1 00:00:00,240 --> 00:00:03,570 Open shortest path first or OSPF. 2 00:00:03,990 --> 00:00:10,380 OSPF is an industry standard powerful routing protocol used in many networking environments in the world 3 00:00:10,380 --> 00:00:11,010 today. 4 00:00:11,490 --> 00:00:14,340 The word open means that it's an open standard. 5 00:00:14,370 --> 00:00:19,200 This is a great advantage to using OSPF because of vendor interoperability. 6 00:00:19,320 --> 00:00:25,800 You can mix Cisco routers with Nortel Routers, HP routers and others and be assured that routes will 7 00:00:25,800 --> 00:00:28,560 be exchanged between the different vendors. 8 00:00:30,680 --> 00:00:39,230 Shortest path first or SBF, also known as the Dijkstra's algorithm, named after the developer who 9 00:00:39,230 --> 00:00:46,460 published the algorithm in 1959, is used by OSPF to determine the shortest path or best route to a 10 00:00:46,460 --> 00:00:47,420 destination. 11 00:00:47,960 --> 00:00:51,500 So what are we going to cover is firstly an overview of OSPF. 12 00:00:51,980 --> 00:00:53,900 Then we look at the features of OSPF. 13 00:00:53,930 --> 00:00:57,800 I'd like to show you how to set up a network using a single OSPF area. 14 00:00:58,190 --> 00:01:02,450 I'm going to show the importance of loopback and how they determine the router ID. 15 00:01:02,640 --> 00:01:09,860 You can look at quite a few configurations and setups in OSPF, including multiple area OSPF and authentication. 16 00:01:11,780 --> 00:01:19,820 OSPF once again is a link state routing protocol and will flood link state advertisements or listeners 17 00:01:20,570 --> 00:01:27,460 throughout the network or area describing firstly the links attached to a router. 18 00:01:27,470 --> 00:01:31,400 In other words, the radio interfaces and the state of those links. 19 00:01:31,640 --> 00:01:37,220 The state meaning a description of an interface and its relationship to neighboring routers. 20 00:01:37,370 --> 00:01:40,610 Is the interface up or is the interface done? 21 00:01:41,030 --> 00:01:46,940 That description would include, for example, the IP address of the interface, the subnet mask, the 22 00:01:46,940 --> 00:01:52,160 type of network to which it is connected, and the routers that are connected to that network and so 23 00:01:52,160 --> 00:01:52,820 forth. 24 00:01:54,040 --> 00:02:01,030 The collection of all of these link states forms the topological database or link state database. 25 00:02:01,960 --> 00:02:11,200 Radha has formed relationships by sending out hello messages using either multicast address 224005 or 26 00:02:11,200 --> 00:02:12,310 uni costs. 27 00:02:13,090 --> 00:02:18,940 LSA is once again flooded throughout the network or area and the link state database is created from 28 00:02:18,940 --> 00:02:25,960 these link state advertisements or Alice's OSPF once again uses the shortest path first algorithm or 29 00:02:25,960 --> 00:02:30,850 Dijkstra's algorithm to determine the best path to each destination. 30 00:02:32,020 --> 00:02:33,910 Now there's a bit of debate about this. 31 00:02:34,540 --> 00:02:40,960 Engineers will often discuss where in the Aussie model various protocols reside. 32 00:02:41,290 --> 00:02:44,950 OSPF resides directly on top of IP. 33 00:02:45,610 --> 00:02:51,820 OSPF does not use TCP or UDP for transporting of updates and information. 34 00:02:52,150 --> 00:02:55,510 It resides directly on top of IP. 35 00:02:56,360 --> 00:03:05,300 OSPF is referenced in the IP header with protocol ID 89, TCP is referenced with Protocol ID six and 36 00:03:05,300 --> 00:03:11,390 UDP Protocol ID 17, and thus some would debate that OSPF resides at layer four. 37 00:03:11,840 --> 00:03:18,830 For this course, however, we're going to say that OSPF resides at layer three directly on top of IP, 38 00:03:18,830 --> 00:03:20,270 also at layer three. 39 00:03:20,960 --> 00:03:27,200 For a lot of us in the real world, this isn't a major concern, but maybe from a theoretical point 40 00:03:27,200 --> 00:03:27,770 of view. 41 00:03:29,120 --> 00:03:29,510 Yes. 42 00:03:29,510 --> 00:03:30,860 A Wireshark capture. 