1 00:00:00,690 --> 00:00:02,550 Welcome to this troubleshooting video. 2 00:00:02,580 --> 00:00:08,610 This is one of multiple videos that you'll find on my YouTube channel which help you prepare for the 3 00:00:08,610 --> 00:00:10,110 CCNA certification. 4 00:00:10,680 --> 00:00:16,560 Now, we've been told in this topology that PC one is not able to ping PC two. 5 00:00:16,980 --> 00:00:19,800 So let's do some investigation in this example. 6 00:00:19,830 --> 00:00:23,250 PC one is actually an iOS router. 7 00:00:23,340 --> 00:00:28,000 So I'm running iOS V with Indian as three show IP route. 8 00:00:28,020 --> 00:00:32,820 Shows us that there are no routes on this router acting as a PC. 9 00:00:33,180 --> 00:00:40,320 If you see output such as this default gateway is something and the IP routing table isn't displayed. 10 00:00:40,440 --> 00:00:44,220 But you see something such as ICMP redirect caches empty. 11 00:00:44,250 --> 00:00:50,010 It's probably because routing has been disabled on this router. 12 00:00:50,430 --> 00:00:57,360 So notice this command, no IP routing that simply turns this router into an expensive, very basic 13 00:00:57,360 --> 00:00:58,200 PC. 14 00:00:58,260 --> 00:01:05,110 So if it was a physical router, you essentially disabling the functionality of the router can. 15 00:01:05,129 --> 00:01:06,800 PC one ping. 16 00:01:06,810 --> 00:01:10,110 PC two based on the information that we've been given. 17 00:01:10,830 --> 00:01:18,570 As you can see in the output, it's not able to ping PC to notice we're getting you don't you don't 18 00:01:18,600 --> 00:01:22,230 you you means unreachable. 19 00:01:22,560 --> 00:01:27,810 That means that PC one is forwarding traffic to a router, which could be rather one. 20 00:01:27,870 --> 00:01:33,600 And that router doesn't have a route to the remote network that this host resides on. 21 00:01:34,800 --> 00:01:36,780 Now to speed things up, I'm going to use the command. 22 00:01:36,780 --> 00:01:38,610 No IP domain lookup. 23 00:01:40,460 --> 00:01:44,690 And then I'm going to trace route to 10.1 to 3.2. 24 00:01:45,290 --> 00:01:53,840 So notice we are able to get to write 110 111, but rather one doesn't know where to forward the traffic. 25 00:01:53,840 --> 00:02:01,430 So there seems to be a problem on rather one zone, rather one show IP interface brief. 26 00:02:02,060 --> 00:02:03,290 This looks correct. 27 00:02:03,650 --> 00:02:05,930 This IP address is configured on this interface. 28 00:02:05,960 --> 00:02:07,310 Gigabit is error one. 29 00:02:08,100 --> 00:02:10,350 This IP address is configured on this interface. 30 00:02:10,380 --> 00:02:15,390 Gigabit zero zero can write a one ping router to. 31 00:02:16,440 --> 00:02:18,150 The answer is yes it can. 32 00:02:18,540 --> 00:02:23,160 Initial ping failed because it was doing an op for the MAC address of router two. 33 00:02:24,590 --> 00:02:26,060 So let's have a look at the routing table. 34 00:02:26,060 --> 00:02:33,920 Show IP route in the output, we can see that we only have connected routes and local routes. 35 00:02:34,310 --> 00:02:35,900 No other routes have been learnt. 36 00:02:35,900 --> 00:02:45,320 We only see Network ten 110 and Network ten 120 slash 24 and the local host addresses on the interfaces 37 00:02:45,320 --> 00:02:46,100 of the router. 38 00:02:46,700 --> 00:02:50,630 We don't see a network ten one three is zero. 39 00:02:51,110 --> 00:02:54,020 Are we running a routing protocol on this router? 40 00:02:54,050 --> 00:02:58,340 So show IP protocols shows us that we are running a routing protocol. 41 00:02:58,340 --> 00:03:00,800 In this case it's OSPF process. 