1 00:00:00,510 --> 00:00:06,840 A link site request requesting full LSA information from the neighbouring router. 2 00:00:07,260 --> 00:00:12,930 The neighbouring router will send what's called a link state update, which is a packet that contains 3 00:00:12,930 --> 00:00:18,690 links, state advertisements and as mentioned is typically sent in response to a link state request. 4 00:00:18,900 --> 00:00:24,810 This contains detailed information about the link state database rather than just an overview of it 5 00:00:24,810 --> 00:00:27,180 which was contained in the database description. 6 00:00:27,910 --> 00:00:33,730 Links that acknowledgments acknowledge or confirm receipt of a link state update message. 7 00:00:35,070 --> 00:00:40,440 Now an autonomous system is a grouping of routers under a common administrative domain. 8 00:00:40,800 --> 00:00:47,580 So let's assume that the rat is contained within the blue portion of running OSPF within a single autonomous 9 00:00:47,580 --> 00:00:48,180 system. 10 00:00:48,570 --> 00:00:54,390 They may be connecting to other routers under another administrative domain or another company's control 11 00:00:54,390 --> 00:00:56,190 that is running, for example. 12 00:00:56,870 --> 00:01:00,380 OSPF is an IGP or Interior Gateway protocol. 13 00:01:00,410 --> 00:01:03,170 In other words, it's used within an autonomous system. 14 00:01:03,440 --> 00:01:09,710 So within your organization you may have multiple routers running OSPF within the same autonomous system. 15 00:01:10,600 --> 00:01:11,860 Full scalability. 16 00:01:11,890 --> 00:01:14,590 OSPF Networks are broken up into areas. 17 00:01:14,800 --> 00:01:20,320 Now there's debate about this, but Cisco would recommend never more than 50 routers within a single 18 00:01:20,320 --> 00:01:21,670 OSPF area. 19 00:01:22,150 --> 00:01:27,760 In your studies in the future you may come across different figures, but that's a good rule of thumb 20 00:01:27,760 --> 00:01:28,540 to use. 21 00:01:28,960 --> 00:01:35,500 OSPF uses a hierarchical model in that you always have OSPF area zero. 22 00:01:35,500 --> 00:01:44,080 When you have more than one area, it is possible to run OSPF in another area, let's say area one. 23 00:01:44,080 --> 00:01:46,840 But that's only true if you have a single area. 24 00:01:46,930 --> 00:01:53,680 If you've got multiple areas, you have to have area zero, which is known as the backbone area, all 25 00:01:53,680 --> 00:02:01,030 traffic from one area, let's say area one to another area, let's say area two will traverse the backbone. 26 00:02:01,210 --> 00:02:07,660 So what you do is you break up your network into multiple areas following the physical topology with 27 00:02:07,660 --> 00:02:14,800 the view to optimize summarization and reduce routine table updates and link state advertisements. 28 00:02:15,220 --> 00:02:22,150 Certain types of losses can be contained within an area, so the flooding of Lisas throughout the network 29 00:02:22,150 --> 00:02:26,230 is stopped by breaking up the network into multiple areas. 30 00:02:26,800 --> 00:02:35,320 Routers that border the backbone area and another area are known as area border routers or ABS. 31 00:02:35,740 --> 00:02:43,780 The three routers highlighted here are ABS because they have one interface in Area Zero and another 32 00:02:43,780 --> 00:02:46,120 interface in another area. 33 00:02:47,110 --> 00:02:52,810 One of the advantages of ABS is that they allow for summarization of routes. 34 00:02:53,290 --> 00:03:02,990 If Area one contains routes ten 110 up to ten one 100 zero and in Area two, we have networks 10 to 35 00:03:02,990 --> 00:03:06,640 1 zero, up to 10 to 100 zero. 36 00:03:07,460 --> 00:03:12,080 An Area 310 310 up to ten three 100 zero. 37 00:03:12,380 --> 00:03:20,060 Those roots can be summarized on Abydos, so you could say these 100 roots will be summarized as a single 38 00:03:20,060 --> 00:03:22,370 root on this ABR. 39 00:03:22,400 --> 00:03:27,410 So a slash 16 most is used to summarize these 100 roots. 40 00:03:27,590 --> 00:03:29,300 The same could be done here. 41 00:03:29,330 --> 00:03:33,440 10 to 0 zero slash 16 is a summary of these roots. 