1 00:00:00,300 --> 00:00:08,790 Open shortest path first or OSPF OSPF is an industry standard powerful writing protocol used in many 2 00:00:08,790 --> 00:00:14,620 networking environments in the world today the word open means that it's an open standard. 3 00:00:14,640 --> 00:00:19,470 This is a great advantage to using OSPF because of Vendy interoperability. 4 00:00:19,590 --> 00:00:26,010 You can make Cisco routers with Nortel routers HP routers and others and be assured that rats will be 5 00:00:26,010 --> 00:00:28,600 exchanged between the different vendors. 6 00:00:30,810 --> 00:00:39,960 Showed us both first or SBF also known as the digesters algorithm named after the developer who published 7 00:00:39,960 --> 00:00:47,750 the algorithm in 1959 is used by SPF to determine the shortest path or best route to a destination. 8 00:00:48,180 --> 00:00:49,660 So are we going to cover these. 9 00:00:49,660 --> 00:00:52,150 Firstly an overview of OSPF. 10 00:00:52,200 --> 00:00:54,050 We look at the features of OSPF. 11 00:00:54,090 --> 00:00:58,350 I'd like to show you how to set up a network using a single OSPF area. 12 00:00:58,350 --> 00:01:02,550 I'm going to show the importance of packs and how they determine the Rodda ID. 13 00:01:02,650 --> 00:01:09,720 We look at quite a few configurations and set ups in OSPF including multiple area OSPF and authentication 14 00:01:11,880 --> 00:01:19,650 OSPF once again is a link state routing protocol and will flood links that advertizements or elysées 15 00:01:20,760 --> 00:01:23,250 throughout the network or area. 16 00:01:23,430 --> 00:01:27,530 Describing Firstly the links attached to a router. 17 00:01:27,660 --> 00:01:34,110 In other words the router interfaces and the state of those links the state meaning a description of 18 00:01:34,110 --> 00:01:41,170 an interface and its relationship to neighboring routers is the interface up or is the interface down. 19 00:01:41,220 --> 00:01:47,430 That description would include for example the IP address of the interface the subnet mask the top of 20 00:01:47,430 --> 00:01:52,840 network to which it is connected and the routers that are connected to that network and so forth. 21 00:01:54,190 --> 00:02:00,910 The collection of all of these links states forms the top alogical database all links state database 22 00:02:02,150 --> 00:02:10,400 routing form relationships by sending out Hello messages using either multicast address 2 2 4 0 0 5 23 00:02:11,060 --> 00:02:18,240 0 unique costs Elisei is once again a flooded throughout the network area and the link state database 24 00:02:18,240 --> 00:02:22,200 is created from these links to advertisements or elysées. 25 00:02:22,310 --> 00:02:28,400 Always be if once again uses the shortest path first algorithm or digesters algorithm to determine the 26 00:02:28,400 --> 00:02:30,970 best path to each destination. 27 00:02:32,210 --> 00:02:34,730 Now there's a bit of debate about this. 28 00:02:34,730 --> 00:02:44,060 Engineers will often discuss where in the model various protocols reside OSPF resides directly on top 29 00:02:44,060 --> 00:02:53,930 of IP OSPF does not use TCAP or UDP for transporting of updates and information it resides directly 30 00:02:54,200 --> 00:03:04,250 on top of IP always is referenced in the IP header with protocol ID 89 TZP reference with protocol IDs 31 00:03:04,270 --> 00:03:11,600 6 and UDP protocol ID 17 and thus some would debate that OSPF resides at Layer 4. 32 00:03:11,970 --> 00:03:19,020 For this cause however we are going to say that OSPF resides a layer 3 directly on top of IP. 33 00:03:19,060 --> 00:03:23,130 Also at least three for a lot of us in the real world. 34 00:03:23,160 --> 00:03:25,290 This isn't a major concern. 