43 00:03:32,050 --> 00:03:34,750 Showing various OSPF packets. 44 00:03:35,020 --> 00:03:42,250 So as an example, this first one is from a router with an IP address of ten 111 going to the well known 45 00:03:42,250 --> 00:03:46,540 multicast address for OSPF 224005. 46 00:03:47,160 --> 00:03:52,770 So that's the address used by OSPF for hellos on, for instance, an Ethernet segment. 47 00:03:53,570 --> 00:03:56,570 And you can see in the output here at layer two. 48 00:03:57,550 --> 00:04:00,400 We've got the sauce Mac address of the rudder. 49 00:04:01,640 --> 00:04:05,390 Sending information to an IP version for multicast address. 50 00:04:05,780 --> 00:04:08,270 In this case, the well known multicast address. 51 00:04:09,090 --> 00:04:10,320 For OSPF. 52 00:04:11,600 --> 00:04:17,600 At Layer two, the ether type is zero 800 in hexadecimal. 53 00:04:18,430 --> 00:04:20,529 In other words, referencing IP. 54 00:04:23,300 --> 00:04:24,370 At least three. 55 00:04:24,380 --> 00:04:31,040 We've got the source IP address once again of ten one one, one and destination of 224005. 56 00:04:33,890 --> 00:04:36,110 You can see this is an IP version for packet. 57 00:04:38,060 --> 00:04:47,030 And you can see here the protocol ID is OSPF in hexadecimal referenced as 0x59. 58 00:04:48,080 --> 00:04:51,860 Using a Windows calculator, we can set it to use hexadecimal. 59 00:04:51,890 --> 00:04:55,610 Set the value to 59 and then change it to decimal. 60 00:04:55,610 --> 00:04:58,850 And you can see the protocol ID is 89. 61 00:04:59,570 --> 00:05:04,850 So at layer three, OSPF is referenced with protocol ID 89. 62 00:05:05,480 --> 00:05:07,820 The source once again is ten 111. 63 00:05:07,850 --> 00:05:15,770 Destination is the multicast address for OSPF residing directly on top of IP is OSPF. 64 00:05:17,230 --> 00:05:20,650 So notice we have Ethernet IP OSPF. 65 00:05:20,680 --> 00:05:24,910 OSPF does not use TCP or UDP as a transport. 66 00:05:25,030 --> 00:05:26,500 It uses IP. 67 00:05:27,850 --> 00:05:29,470 You can see the OSPF header. 68 00:05:30,010 --> 00:05:32,080 It's version two of OSPF. 69 00:05:32,110 --> 00:05:34,000 You can see that this is a hello packet. 70 00:05:34,000 --> 00:05:35,500 In other words, type one. 71 00:05:37,390 --> 00:05:44,230 You can see it's four areas, zero OSPF areas can be referenced either as single decimal numbers like 72 00:05:44,230 --> 00:05:51,310 zero or in dotted IP decimal notation as in 0.0.0.0. 73 00:05:51,490 --> 00:05:54,400 It's like saying tomato or tomato. 74 00:05:54,640 --> 00:05:55,960 It's the same thing. 75 00:05:56,720 --> 00:05:58,850 You can see the source is ten 111. 76 00:06:00,530 --> 00:06:02,240 You can see it's a hello packet. 77 00:06:02,390 --> 00:06:06,440 His information like the network mosque, the hello interval. 78 00:06:07,720 --> 00:06:14,740 The root of priority, the root a date interval who the designated rata is, who the back of designated 79 00:06:14,740 --> 00:06:18,520 rata is, who the active neighbor is, and so forth. 80 00:06:18,550 --> 00:06:21,610 We're going to cover a lot of this information in the upcoming slides. 81 00:06:22,510 --> 00:06:24,370 The important thing to notice once again. 82 00:06:25,200 --> 00:06:29,160 Is that OSPF resides directly on top of IP. 83 00:06:29,430 --> 00:06:31,200 If we look at the next message. 84 00:06:32,310 --> 00:06:38,400 We're out at ten 112 is sending a database description to router ten 111. 85 00:06:39,180 --> 00:06:42,690 You'll see once again that there is no TCP or UDP. 86 00:06:43,690 --> 00:06:49,300 OSPF is referenced with protocol ID 89 in an IP version for header. 87 00:06:49,810 --> 00:06:52,930 OSPF for this course resides at layer three. 88 00:06:53,470 --> 00:06:57,460 But as mentioned, there's a bit of debate about exactly where it resides. 89 00:06:58,500 --> 00:07:00,630 Arata sends links that advertisements. 90 00:07:01,360 --> 00:07:07,450 To advertise the state of a link immediately when the state changes or periodically. 