighbor. 30 00:02:21,010 --> 00:02:23,560 We don't have any neighbor relationships though. 31 00:02:23,590 --> 00:02:27,220 Show IP ospf interface brief. 32 00:02:28,600 --> 00:02:38,230 OSPF is enabled on gigabit zero zero in Area zero and it's enabled on gigabit zero one in Area one. 33 00:02:38,230 --> 00:02:39,800 So rather one looks good. 34 00:02:39,820 --> 00:02:44,230 What about router to show IP protocols? 35 00:02:44,920 --> 00:02:50,650 We are running OSPF on the other two, but can you spot the problem? 36 00:02:50,800 --> 00:02:58,660 You should be able to see it in the output of this command to help you show IP OSPF interface brief. 37 00:02:59,350 --> 00:03:04,750 Notice OSPF is not running on any interfaces on router two. 38 00:03:05,110 --> 00:03:06,280 Why is that? 39 00:03:07,780 --> 00:03:09,130 Look at this output. 40 00:03:09,220 --> 00:03:11,310 It's routing for networks. 41 00:03:11,320 --> 00:03:12,190 Ten 42 00:03:12,670 --> 00:03:19,180 .1.0.000 0 to 55. 43 00:03:20,270 --> 00:03:24,590 This means there's an exact match on the first three octets. 44 00:03:24,920 --> 00:03:30,560 In other words, OSPF is only running on network ten 10.0. 45 00:03:31,620 --> 00:03:34,480 Do we have any interfaces in that network? 46 00:03:34,500 --> 00:03:36,720 Show IP interface brief. 47 00:03:37,520 --> 00:03:38,540 No, we don't. 48 00:03:38,660 --> 00:03:43,970 We have an IP address configured as follows and one configured as follows. 49 00:03:44,330 --> 00:03:55,790 OSPF is not running on any interfaces on this router, so run pipe section ospf that allows us to view 50 00:03:55,790 --> 00:03:57,740 the OSPF configuration. 51 00:03:57,980 --> 00:04:03,500 So OSPF has been configured, but notice the network command has been configured incorrectly. 52 00:04:03,980 --> 00:04:08,690 So router ospf one? 53 00:04:08,950 --> 00:04:09,860 No. 54 00:04:13,510 --> 00:04:17,079 Network ten 100. 55 00:04:17,709 --> 00:04:20,950 The command should be ten 100. 56 00:04:22,300 --> 00:04:28,780 002 55 255 Now you don't have to do it that way, but that's one of the options. 57 00:04:30,300 --> 00:04:33,300 Notice suddenly a neighbor relationship is established. 58 00:04:33,750 --> 00:04:39,090 Let's have a look at the output against the show IP OSPF interface and let's rather do a brief because 59 00:04:39,090 --> 00:04:40,320 that's too much output. 60 00:04:40,770 --> 00:04:47,820 Notice OSPF is now enabled on both interfaces of router to show IP protocols. 61 00:04:48,610 --> 00:04:50,230 This looks a lot better. 62 00:04:50,740 --> 00:04:58,480 Show IP OSPF neighbor neighbor relationship is established to write a one show IP route. 63 00:04:58,900 --> 00:05:09,520 We have an inter area route en route to to network ten 110 and en route of one show ip ospf neighbor. 64 00:05:10,000 --> 00:05:14,800 We have a neighbor relationship to ten 131 show IP route. 65 00:05:15,100 --> 00:05:18,370 We have learnt a route through OSPF. 66 00:05:18,550 --> 00:05:21,250 Now notice it's not an inter area route. 67 00:05:21,520 --> 00:05:26,140 The route is in the routing table but it's showing as an intra area route. 68 00:05:26,560 --> 00:05:30,250 Whereas this route is an entire area route. 69 00:05:30,910 --> 00:05:32,830 Can PC one ping? 70 00:05:32,860 --> 00:05:35,860 PC two Answer is yes. 71 00:05:36,100 --> 00:05:40,300 So this is a decision that you would need to make based on your design. 