1 00:00:01,010 --> 00:00:06,800 All sort of one shot capture again on the serial link 2 00:00:10,900 --> 00:00:12,870 in the output we can see a halo packet. 3 00:00:12,870 --> 00:00:16,540 S. by Rotto 1. 4 00:00:16,600 --> 00:00:24,670 So this is a no SPF packet sent to the multicast address for OSPF we can see that it's showing as a 5 00:00:24,670 --> 00:00:33,790 unicast pocket in HGL see the protocol type is IP version for we can see the IP address destination 6 00:00:33,790 --> 00:00:46,910 IP address shown here once again the protocol type is OSPF So it's protocol 89 and the protocol used 7 00:00:46,910 --> 00:00:58,960 is OSPF and we can see that it's a hollow packet with US network mask and it's from the router. 8 00:00:58,990 --> 00:01:04,620 So looking at the HDFC messages notice it's IP version 4. 9 00:01:04,970 --> 00:01:15,460 As the protocol here is CGP different type here is slop a different type. 10 00:01:15,730 --> 00:01:28,330 And once again if we ping using IP version 6 his IP version 6 8 different HLC type what I'll do now 11 00:01:28,330 --> 00:01:35,180 is purposely change the encapsulation on one side to something else. 12 00:01:35,430 --> 00:01:38,810 So the different encapsulations But I'll set it to. 13 00:01:39,090 --> 00:01:45,390 And what we should notice is that the interface goes down we can see that OSPF is saying that the relationship 14 00:01:45,390 --> 00:01:50,070 has gone down and that the line protocol has gone down. 15 00:01:50,670 --> 00:01:53,950 So show interface serial to slash is zero. 16 00:01:57,660 --> 00:02:04,830 In the output we can see that the physical interface is up but the line protocol is down and kept solution 17 00:02:04,830 --> 00:02:06,840 is GPP. 18 00:02:06,900 --> 00:02:09,630 This means that we don't have a layer 1 problem. 19 00:02:09,690 --> 00:02:15,720 The interface is physically connected but this is showing us that we have a layer 2 problem which in 20 00:02:15,720 --> 00:02:19,050 our case is a encapsulation issue. 21 00:02:19,990 --> 00:02:22,560 On the side OSPF has gone down. 22 00:02:22,780 --> 00:02:25,110 Show interface Ciril to slash zero 23 00:02:28,690 --> 00:02:34,910 surveys the command the interfaces up physically but the line protocol is down. 24 00:02:34,930 --> 00:02:42,440 The reason why is the encapsulation on the site is a deal see putting kept solution on the side is Peepy 25 00:02:43,360 --> 00:02:50,520 So for the interface to be up up you need to ensure that thing kept isolation on both sides is the same. 26 00:02:50,780 --> 00:03:00,530 So once again on the side all change at to HDL see and hopefully what should happen is the interface 27 00:03:00,530 --> 00:03:02,540 comes up after a while. 28 00:03:02,540 --> 00:03:04,140 Now that's based on keep alive. 29 00:03:04,220 --> 00:03:12,340 So you may have to wait a while keep alive on these whining faces are set to 10 seconds. 30 00:03:12,620 --> 00:03:18,740 So it can take a few seconds for the link to either go down or to come up. 31 00:03:18,920 --> 00:03:25,520 Don't know shut to an interface and expect it to immediately be working or immediately to go down. 32 00:03:25,700 --> 00:03:32,540 Wait a few seconds so that keepalive can traverse the link to ensure that things are working properly. 33 00:03:32,630 --> 00:03:35,440 So the line protocol was up or down at that time. 34 00:03:35,840 --> 00:03:44,820 I noticed here it went up so always wait a few seconds so that keep alive can succeed from one side 35 00:03:44,820 --> 00:03:53,600 to the other encapsulation is now a deal see on the side we can see that the interface came up always. 36 00:03:53,670 --> 00:03:57,540 Relationships were formed and if you look at the interface 37 00:04:00,400 --> 00:04:02,690 we can see that interfaces are pop. 38 00:04:02,790 --> 00:04:04,950 You kept isolation is HTL see. 39 00:04:05,110 --> 00:04:16,000 Notice the keepalive you know wash or capture scrolling up the can see a lot of negotiation taking place 40 00:04:16,150 --> 00:04:21,800 between OSPF neighbors. 41 00:04:21,860 --> 00:04:25,650 What I'd like to point out here is notice the keepalive. 42 00:04:25,860 --> 00:04:30,120 So there's a keepalive saint from one side to the other. 43 00:04:30,480 --> 00:04:32,990 I notice we have sequenced numbers for the keep alive. 44 00:04:33,090 --> 00:04:41,010 So there's an outgoing sequence number and a returned sequence number for the keep alive from one side 45 00:04:41,010 --> 00:04:47,630 of the link to the other and what you'll notice is that will keep on being sent here notice the sequence 46 00:04:47,630 --> 00:04:54,650 number was set to 1 as the interface came up again. 47 00:04:54,670 --> 00:04:57,240 Here's the OSPF negotiation. 48 00:04:57,310 --> 00:05:06,320 Yes the IP version 6 in negotiation and notice here are the keep alive continuing bunch of OSPF stuff. 49 00:05:06,760 --> 00:05:09,640 And notice the sequence numbers in the keep alive. 50 00:05:10,270 --> 00:05:14,530 Because the interface came up again on Rodda too. 51 00:05:14,530 --> 00:05:16,750 So those keep alive those shown. 52 00:05:17,110 --> 00:05:21,190 So it's important that both sides have the same encapsulation. 53 00:05:22,630 --> 00:05:29,680 It's important that you check in kept isolation check that the physical interface is up check that the 54 00:05:29,680 --> 00:05:36,190 line protocol is up and wait a few seconds for the keepalive to succeed on both sides. 55 00:05:36,520 --> 00:05:43,270 So wait for instance half a minute to give it time to settle down and to send and receive keep alive.