35 00:03:25,620 --> 00:03:27,810 That may be from a theoretical point of view. 36 00:03:29,320 --> 00:03:35,210 Yes why is Shaw capture showing various OSPF packets. 37 00:03:35,240 --> 00:03:42,980 Says an example the first one is from Iraq with an IP address of 10 1 1 1 Going to the well-known multicast 38 00:03:42,980 --> 00:03:47,270 address for OSPF 2 2 4 0 0 5. 39 00:03:47,380 --> 00:03:54,390 So that's the address used by always be a follows on for instance an Ethernet segment and you can see 40 00:03:54,390 --> 00:03:57,510 in the output here at Layer 2. 41 00:03:57,740 --> 00:04:05,930 We've got the source MAC address of the Rodda sending information to an IP version 4 multicast address. 42 00:04:05,980 --> 00:04:18,620 In this case the well-known multicast address V.F. Atlay to the ether type is 0 800 in hexadecimal. 43 00:04:18,650 --> 00:04:20,420 In other words referencing IP 44 00:04:23,350 --> 00:04:30,450 at least three we've got the source IP address once again of 10 1 1 1 and this a nation of 2 2 4 0 0 45 00:04:30,450 --> 00:04:30,900 46 00:04:34,020 --> 00:04:43,590 you can see this as an IP version for packet and you can see here the protocol ID is OSPF in hexadecimal 47 00:04:43,680 --> 00:04:49,940 referenced as 0 x 5 9 using a Windows calculator. 48 00:04:50,160 --> 00:04:56,490 We can set it to use hexadecimal set the value to 59 and then change it to decimal and you can see the 49 00:04:56,490 --> 00:04:59,280 protocol ID is 89. 50 00:04:59,820 --> 00:05:08,970 So at least three OSPF is referenced with protocol ID 89 the source once again is 10 1 on 1 destination 51 00:05:09,240 --> 00:05:18,650 is the multi-course address for OSPF residing directly on top of IP is OSPF So notice we have ethernet 52 00:05:19,010 --> 00:05:25,100 IP OSPF OSPF does not use TCAP or UDP as a transport. 53 00:05:25,190 --> 00:05:27,850 It uses IP. 54 00:05:28,040 --> 00:05:34,100 You can see the OSPF header version 2 of OSPF you can see that this is a hollow packet. 55 00:05:34,100 --> 00:05:43,250 In other words type 1 you can see it's for areas 0 0 SBF areas can be referenced either a single decimal 56 00:05:43,250 --> 00:05:51,430 numbers like 0 or in dotted IP decimal notation as in 0.0 0.0. 57 00:05:51,710 --> 00:05:54,670 It's like saying tomorrow or tomato. 58 00:05:54,830 --> 00:05:56,710 It's the same thing. 59 00:05:56,910 --> 00:06:04,410 You can see the sources 10 1 1 1 you can see it's a hollow packet is information like that network mosque 60 00:06:05,080 --> 00:06:13,890 the hollow interval the route of priority the route a date interval to the designated route is to the 61 00:06:13,890 --> 00:06:20,390 backup designator Audi's who the active neighbors and so forth we're going to cover a lot of this information 62 00:06:20,390 --> 00:06:28,300 in the upcoming sleights the important thing to notice once again is that OSPF resides directly on top 63 00:06:28,300 --> 00:06:29,610 of IP. 64 00:06:29,650 --> 00:06:37,060 If you look at the next message where rodded 10 1 1 2 is sending a database description to route it 65 00:06:37,090 --> 00:06:46,640 10 1 1 1 you'll see once again that there is no TZP UDP OSPF is referenced with particle ID. 66 00:06:46,790 --> 00:06:53,440 89 in an IP version 4 header always be it for this course resides at least three. 67 00:06:53,570 --> 00:06:57,520 But as mentioned there's a bit of debate about exactly where it resides. 68 00:06:58,620 --> 00:07:05,030 ARADAS sends links that advertizements to advertise the state of the link immediately when the state 69 00:07:05,030 --> 00:07:10,300 changes or periodically by default every 30 minutes. 