42 00:03:00,800 --> 00:03:05,510 One router ID of the router is this it's an area border router. 43 00:03:05,960 --> 00:03:11,030 It has an interface gigabit zero zero in area zero. 44 00:03:11,060 --> 00:03:16,940 In other words, this network here is an area zero and this interface gigabit is zero. 45 00:03:16,940 --> 00:03:18,950 One is an area one. 46 00:03:20,570 --> 00:03:25,040 Show IP OSPF interface brief is another useful command. 47 00:03:25,340 --> 00:03:29,330 This gives us brief information so we can see that gigabit is zero zero. 48 00:03:29,360 --> 00:03:33,410 With OSPF, process one is in area zero. 49 00:03:33,590 --> 00:03:38,870 We can also see the IP address and subnet mask used on that interface. 50 00:03:39,020 --> 00:03:40,760 Subnet masks need to be the same. 51 00:03:40,760 --> 00:03:44,600 An IP version for four routers to form a neighbor relationship. 52 00:03:45,380 --> 00:03:53,240 Gigabit zero one is in area one of OSPF process one and it's got this IP address. 53 00:03:53,600 --> 00:03:56,210 Show IP OSPF neighbor. 54 00:03:56,510 --> 00:03:57,230 No neighbor. 55 00:03:57,230 --> 00:03:58,820 Relationships have been formed. 56 00:03:58,910 --> 00:04:00,830 So OSPF is running on gigabit. 57 00:04:00,920 --> 00:04:05,600 Zero zero of right of one but is not forming a neighbor relationship with of two. 58 00:04:05,810 --> 00:04:10,010 So let's have a look at rather two and see if we can find a problem. 59 00:04:10,370 --> 00:04:13,580 Show IP protocols. 60 00:04:14,450 --> 00:04:19,010 OSPF process one is running on this router and in the output. 61 00:04:19,010 --> 00:04:20,750 Can you see the problem? 62 00:04:21,140 --> 00:04:24,590 You should already be able to determine the problem by that output. 63 00:04:24,980 --> 00:04:30,350 But I'll also use this command show ip ospf interface brief to help you. 64 00:04:31,020 --> 00:04:32,490 Can you see the problem? 65 00:04:33,470 --> 00:04:34,820 Notice on rata one. 66 00:04:34,970 --> 00:04:41,810 This interface gigabit is zero zero is an OSPF area zero on router two. 67 00:04:42,800 --> 00:04:46,460 Gigabit is zero zero is an area two. 68 00:04:46,700 --> 00:04:52,190 It's a requirement in OSPF that both sides of the link be configured in the same area. 69 00:04:53,210 --> 00:05:02,570 So show run interface gigabit zero zero shows us that this interface has been configured in OSPF Process 70 00:05:02,570 --> 00:05:05,450 one but in area two. 71 00:05:05,990 --> 00:05:13,250 Whereas on the side show run interface gigabit zero zero shows us that that interfaces in area zero. 72 00:05:13,610 --> 00:05:21,260 So to fix this, we need to change the area to area zero. 73 00:05:21,260 --> 00:05:25,040 So do show run interface gigabit zero zero. 74 00:05:25,900 --> 00:05:28,120 Notice the OSPF area has changed. 75 00:05:28,840 --> 00:05:32,710 Show IP ospf interface brief. 76 00:05:34,140 --> 00:05:37,830 The area has now been set properly, show IP protocols. 77 00:05:39,160 --> 00:05:48,870 Shows us now that this interface is an area zero, whereas gigabit or zero one is in area to show IP 78 00:05:48,880 --> 00:05:52,870 OSPF neighbor and neighbor relationship has been established. 79 00:05:53,350 --> 00:05:56,230 Now why were we not seeing output on the screen? 80 00:05:56,710 --> 00:06:00,220 One of the reasons for that is that a logging could be disabled. 81 00:06:00,220 --> 00:06:02,560 So do show run pipe include log. 82 00:06:03,580 --> 00:06:06,520 Notice this command has been added to the running config. 83 00:06:06,700 --> 00:06:08,200 No logging console. 