72 00:05:40,930 --> 00:05:51,370 Show IP protocols on router one shows us that OSPF has one interface gigabit is zero zero in area zero. 73 00:05:51,400 --> 00:05:52,540 That's fine. 74 00:05:53,260 --> 00:05:55,870 This interface is in area one. 75 00:05:55,960 --> 00:05:58,480 Whereas on router two. 76 00:05:59,610 --> 00:06:08,730 We have both interfaces in Area zero, so the network works, but perhaps you want to do it this way. 77 00:06:08,730 --> 00:06:19,800 So rather OSPF one network ten 1 to 0 and do it more explicitly and then network ten one. 78 00:06:21,170 --> 00:06:22,250 Three zero. 79 00:06:23,570 --> 00:06:24,950 I'll show you the output in a moment. 80 00:06:24,950 --> 00:06:27,440 If you weren't sure about what I was typing. 81 00:06:27,800 --> 00:06:32,540 So show run section OSPF. 82 00:06:33,600 --> 00:06:37,050 We have two network commands configured. 83 00:06:37,860 --> 00:06:47,550 This network is an area zero based on this command, and this network is in area two based on this command 84 00:06:48,390 --> 00:06:49,630 show, IP. 85 00:06:49,650 --> 00:06:53,550 OSPF Neighbor neighbor relationship is established. 86 00:06:53,550 --> 00:06:58,980 We have an internal area root on router two and on router one. 87 00:06:58,980 --> 00:07:06,090 We now see an entire area root ten 130 slash 24 in other words. 88 00:07:08,410 --> 00:07:09,490 This network. 89 00:07:12,500 --> 00:07:13,190 Is. 90 00:07:14,570 --> 00:07:16,160 In Area Zero. 91 00:07:21,610 --> 00:07:23,170 This is area two. 92 00:07:26,430 --> 00:07:28,920 And this is Area one. 93 00:07:34,270 --> 00:07:39,130 It's important that you update your documentation and make sure that you configure your network correctly 94 00:07:39,130 --> 00:07:40,600 per the documentation. 95 00:07:40,600 --> 00:07:44,560 So to confirm that, show IP protocols. 96 00:07:45,560 --> 00:07:46,560 This is correct. 97 00:07:46,580 --> 00:07:48,290 It's area zero. 98 00:07:48,740 --> 00:07:50,100 This is also correct. 99 00:07:50,120 --> 00:07:51,380 That's Area one. 100 00:07:52,080 --> 00:07:54,840 Show IP protocols on Ryder to. 101 00:07:56,400 --> 00:07:57,840 Output looks as follows. 102 00:07:58,110 --> 00:08:05,220 This network ten 1 to 0 is an area zero, and this one is an area two. 103 00:08:05,430 --> 00:08:07,770 Now, the reason why we have a difference in the output. 104 00:08:09,540 --> 00:08:14,700 Is notice the interfaces on router two don't have OSPF commands on them. 105 00:08:15,060 --> 00:08:23,580 We enabled OSPF in the writing process using the network command, whereas on router one. 106 00:08:26,510 --> 00:08:34,880 OSPF was enabled on the interfaces individually and not under the OSPF process. 107 00:08:35,270 --> 00:08:38,120 Both methods work in IP version four. 108 00:08:38,240 --> 00:08:39,890 In IP version six. 109 00:08:41,200 --> 00:08:46,420 You need to use this method to enable OSPF on individual interfaces. 110 00:08:46,660 --> 00:08:50,950 So that's an example of how to troubleshoot OSPF. 111 00:08:51,400 --> 00:08:53,260 Please comment on the video. 112 00:08:53,290 --> 00:08:55,270 Let me know if it was useful to you. 113 00:08:55,540 --> 00:08:56,830 Please also subscribe. 114 00:08:57,010 --> 00:08:59,470 Thanks for watching and all the very best.