70 00:07:10,330 --> 00:07:17,310 The databases will be synchronized with the state of the links always be of routers or neighbor relationships 71 00:07:17,870 --> 00:07:24,740 and the list of neighbors is stored in the adjacency table or OSPF neighbor table so topping that come 72 00:07:24,740 --> 00:07:33,420 on show the OSPF neighbors will show you adjacent neighbors always uses multicast addresses 2 2 4 0 73 00:07:33,430 --> 00:07:39,420 0 5 and 2 2 4 0 0 6 which are link local multicast. 74 00:07:39,430 --> 00:07:42,800 In other words those multicast cannot hop across a router. 75 00:07:43,210 --> 00:07:50,260 The writers have to be directly connected always fearful store all routes learnt in the OSPF typology 76 00:07:50,260 --> 00:07:53,210 database or link state database. 77 00:07:53,320 --> 00:07:59,490 The links state database contains all routers and attach links in the area or network will always be 78 00:07:59,490 --> 00:08:01,200 of routers in the same area. 79 00:08:01,530 --> 00:08:03,520 Share the same database. 80 00:08:03,690 --> 00:08:09,920 Best routes are then put into the writing table also known as the forwarding table. 81 00:08:09,950 --> 00:08:12,830 There are various packet types used in OSPF. 82 00:08:13,020 --> 00:08:19,530 The first type is a hollow packet which is used firstly to dynamically discover neighbors and secondly 83 00:08:19,530 --> 00:08:23,620 to form neighbor relationships and maintain those neighbor relationships. 84 00:08:23,650 --> 00:08:30,790 There are some default intervals for halos on broadcast multimedia segments such as Ethernet. 85 00:08:30,810 --> 00:08:33,140 The interval is 10 seconds. 86 00:08:33,270 --> 00:08:38,910 The second default interval is 30 seconds which is used on non-broadcast segments such a serial links 87 00:08:39,030 --> 00:08:47,570 an MBA made non-broadcast multi-axis environments such as Frame Relay always has what's called a data 88 00:08:47,570 --> 00:08:52,510 interval or dead timer which is four times the interval by default. 89 00:08:52,680 --> 00:08:58,600 If you change the hollow interval I was fearful automatically change the date interval to value 4 times 90 00:08:58,610 --> 00:09:05,400 the hello interval on a specific interface so hello are used to discover neighbors and if a hello is 91 00:09:05,400 --> 00:09:11,130 not received within the data interval the neighbor relationship is torn down because it's deemed that 92 00:09:11,130 --> 00:09:14,380 the labor is no longer available. 93 00:09:14,430 --> 00:09:22,590 The second top of packet is what's called a database description written as DD or dbd which is used 94 00:09:22,800 --> 00:09:30,410 to exchange brief versions of each link state advertisement OSPF as a link state routing protocol routers 95 00:09:30,420 --> 00:09:35,050 exchange information about the state of links to link state advertisements. 96 00:09:35,130 --> 00:09:41,580 When an initial relationship is formed between two SPF routers they will exchange database descriptions 97 00:09:41,940 --> 00:09:45,430 giving each other an overview of what the database contains. 98 00:09:45,810 --> 00:09:52,690 If parts of the database are missing on one router it will send a link state request requesting fool 99 00:09:53,070 --> 00:09:57,990 alla same formation mation from the neighboring router the neighboring router will send what's called 100 00:09:58,050 --> 00:10:05,040 a link State Update which is a packet that contains links state advertisements and as mentioned is typically 101 00:10:05,040 --> 00:10:07,780 sent in response to a linked state request. 102 00:10:07,800 --> 00:10:13,650 This contains detailed information about the link state database rather than just an overview of it 103 00:10:13,950 --> 00:10:16,120 which was contained in the database description. 104 00:10:17,340 --> 00:10:22,890 Links state acknowledgements acknowledge or confirm receipt of the link state update message.