1 00:00:09,470 --> 00:00:12,770 This is one of multiple OSPF troubleshooting videos. 2 00:00:13,220 --> 00:00:21,310 In this scenario we've been told that router one is not able to ping router four so let's test that 3 00:00:21,350 --> 00:00:23,060 can write a one ping. 4 00:00:23,060 --> 00:00:32,870 The loopback of rotter for answer is no show IP route we are receiving OSPF root, so we receiving a 5 00:00:32,870 --> 00:00:35,060 route for the loopback of router two. 6 00:00:35,840 --> 00:00:41,420 We're receiving a route for Network ten 1 to 0, but we're not receiving other routes. 7 00:00:42,340 --> 00:00:47,500 Show IP ospf neighbor confirms that we have a neighbor relationship to router two. 8 00:00:48,280 --> 00:00:57,320 So as an example, we can ping the loopback of router to all disable IP domain lookup to make trace 9 00:00:57,460 --> 00:00:59,770 root complete quicker. 10 00:01:00,430 --> 00:01:04,510 And let's see if we can trace to router four. 11 00:01:05,269 --> 00:01:08,870 The trace in this example will not leave the local router. 12 00:01:09,480 --> 00:01:16,470 Because we don't have a gateway of last resort and we don't have a specific route to quadruple for. 13 00:01:16,620 --> 00:01:20,160 So the trace is simply dropped at the local router. 14 00:01:21,020 --> 00:01:28,160 Now what about rather to show ip ospf neighbor rather to has a neighbor relationship to router one but 15 00:01:28,160 --> 00:01:30,650 doesn't have a neighbor relationship to router three. 16 00:01:32,140 --> 00:01:34,040 Ken brought a two ping. 17 00:01:34,060 --> 00:01:35,050 Rather three. 18 00:01:35,080 --> 00:01:36,320 Yes, it can. 19 00:01:36,340 --> 00:01:39,430 So it doesn't look like it's an IP connectivity problem. 20 00:01:40,480 --> 00:01:42,100 It looks like it's something else. 21 00:01:42,130 --> 00:01:44,230 Ken writer three ping rather two. 22 00:01:44,260 --> 00:01:45,860 Yes, it can show. 23 00:01:45,880 --> 00:01:47,590 IP ospf neighbor. 24 00:01:48,040 --> 00:01:53,140 Writer three has a neighbor relationship to write of four but not to router two. 25 00:01:53,500 --> 00:01:56,950 So we definitely have a problem between writer two and writer three. 26 00:01:58,330 --> 00:02:06,640 So in order to show IP OSPF interface brief, OSPF is enabled. 27 00:02:07,670 --> 00:02:12,080 And gigabit is zero zero and gigabit zero one shows. 28 00:02:12,080 --> 00:02:17,990 CDP Neighbours shows us that router three is connected to gigabit zero one. 29 00:02:18,840 --> 00:02:22,110 So OSPF is enabled on that interface. 30 00:02:22,650 --> 00:02:24,810 The local route is a designated router. 31 00:02:25,790 --> 00:02:34,970 Back on road a three show IP OSPF interface brief OSPF is enabled on gigabit zero zero and gigabit zero 32 00:02:34,970 --> 00:02:35,570 one. 33 00:02:36,080 --> 00:02:40,580 We can see that router two is connected to gigabit zero one. 34 00:02:41,650 --> 00:02:48,700 So OSPF is enabled on this interface and the local router believes that it's the designated router. 35 00:02:50,000 --> 00:02:51,650 So we have two routers. 36 00:02:52,390 --> 00:02:56,620 On the same segment thinking that they are the designated writers. 37 00:02:57,970 --> 00:03:01,590 Let's have a look at the interface without brief. 38 00:03:01,600 --> 00:03:04,720 So show IP OSPF interface gigabit zero one. 39 00:03:05,600 --> 00:03:08,360 We can see the IP address of the router. 40 00:03:08,390 --> 00:03:10,670 The area is area zero. 41 00:03:11,150 --> 00:03:13,290 Router ID is this network. 