42 00:03:33,440 --> 00:03:38,480 And lastly, ten 300 slash 16 is a summary of these roots. 43 00:03:38,750 --> 00:03:43,700 This does require careful planning and good IP design. 44 00:03:45,020 --> 00:03:50,270 This Rada is known as an autonomous system border Rada or SVR. 45 00:03:50,660 --> 00:03:53,270 It borders two autonomous systems. 46 00:03:53,720 --> 00:03:59,300 In this case, we've got RIP on the left hand side and OSPF on the right hand side. 47 00:03:59,810 --> 00:04:05,900 Even if all of these routers, including the router, were within your organization, this router would 48 00:04:05,900 --> 00:04:12,830 still be known as an ACR because it's connecting one routing process rip to another routing process 49 00:04:12,830 --> 00:04:14,630 in this case OSPF. 50 00:04:15,020 --> 00:04:20,149 So from an OSPF point of view, this is an autonomous system border router. 51 00:04:21,140 --> 00:04:29,120 These six routers all have interfaces within Area zero and therefore are known as backbone routers. 52 00:04:29,720 --> 00:04:38,360 When traffic is sent from one area to another area, it has to traverse the backbone to reach the destination. 53 00:04:38,720 --> 00:04:45,890 So these three routers in the backbone are used to allow the traffic to flow from area one to area two. 54 00:04:46,400 --> 00:04:54,710 OSPF once again requires a good design with all areas connecting to the backbone area as traffic flows 55 00:04:54,710 --> 00:04:58,430 from one area to another area through the backbone area. 56 00:04:59,670 --> 00:05:02,880 These highlighted routers are known as internal routers. 57 00:05:03,000 --> 00:05:06,540 They are internal to their specific areas. 58 00:05:07,760 --> 00:05:12,830 OSPF routers use halos to form neighbor relationships or adjacencies. 59 00:05:13,710 --> 00:05:21,030 The Hello protocol once again establishes and maintains neighbor relationships by ensuring bi directional. 60 00:05:21,060 --> 00:05:25,110 In other words, two way communication between neighbors. 61 00:05:25,620 --> 00:05:32,340 Bidirectional communication occurs when a router recognizes itself listed in the packet received from 62 00:05:32,340 --> 00:05:33,090 a neighbor. 63 00:05:33,450 --> 00:05:41,070 How those are sent using multicast address 224005 and contain the following information for neighbor 64 00:05:41,070 --> 00:05:42,360 relationships to be formed. 65 00:05:42,360 --> 00:05:48,690 It's important to remember that certain parameters have to match on both routers. 66 00:05:48,990 --> 00:05:53,460 Now the first field containing a hello is the router ID. 67 00:05:53,880 --> 00:06:02,880 A router ID identifies this specific router and is used in various scenarios in OSPF, including the 68 00:06:02,880 --> 00:06:07,380 election of a designated router or backup designated router. 69 00:06:07,920 --> 00:06:15,900 A router ID is chosen per router based on the highest IP address of any configured interface. 70 00:06:15,900 --> 00:06:24,030 When OSPF is enabled on the router or on the highest loopback interface active on the router when OSPF 71 00:06:24,030 --> 00:06:30,060 is enabled or it can be manually specified using the router ID command. 72 00:06:30,510 --> 00:06:32,850 So to demonstrate that you have a router, right. 73 00:06:32,940 --> 00:06:33,450 One. 74 00:06:35,430 --> 00:06:39,420 Show off the interface brief will show me the relevant interfaces on this router. 75 00:06:39,870 --> 00:06:44,970 And what I'm going to do is I'm going to shut down all the interfaces and show you that OSPF is not 76 00:06:44,970 --> 00:06:50,580 able to select a router ID if the interfaces are all shut down. 77 00:06:57,250 --> 00:07:00,700 So show IP interface brief again. 78 00:07:00,700 --> 00:07:08,170 Shows me that all of my interfaces are administratively shut now in global config mode popping the command 79 00:07:08,170 --> 00:07:08,860 router. 80 00:07:10,500 --> 00:07:11,940 In this case, OSPF. 81 00:07:13,630 --> 00:07:18,370 And a process ID will allow me to enable OSPF on this router. 