1 00:00:00,150 --> 00:00:00,390 Okay. 2 00:00:00,390 --> 00:00:03,090 So in Wireshark we see a whole bunch of messages. 3 00:00:03,090 --> 00:00:08,730 So he has ARP, he has OSPF, CDP, a bunch of protocols being sent on the network. 4 00:00:08,730 --> 00:00:10,590 But I'm going to filter for OSPF. 5 00:00:11,430 --> 00:00:12,990 We've got to rotters. 6 00:00:12,990 --> 00:00:15,000 This is rather to this is rather one. 7 00:00:15,000 --> 00:00:16,740 So let's have a look at rather 1/1. 8 00:00:17,250 --> 00:00:25,050 So rather one is the right on the left hand side frame is IP version four from this MAC address, sending 9 00:00:25,050 --> 00:00:32,280 a multicast to the well known multicast for OSPF, the layer three protocol referenced here is IP version 10 00:00:32,280 --> 00:00:32,850 four. 11 00:00:33,120 --> 00:00:35,790 So at least three we see IP version four. 12 00:00:36,830 --> 00:00:37,820 Source IP address. 13 00:00:37,820 --> 00:00:39,230 Destination IP address. 14 00:00:39,860 --> 00:00:41,750 Protocol number is 89. 15 00:00:42,260 --> 00:00:43,640 That looks good. 16 00:00:44,880 --> 00:00:47,130 That means ospf down to the bottom here. 17 00:00:47,130 --> 00:00:49,110 So let's have a look at OSPF. 18 00:00:49,770 --> 00:00:50,970 Look at the header. 19 00:00:51,890 --> 00:00:57,980 The version is open version two it's a hello packet router IDs this it's got a backbone area. 20 00:00:59,990 --> 00:01:02,480 Password is set to this. 21 00:01:02,480 --> 00:01:03,470 So that all looks good. 22 00:01:03,470 --> 00:01:07,820 So let's have a look at rather to see if we can see a difference. 23 00:01:08,090 --> 00:01:13,550 That all looks great thus far, so we can't see a problem there. 24 00:01:13,550 --> 00:01:18,890 Let's have a look at the hello packet and see if you can see a problem right away. 25 00:01:18,890 --> 00:01:20,420 What's the problem here? 26 00:01:20,420 --> 00:01:21,860 Can you see the issue? 27 00:01:22,400 --> 00:01:31,070 Notice this mask is different now for OSPF routers to form neighbor relationships, they have to use 28 00:01:31,070 --> 00:01:32,480 the same subnet mask. 29 00:01:33,290 --> 00:01:38,390 This IP address on this side is set to ten 123251. 30 00:01:38,480 --> 00:01:41,960 On this side it's set to ten one, three, two, five, two. 31 00:01:41,990 --> 00:01:44,930 But notice the network masks are different. 32 00:01:45,710 --> 00:01:49,970 If the network mask is different, they are not going to form a neighbor relationship, which means 33 00:01:49,970 --> 00:01:53,900 they're not going to exchange routes, which means it's not going to work. 34 00:01:55,190 --> 00:01:56,070 So what I'll do here. 35 00:01:56,090 --> 00:02:03,140 Actually start a new Wireshark capture so that you can see what it looks like once things are fixed. 36 00:02:03,980 --> 00:02:10,850 So OSPF at the moment we are seeing the problem from the original Wireshark capture. 37 00:02:12,030 --> 00:02:13,710 So in the header. 38 00:02:14,630 --> 00:02:15,860 Let's have a look at the hello packet. 39 00:02:15,890 --> 00:02:18,520 Notice the masks are different. 40 00:02:18,530 --> 00:02:20,540 Different masks over here. 41 00:02:21,520 --> 00:02:24,610 So what I'll do is have a look at these routers. 42 00:02:26,080 --> 00:02:27,490 So there's router one. 43 00:02:31,010 --> 00:02:33,080 And he has rather to. 44 00:02:35,000 --> 00:02:35,170 Okay. 45 00:02:35,420 --> 00:02:42,770 So rather one it to boot it up show ip ospf neighbor notice no neighbor relationship show ip ospf neighbor 46 00:02:42,770 --> 00:02:46,670 no neighbor relationship show ip ospf interface brief. 