84 00:06:08,650 --> 00:06:15,820 I added that on purpose so that you didn't see warning messages on the screen to help you determine 85 00:06:15,940 --> 00:06:17,410 what the problem was. 86 00:06:18,100 --> 00:06:22,660 So now, as an example, if I shut down gigabyte zero zero. 87 00:06:25,430 --> 00:06:30,890 Or rather should remove the no logging console and enable logging. 88 00:06:32,170 --> 00:06:36,610 And now go into the interface and shut it and then no, shut it. 89 00:06:36,970 --> 00:06:42,370 We should see output as in we should see that the interface comes up and there you go. 90 00:06:42,880 --> 00:06:46,060 And we should see that OSPF relationships are formed. 91 00:06:46,330 --> 00:06:47,470 And there you go. 92 00:06:48,770 --> 00:06:52,640 Be careful of your logging if you telnet or ssh to a router. 93 00:06:52,670 --> 00:07:00,170 Don't forget to use the command to monitor so that you see logging on the VI lines. 94 00:07:00,440 --> 00:07:07,730 Logging is enabled by default on the console, but I had purposely disabled it, so things are looking 95 00:07:07,730 --> 00:07:08,060 better. 96 00:07:08,060 --> 00:07:18,890 We have a neighbor relationship show ip ospf neighbor shows us that on the side show ip is. 97 00:07:20,100 --> 00:07:20,730 OSPF. 98 00:07:20,730 --> 00:07:21,380 Neighbor. 99 00:07:21,540 --> 00:07:23,280 Neighbor relationship is there. 100 00:07:23,400 --> 00:07:24,750 Show IP route. 101 00:07:25,750 --> 00:07:34,900 Notice we now see an inter area ospf route to ten 130 via ten 122. 102 00:07:35,500 --> 00:07:39,370 So can this router ping the remote PC? 103 00:07:39,400 --> 00:07:40,480 Yes, it can. 104 00:07:40,900 --> 00:07:44,650 Can PC one ping the remote PC? 105 00:07:44,680 --> 00:07:45,580 Yes, it can. 106 00:07:45,820 --> 00:07:48,850 And when we do a trace, that's also successful. 107 00:07:49,720 --> 00:07:53,260 Let's test in the reverse direction just to make sure everything is good. 108 00:07:54,370 --> 00:07:56,260 That looks fine. 109 00:07:56,560 --> 00:07:58,420 Notice the problem with traceroute. 110 00:07:58,420 --> 00:08:05,050 If you don't disable IP domain lookup, the trace root is going to take a long time while it tries to 111 00:08:05,050 --> 00:08:06,220 resolve the names. 112 00:08:07,790 --> 00:08:11,030 So I've disabled the trace. 113 00:08:11,360 --> 00:08:14,120 No IP domain. 114 00:08:16,810 --> 00:08:17,620 Look up. 115 00:08:19,720 --> 00:08:20,590 Do the trace again. 116 00:08:20,590 --> 00:08:25,300 Notice it's a lot quicker now because it's not doing a domain lookup. 117 00:08:25,870 --> 00:08:26,870 I'll do that again. 118 00:08:26,950 --> 00:08:27,730 There you go. 119 00:08:28,120 --> 00:08:31,690 So PC one sends traffic to router two. 120 00:08:31,870 --> 00:08:34,240 And then it sends traffic to router one. 121 00:08:34,720 --> 00:08:36,760 And it then hits the destination. 122 00:08:39,320 --> 00:08:42,679 So that was an example of troubleshooting. 123 00:08:42,710 --> 00:08:50,090 OSPF Don't forget that with OSPF you can configure it one of two ways. 124 00:08:50,420 --> 00:08:58,850 You can configure it on an interface, as I've done in this example, or you can use the network command 125 00:08:58,880 --> 00:09:00,410 under the writing process. 126 00:09:01,520 --> 00:09:04,760 I'll leave the troubleshooting of that to a separate video. 127 00:09:05,390 --> 00:09:13,010 So if you get a simulation in the exam, make sure that you check that OSPF areas have been configured 128 00:09:13,010 --> 00:09:13,640 properly. 129 00:09:14,090 --> 00:09:15,080 Thanks for watching. 130 00:09:15,500 --> 00:09:17,750 Let me know which videos you want me to record. 131 00:09:17,780 --> 00:09:19,720 And don't forget to subscribe. 132 00:09:20,420 --> 00:09:21,410 All the very best.