42 00:03:13,310 --> 00:03:14,480 Top is broadcast. 43 00:03:14,480 --> 00:03:15,590 Cost is one. 44 00:03:16,220 --> 00:03:19,220 There's no backup designated router on the segment. 45 00:03:19,700 --> 00:03:22,430 We can see the hollow and other timers. 46 00:03:22,820 --> 00:03:25,460 We can see a lot of other information here. 47 00:03:25,760 --> 00:03:27,070 What about on this side? 48 00:03:27,080 --> 00:03:30,890 So show IP OSPF interface gigabit zero one. 49 00:03:31,760 --> 00:03:33,740 Can you spot the problem? 50 00:03:33,830 --> 00:03:36,950 What's the problem between rather two? 51 00:03:38,710 --> 00:03:40,510 And rather three. 52 00:03:41,120 --> 00:03:44,270 He has rather two years, rather three. 53 00:03:44,870 --> 00:03:46,370 What's the problem? 54 00:03:47,130 --> 00:03:47,520 Okay. 55 00:03:47,520 --> 00:03:54,450 Look at the timers for OSPF to form neighbor relationships, the timers must be the same. 56 00:03:55,170 --> 00:04:01,110 The hollow timer on router three is 30 seconds, whereas it's 10 seconds on router two. 57 00:04:01,950 --> 00:04:03,780 Date interval on the site is 40. 58 00:04:03,810 --> 00:04:05,400 The site is 120. 59 00:04:05,400 --> 00:04:07,680 Wait is 40, 120. 60 00:04:08,100 --> 00:04:10,050 Returns RETRANSMIT is five and five. 61 00:04:10,840 --> 00:04:13,180 Also have a look at the network type. 62 00:04:13,210 --> 00:04:14,620 That's a broadcast. 63 00:04:14,620 --> 00:04:17,200 This is a non broadcast. 64 00:04:18,079 --> 00:04:23,240 If you want OSPF routers to form a neighbor relationship, the timers need to be the same. 65 00:04:24,200 --> 00:04:27,740 Timers can be influenced by the network command. 66 00:04:28,280 --> 00:04:38,840 Ethernet is a broadcast multi axis environment, not a non broadcast environment that would be used. 67 00:04:39,470 --> 00:04:41,810 For free relay as an example. 68 00:04:42,140 --> 00:04:49,700 So we need to set the OSPF network type to broadcast and notice. 69 00:04:49,700 --> 00:04:53,330 As soon as I've done that, neighbor relationships are formed. 70 00:04:54,130 --> 00:04:55,810 If you look at the timers. 71 00:04:57,090 --> 00:05:00,750 Notice the timers here are now the same. 72 00:05:04,200 --> 00:05:07,620 As rather two timers are set the same. 73 00:05:08,890 --> 00:05:11,080 Show IP ospf neighbors. 74 00:05:11,230 --> 00:05:15,340 We have two neighbor relationships, so back on router one. 75 00:05:16,430 --> 00:05:19,160 It's rather one able to trace to quadruple four. 76 00:05:19,580 --> 00:05:20,410 Yes, it is. 77 00:05:20,410 --> 00:05:21,560 So that looks a lot better. 78 00:05:21,560 --> 00:05:25,070 So we can ping quadruple for as an example. 79 00:05:26,100 --> 00:05:28,560 That was an OSPF troubleshooting scenario. 80 00:05:28,590 --> 00:05:31,280 Make sure that your timers are the same. 81 00:05:31,290 --> 00:05:34,140 Check your network types in OSPF. 82 00:05:35,460 --> 00:05:42,150 It's important that the OSPF network types be the same for CNA. 83 00:05:42,570 --> 00:05:48,510 There are some weird and wonderful implementations that you can have with OSPF, but that's not important 84 00:05:48,510 --> 00:05:49,590 for CNA. 85 00:05:50,200 --> 00:05:55,360 Check your network types, check your timers, ensure that they the same between writers. 86 00:05:55,960 --> 00:05:57,400 I hope you enjoyed this video. 87 00:05:57,430 --> 00:06:03,190 If it was of benefit to you, please like it and please subscribe to my YouTube channel. 88 00:06:03,490 --> 00:06:05,290 I wish you all the very best.