47 00:02:46,670 --> 00:02:52,910 We can see that OSPF is now running on three interfaces a loopback plus two physical interfaces show 48 00:02:52,910 --> 00:02:56,930 ip ospf interface brief same thing on the side. 49 00:02:57,410 --> 00:03:01,430 So in the OSPF captures, you'll notice that the. 50 00:03:03,030 --> 00:03:09,690 Loopback address is used as the OSPF router ID, even though the IP address that's sending out the multicast 51 00:03:09,690 --> 00:03:12,030 is the physical IP address on the interfaces. 52 00:03:12,390 --> 00:03:16,350 So notice router one has this loopback router as this loopback. 53 00:03:16,590 --> 00:03:24,510 That's fine from an OSPF point of view, but if we have a look at the configuration and let's do it 54 00:03:24,510 --> 00:03:32,520 this way, show interface or IP interface gigabit is zero one on this side and on this side, show IP 55 00:03:32,520 --> 00:03:34,530 interface gigabit is zero zero. 56 00:03:34,560 --> 00:03:38,250 Notice the subnet masks are different. 57 00:03:38,250 --> 00:03:39,510 Slash 26. 58 00:03:40,080 --> 00:03:41,280 Slash 24. 59 00:03:42,270 --> 00:03:45,630 Show run interface gigabit zero zero. 60 00:03:46,380 --> 00:03:55,380 Slash 24 on the side show run interface gigabit zero one slash 26. 61 00:03:55,620 --> 00:03:59,220 So in this side interface gigabit zero one IP address ten 62 00:03:59,220 --> 00:04:05,190 132512552452550. 63 00:04:05,700 --> 00:04:08,490 Hopefully once that happens. 64 00:04:09,350 --> 00:04:12,980 If there are no other problems, the neighbor relationships should be formed. 65 00:04:12,980 --> 00:04:13,820 And there you go. 66 00:04:13,850 --> 00:04:20,870 Notice loading is set to fall, so show IP SPF neighbour neighbour relationship is up. 67 00:04:20,870 --> 00:04:25,250 Show ip ospf neighbor neighbors are up. 68 00:04:25,280 --> 00:04:26,600 Just make this a bit bigger. 69 00:04:27,580 --> 00:04:33,250 So neighbor relationships are formed between the two writers show IP route. 70 00:04:33,460 --> 00:04:38,050 We see OSPF routes in the routing table. 71 00:04:38,410 --> 00:04:39,830 That looks good. 72 00:04:39,850 --> 00:04:46,000 So if we go back to Windows, they should hopefully be able to ping each other, which they can. 73 00:04:46,030 --> 00:04:47,740 The two Windows PCs. 74 00:04:49,390 --> 00:04:52,420 PC one and PC two can now ping one another. 75 00:04:52,870 --> 00:04:59,950 Remember in OSPF, the subnet masks have to be the same for the routers to form neighbor relationships. 76 00:05:00,160 --> 00:05:01,810 The subnet masks are different. 77 00:05:01,810 --> 00:05:03,610 They won't form a neighbor relationship. 78 00:05:04,620 --> 00:05:07,290 Hope you enjoying these troubleshooting videos. 79 00:05:07,530 --> 00:05:11,130 It's important that you know why. 80 00:05:11,130 --> 00:05:11,860 A shock. 81 00:05:11,880 --> 00:05:14,670 It's important that you know your protocols. 82 00:05:15,240 --> 00:05:19,590 I like to say that the best way to learn is to troubleshoot. 83 00:05:19,860 --> 00:05:23,210 And Wireshark is a great way to actually learn what's going on. 84 00:05:23,220 --> 00:05:25,110 Not in theory, but in practice. 85 00:05:25,140 --> 00:05:28,580 This is like running a real physical network and capturing the traffic. 86 00:05:28,590 --> 00:05:30,240 You can actually see what's going on.