1 00:00:00,940 --> 00:00:03,160 I'll start a Wireshark capture again. 2 00:00:05,440 --> 00:00:06,910 On the serial link. 3 00:00:10,680 --> 00:00:13,500 In the output, we can see a hollow packet sent. 4 00:00:15,090 --> 00:00:16,200 By right of one. 5 00:00:16,379 --> 00:00:21,930 So this is an OSPF packet sent to the multicast address for OSPF. 6 00:00:22,320 --> 00:00:27,120 We can see that it's showing as a unicast packet in hdl-c. 7 00:00:27,510 --> 00:00:30,600 The protocol type is IP version four. 8 00:00:31,770 --> 00:00:33,690 We can see the source IP address, destination. 9 00:00:33,690 --> 00:00:34,620 IP address. 10 00:00:36,020 --> 00:00:37,520 Shown here once again. 11 00:00:39,480 --> 00:00:42,030 The protocol type is OSPF. 12 00:00:42,030 --> 00:00:52,320 So it's protocol 89 and the protocol used is OSPF and we can see that it's a hello packet with this 13 00:00:52,320 --> 00:00:53,400 network mask. 14 00:00:54,280 --> 00:00:56,320 And it's from this router. 15 00:00:58,770 --> 00:01:00,270 So looking at the. 16 00:01:01,480 --> 00:01:06,190 TLC messages notice its IP version for as the protocol. 17 00:01:07,560 --> 00:01:09,500 Here is CDP. 18 00:01:09,750 --> 00:01:12,990 Different type here is slope. 19 00:01:12,990 --> 00:01:14,460 A different type. 20 00:01:15,480 --> 00:01:16,950 And once again. 21 00:01:17,990 --> 00:01:20,330 If we ping using IP version six. 22 00:01:21,660 --> 00:01:25,650 His IP version six a different hdl-c type. 23 00:01:27,170 --> 00:01:30,920 What I'll do now is purposely change the encapsulation. 24 00:01:31,940 --> 00:01:34,700 On one side to something else. 25 00:01:35,240 --> 00:01:38,660 So the different encapsulation, but I'll set it to pop. 26 00:01:38,900 --> 00:01:42,080 And what we should notice is that the interface goes down. 27 00:01:42,680 --> 00:01:49,010 We can see that OSPF is saying that the relationship has gone down and that the line protocol has gone 28 00:01:49,010 --> 00:01:49,580 down. 29 00:01:50,450 --> 00:01:52,730 So show interface serial two. 30 00:01:52,730 --> 00:01:53,930 Slash zero. 31 00:01:57,430 --> 00:01:58,150 In the output. 32 00:01:58,150 --> 00:02:03,460 We can see that the physical interface is up, but the line protocol is down. 33 00:02:03,910 --> 00:02:06,070 Encapsulation is PPTP. 34 00:02:06,700 --> 00:02:09,400 This means that we don't have a layer one problem. 35 00:02:09,460 --> 00:02:15,550 The interface is physically connected, but this is showing us that we have a layer two problem, which 36 00:02:15,550 --> 00:02:19,000 in our case is a encapsulation issue. 37 00:02:19,800 --> 00:02:20,580 On this side. 38 00:02:20,580 --> 00:02:21,960 OSPF has gone down. 39 00:02:22,530 --> 00:02:24,090 Show interface serial two. 40 00:02:24,090 --> 00:02:25,290 Slash zero. 41 00:02:28,500 --> 00:02:29,820 So there's the command. 42 00:02:29,850 --> 00:02:34,050 The interface is up physically, but the line protocol is down. 43 00:02:34,800 --> 00:02:42,570 The reason why is the encapsulation on the side is hdl-c, but the encapsulation on the side is PPTP. 44 00:02:43,110 --> 00:02:49,380 So for the interface to be up up you need to ensure that the encapsulation on both sides is the same. 45 00:02:50,560 --> 00:02:56,710 So once again on the side, I'll change it to Hdl-c. 46 00:02:57,770 --> 00:03:01,910 And hopefully what should happen is the interface comes up after a while. 47 00:03:02,270 --> 00:03:05,990 Now that's based on keeper lives, so you may have to wait a while. 48 00:03:08,250 --> 00:03:15,390 Keep the lights on these when interfaces are set to 10 seconds so it can take a few seconds for the 49 00:03:15,390 --> 00:03:18,270 link to either go down or to come up. 50 00:03:18,820 --> 00:03:25,240 Don't know, shut an interface and expect it to immediately be working or immediately to go down. 51 00:03:25,420 --> 00:03:32,050 Wait a few seconds so that keeper lives can traverse the link to ensure that things are working properly. 52 00:03:32,380 --> 00:03:34,960 So the line protocol was upped down at that time. 53 00:03:35,560 --> 00:03:37,810 And notice here it went up. 54 00:03:39,070 --> 00:03:45,550 So always wait a few seconds so that keeper lives can succeed from one side to the other. 55 00:03:46,450 --> 00:03:49,030 The encapsulation is now hdl-c. 56 00:03:49,540 --> 00:03:56,620 On this side we can see that the interface came up, OSPF relationships were formed and if you look 57 00:03:56,620 --> 00:03:57,670 at the interface. 58 00:04:00,180 --> 00:04:04,650 We can see that the interfaces up up encapsulation is TLC. 59 00:04:04,920 --> 00:04:06,330 Notice the keep alive. 60 00:04:07,670 --> 00:04:09,170 In a Wireshark capture. 61 00:04:10,220 --> 00:04:11,390 Scrolling up. 62 00:04:13,470 --> 00:04:18,480 You can see a lot of negotiation taking place between OSPF neighbors. 63 00:04:21,640 --> 00:04:24,700 What I'd like to point out here is notice the keeper lives. 64 00:04:25,630 --> 00:04:29,830 So there's a keep alive sent from one side to the other. 65 00:04:30,250 --> 00:04:32,890 And notice we have sequence numbers for the keeper lives. 66 00:04:32,890 --> 00:04:39,190 So there's an outgoing sequence number and a returned sequence number for the keeper lives. 67 00:04:39,830 --> 00:04:42,260 From one side of the link to the other. 68 00:04:43,150 --> 00:04:46,840 And what you'll notice is that will keep on being sent here. 69 00:04:46,840 --> 00:04:51,670 Notice the sequence number was set to one as the interface came up again. 70 00:04:54,500 --> 00:04:56,810 Here's the OSPF negotiation. 71 00:04:57,110 --> 00:05:04,790 He has the IP version six and negotiation and notice here are the keeper lives continuing a bunch of 72 00:05:04,790 --> 00:05:12,530 OSPF stuff and notice the sequence numbers in the keeper lives because the interface came up again on 73 00:05:12,530 --> 00:05:13,550 router two. 74 00:05:14,300 --> 00:05:16,430 So those keeper lives are shown. 75 00:05:16,850 --> 00:05:21,170 So it's important that both sides have the same encapsulation. 76 00:05:22,400 --> 00:05:26,240 It's important that you check the encapsulation. 77 00:05:26,570 --> 00:05:28,700 Check that the physical interface is up. 78 00:05:28,880 --> 00:05:30,920 Check that the line protocol is up. 79 00:05:31,130 --> 00:05:36,020 And wait a few seconds for the keeper lives to succeed on both sides. 80 00:05:36,290 --> 00:05:42,620 So wait, for instance, half a minute to give it time to settle down and to send and receive keeper 81 00:05:42,620 --> 00:05:43,220 lives.