82 00:07:19,030 --> 00:07:27,490 The process ID allows for the differentiation of multiple OSPF instances running on the same router 83 00:07:27,970 --> 00:07:33,760 that can become important in multi protocol label switching environments or MPLS environments. 84 00:07:34,180 --> 00:07:41,020 For this course you'll only run a single OSPF process on a router, but note multiple processes can 85 00:07:41,020 --> 00:07:42,850 be enabled on errata. 86 00:07:44,170 --> 00:07:46,540 Now notice what the router says. 87 00:07:47,410 --> 00:07:55,750 No router id ospf process one failed to allocate a unique router id and therefore cannot start. 88 00:07:56,720 --> 00:08:06,080 Topping the come on do show IP protocol shows that the writing protocol in use is OSPF one, but the 89 00:08:06,080 --> 00:08:09,260 router ID is 0000. 90 00:08:10,320 --> 00:08:13,200 OSPF is not running correctly on this router. 91 00:08:13,500 --> 00:08:15,770 Show IP interface brief. 92 00:08:17,830 --> 00:08:21,180 Let's enable this interface. 93 00:08:21,190 --> 00:08:22,060 So interface. 94 00:08:22,060 --> 00:08:23,170 If zero zero. 95 00:08:23,260 --> 00:08:23,620 No. 96 00:08:23,620 --> 00:08:24,220 Shut. 97 00:08:25,170 --> 00:08:28,140 So what I'll do is I'll remove OSPF. 98 00:08:30,090 --> 00:08:32,039 And then I'll re-enable, OSPF. 99 00:08:35,190 --> 00:08:36,780 Notice there is no complaint. 100 00:08:37,200 --> 00:08:41,400 Do show IP protocols. 101 00:08:41,970 --> 00:08:47,070 Shows me that the router ID is ten 111. 102 00:08:47,800 --> 00:08:49,780 Do show up to interface brief. 103 00:08:50,810 --> 00:08:55,340 Shows me that this IP address has become the router ID. 104 00:08:55,940 --> 00:09:03,860 The reason why is the router ID is chosen based on the highest IP address of any active interface when 105 00:09:03,860 --> 00:09:05,690 the writing process is enabled. 106 00:09:06,290 --> 00:09:09,530 So if I enabled, for instance, these two interfaces. 107 00:09:20,050 --> 00:09:21,160 As follows. 108 00:09:21,400 --> 00:09:22,960 And then top the command. 109 00:09:24,190 --> 00:09:26,350 Do show IP interface brief. 110 00:09:28,780 --> 00:09:34,510 You'll see that these interfaces, the fast Ethernet interface and the two serial interfaces are up, 111 00:09:34,510 --> 00:09:34,990 up. 112 00:09:36,000 --> 00:09:44,550 Do show IP protocols still shows that the router ID is ten 111. 113 00:09:45,480 --> 00:09:51,780 I've just changed the encapsulation back to its default so hdl-c and the interfaces come up again. 114 00:09:52,260 --> 00:09:58,500 But what I'd like you to see is that the Ryder ID still remains as ten 111. 115 00:09:58,890 --> 00:10:00,480 And I can do that command again. 116 00:10:01,050 --> 00:10:02,700 Do show IP protocols. 117 00:10:03,740 --> 00:10:05,900 Notice the Rada IDs ten 111. 118 00:10:07,200 --> 00:10:07,830 I can do this. 119 00:10:07,830 --> 00:10:08,190 Come on. 120 00:10:08,190 --> 00:10:08,940 Clear. 121 00:10:09,540 --> 00:10:17,340 IP ospf process to clear the OSPF process and let's see if that makes any difference. 122 00:10:17,340 --> 00:10:19,740 So show ip protocol. 123 00:10:21,120 --> 00:10:24,900 And as you can see, the root of ID remains the same. 124 00:10:25,630 --> 00:10:29,290 But if I removed OSPF. 125 00:10:30,290 --> 00:10:32,570 And then re enabled ospf. 126 00:10:36,850 --> 00:10:41,260 Notice the router ID has changed to ten 151. 127 00:10:43,260 --> 00:10:50,640 So what the Rada has done is it looked for the highest IP address on any active interface when OSPF 128 00:10:50,640 --> 00:10:51,570 was enabled. 129 00:10:52,080 --> 00:11:00,300 This time, when OSPF was enabled, ten 151 was the highest IP address on any active physical interface. 130 00:11:00,300 --> 00:11:03,150 So it was chosen as the router ID. 131 00:11:03,900 --> 00:11:05,880 Now what happens if we enable the loopback? 132 00:11:07,410 --> 00:11:10,800 You'll notice the loopback has the lowest IP address. 133 00:11:11,160 --> 00:11:13,950 One is far lower than ten. 134 00:11:15,200 --> 00:11:15,680 So no. 135 00:11:15,680 --> 00:11:19,220 Shut that you show IP protocol. 136 00:11:20,220 --> 00:11:22,320 You can see the Rada ID is stole. 137 00:11:22,320 --> 00:11:23,790 Still ten 151. 