91 00:07:08,100 --> 00:07:13,350 By default, every 30 minutes the databases will be synchronized with the state of the links. 92 00:07:14,920 --> 00:07:20,830 OSPF routers from neighbor relationships and the list of neighbors is stored in the adjacency table 93 00:07:20,830 --> 00:07:22,660 or OSPF neighbor table. 94 00:07:23,960 --> 00:07:29,030 So topping the come on show IP OSPF neighbors will show you adjacent neighbors. 95 00:07:29,850 --> 00:07:38,910 OSPF uses multicast addresses 2 to 4 005 and 224006, which are link local multi costs. 96 00:07:39,240 --> 00:07:42,540 In other words, those multi costs cannot hop across a router. 97 00:07:43,020 --> 00:07:45,240 The riders have to be directly connected. 98 00:07:45,750 --> 00:07:52,170 OSPF will stall all routes learnt in the OSPF topology database or link state database. 99 00:07:53,210 --> 00:07:58,190 The link state database contains all routers and attached links in the area or network. 100 00:07:58,760 --> 00:08:02,990 All OSPF routers in the same area share the same database. 101 00:08:03,560 --> 00:08:08,600 Best routes are then put in to the writing table, also known as the forwarding table. 102 00:08:09,920 --> 00:08:12,320 There are various packet types used in OSPF. 103 00:08:12,920 --> 00:08:19,460 The first type is a hello packet, which is used firstly to dynamically discover neighbours and secondly 104 00:08:19,460 --> 00:08:23,090 to form neighbour relationships and maintain those neighbour relationships. 105 00:08:23,600 --> 00:08:30,410 There are some default intervals for hellos on broadcast multimedia segments such as Ethernet. 106 00:08:30,560 --> 00:08:32,630 The interval is 10 seconds. 107 00:08:33,169 --> 00:08:38,870 The second default interval is 30 seconds, which is used on non broadcast segments such as serial links 108 00:08:38,870 --> 00:08:44,870 and may non broadcast multi axis environments such as frame relay. 109 00:08:45,890 --> 00:08:52,130 OSPF has what's called a dead interval or dead timer, which is four times the interval by default. 110 00:08:52,430 --> 00:08:58,010 If you change the hollow interval, OSPF will automatically change the debt interval to a value four 111 00:08:58,010 --> 00:09:01,520 times the hello interval on a specific interface. 112 00:09:01,940 --> 00:09:04,310 So how those are used to discover neighbors? 113 00:09:04,310 --> 00:09:10,250 And if a hello is not received within the date interval, the neighbor relationship is torn down because 114 00:09:10,250 --> 00:09:13,250 it's deemed that the neighbor is no longer available. 115 00:09:14,270 --> 00:09:18,140 The second type of packet is what's called a database description. 116 00:09:18,590 --> 00:09:25,850 Written is d, d, 0dd, which is used to exchange brief versions of each linked state. 117 00:09:25,850 --> 00:09:26,810 Advertisement. 118 00:09:27,080 --> 00:09:33,530 OSPF is a link state routing protocol routers exchange information about the state of links through 119 00:09:33,530 --> 00:09:34,940 link state advertisements. 120 00:09:34,940 --> 00:09:41,720 When an initial relationship is formed between two OSPF routers, they will exchange database descriptions, 121 00:09:41,720 --> 00:09:45,170 giving each other an overview of what the database contains. 122 00:09:45,650 --> 00:09:52,820 If parts of the database are missing on one router, it will send a link state request requesting full 123 00:09:52,910 --> 00:09:55,550 LSA information from the neighboring router. 124 00:09:55,940 --> 00:10:01,610 The neighboring router will send what's called a link state update, which is a packet that contains 125 00:10:01,610 --> 00:10:07,400 links, state advertisements and as mentioned, is typically sent in response to a link state request. 126 00:10:07,520 --> 00:10:13,730 This contains detailed information about the link state database rather than just an overview of it 127 00:10:13,730 --> 00:10:16,100 which was contained in the database description. 128 00:10:17,180 --> 00:10:22,970 Links that acknowledgments acknowledge or confirm receipt of a link state update message.