138 00:11:24,000 --> 00:11:24,990 I'll do it again. 139 00:11:25,470 --> 00:11:28,260 Rada ID is still ten 151. 140 00:11:29,930 --> 00:11:32,090 But if I remove OSPF. 141 00:11:33,140 --> 00:11:34,730 And then re-enable it. 142 00:11:37,520 --> 00:11:40,730 Notice the radar ID is now quadruple one. 143 00:11:45,280 --> 00:11:46,720 So the rule again. 144 00:11:47,550 --> 00:11:56,490 OSPF router ID is chosen based on the highest IP address of any physical interface that is active when 145 00:11:56,490 --> 00:11:58,590 the OSPF process is enabled. 146 00:11:59,010 --> 00:12:07,830 But if there is a loopback that is active, the loopback overrides the physical interfaces and the loopback 147 00:12:07,830 --> 00:12:08,970 is used as the router. 148 00:12:09,000 --> 00:12:16,230 ID loop backs have the advantage that they never go down unless manually shut down. 149 00:12:16,530 --> 00:12:19,410 This has multiple advantages, including stability. 150 00:12:19,680 --> 00:12:26,780 If my router ID was originally ten 111 and the router reloaded, assuming that there were no loop backs 151 00:12:26,820 --> 00:12:31,020 enabled the router, id would have changed to ten 151. 152 00:12:31,260 --> 00:12:37,050 So there are two ID number could have changed, but with a loopback the router ID would remain as quadruple 153 00:12:37,050 --> 00:12:41,340 one as long as there were no other loopback configured on this router. 154 00:12:41,340 --> 00:12:44,580 So it doesn't matter what the physical interfaces are set to. 155 00:12:44,970 --> 00:12:53,940 It's recommended to set the router ID manually using this command and set it to a relevant loopback. 156 00:12:54,420 --> 00:12:58,380 In this case, I'm just going to set it to some arbitrary value to show you that you can. 157 00:12:58,380 --> 00:13:01,890 So I'm going to set it to 1921681.1. 158 00:13:02,730 --> 00:13:07,660 Which is not an IP address on my local router do show. 159 00:13:07,680 --> 00:13:14,010 IP protocol allows me to see that the router ID is 1921681.1. 160 00:13:14,670 --> 00:13:20,640 Now it's recommended practice to set the router ID to one of the loop backs on your router. 161 00:13:20,670 --> 00:13:23,790 So I'm going to set the router ID to quadruple one. 162 00:13:26,470 --> 00:13:30,310 As you can see here, the Rada ID is changed to quadruple one. 163 00:13:32,460 --> 00:13:39,230 The Hello packet then contains the hello and dead intervals, which must be the same on both routers. 164 00:13:39,240 --> 00:13:42,960 Otherwise, an adjacency or neighbor relationship will not be formed. 165 00:13:43,470 --> 00:13:47,970 It then contains the list of neighbors that thereafter knows about. 166 00:13:48,360 --> 00:13:54,750 That's how a router knows if there's two way communication, because it recognizes itself in the list 167 00:13:54,750 --> 00:13:57,990 of neighbors that it receives in the hello packet. 168 00:13:58,350 --> 00:14:03,000 It then contains the area ID, which must also match on both routers. 169 00:14:03,300 --> 00:14:09,450 It then contains a right of priority which can be used in designated router and backup designated router 170 00:14:09,450 --> 00:14:10,440 elections. 171 00:14:10,830 --> 00:14:17,880 It then contains the designated router or D or IP address backup designated router or BTR IP address. 172 00:14:18,270 --> 00:14:22,710 We're going to talk more about designated routers and backup designated routers in a moment. 173 00:14:23,220 --> 00:14:26,040 It then contains the authentication password. 174 00:14:26,100 --> 00:14:31,920 Now, there are various ways to set up authentication, including clear text and MD5 hashing. 175 00:14:32,340 --> 00:14:34,170 We'll talk more about those later. 176 00:14:34,470 --> 00:14:37,570 The authentication password needs to be the same. 177 00:14:37,590 --> 00:14:39,840 Otherwise, the relationship will not be formed. 178 00:14:40,230 --> 00:14:44,190 And then lastly, the stub area flag needs to be the same. 179 00:14:44,550 --> 00:14:50,400 The stub area flag denotes whether this is a stub area or a normal area. 180 00:14:50,760 --> 00:14:54,450 We'll talk more about stub areas once again in later slides.