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These are the user uploaded subtitles that are being translated: 1 00:00:00,000 --> 00:00:05,000 align:middle line:84% Link state routing protocols such as OSPF 2 00:00:05,000 --> 00:00:12,000 align:middle line:84% allow for the division of large Autonomous System into smaller groupings called areas. 3 00:00:12,000 --> 00:00:14,000 align:middle line:84% In this example, we have a RIP router 4 00:00:14,000 --> 00:00:19,000 align:middle line:84% connected to a router running both RIP and OSPF 5 00:00:19,000 --> 00:00:23,000 align:middle line:84% so RIP is connected to an OSPF Autonomous System. 6 00:00:23,000 --> 00:00:28,000 align:middle line:84% The routers within OSPF are under common administrative domain 7 00:00:28,000 --> 00:00:32,000 align:middle line:84% in other words, they are part of the Autonomous System. 8 00:00:32,000 --> 00:00:34,000 align:middle line:84% The OSPF Autonomous System however 9 00:00:34,000 --> 00:00:40,000 align:middle line:84% can be broken up into multiple areas to allow for smaller routing tables 10 00:00:40,000 --> 00:00:44,000 align:middle line:84% reduction of flooding of link state advertisements 11 00:00:44,000 --> 00:00:49,000 align:middle line:84% rank summarization and more efficient use of resources. 12 00:00:49,000 --> 00:00:55,000 align:middle line:84% If you have many routers in a single area, the routing tables of those routers 13 00:00:55,000 --> 00:01:02,000 align:middle line:84% can get very large, so this allows for the reduction of routing tables on certain routers 14 00:01:02,000 --> 00:01:09,000 align:middle line:84% by breaking the Autonomous System into a hierarchical design with multiple areas. 15 00:01:09,000 --> 00:01:15,000 align:middle line:84% In OSPF, these routers are known as Area Border Routers or ABRs 16 00:01:15,000 --> 00:01:18,000 align:middle line:84% they have interfaces in multiple areas. 17 00:01:18,000 --> 00:01:24,000 align:middle line:84% These routers are known as internal routers as they are only part of a single area 18 00:01:24,000 --> 00:01:28,000 align:middle line:84% they have no interfaces in any other areas. 19 00:01:28,000 --> 00:01:35,000 align:middle line:84% This router is known as an Autonomous System border router as it connects OSPF 20 00:01:35,000 --> 00:01:40,000 align:middle line:84% to an external Autonomous System or routing process which in this case is RIP. 21 00:01:40,000 --> 00:01:42,000 align:middle line:84% These routers are known as backbone routers 22 00:01:42,000 --> 00:01:45,000 align:middle line:84% and they also called internal routers. 23 00:01:45,000 --> 00:01:48,000 align:middle line:84% They are internal to the backbone area. 24 00:01:48,000 --> 00:01:53,000 align:middle line:84% one of the advantages of creating multiple areas is that 25 00:01:53,000 --> 00:01:59,000 align:middle line:84% link changes within 1 area are hidden from other routers in other areas 26 00:01:59,000 --> 00:02:06,000 align:middle line:84% so within OSPF if we had network 10.1.1.0 in area 1 27 00:02:06,000 --> 00:02:13,000 align:middle line:84% and that network went down that information will be hidden from routers in other areas. 28 00:02:13,000 --> 00:02:17,000 align:middle line:84% They wouldn’t have to rerun the SPF algorithm 29 00:02:17,000 --> 00:02:21,000 align:middle line:84% because they're unaware of that network going down. 30 00:02:21,000 --> 00:02:29,000 align:middle line:84% so this router in area 2 and this router in are 3 will not be aware of that fact 31 00:02:29,000 --> 00:02:32,000 align:middle line:84% that network 10.1.1.0 has gone down 32 00:02:32,000 --> 00:02:35,000 align:middle line:84% you can do this by configuring area 2 33 00:02:35,000 --> 00:02:40,000 align:middle line:84% and area 3 as what are called stub and totally stubby areas. 34 00:02:40,000 --> 00:02:44,000 align:middle line:84% You can also use route summarization to reduce 35 00:02:44,000 --> 00:02:50,000 align:middle line:84% the need to rerun the SPF algorithm when a network goes down. 36 00:02:50,000 --> 00:02:54,000 align:middle line:84% The idea here is to use your resources more efficiently 37 00:02:54,000 --> 00:02:58,000 align:middle line:84% by reducing the flooding of link state advertisements. 38 00:02:58,000 --> 00:03:05,000 align:middle line:84% Links state advertisements within area 1 are contained within that area 39 00:03:05,000 --> 00:03:11,000 align:middle line:84% or limited to that area and summary LSAs propagated to other areas. 40 00:03:11,000 --> 00:03:17,000 align:middle line:84% These summary LSAs are blocked by Area Border of Routers or ABRs 41 00:03:17,000 --> 00:03:20,000 align:middle line:84% so they don’t go into other areas such as area 2. 42 00:03:20,000 --> 00:03:26,000 align:middle line:84% So routers in area 2 are unaware of specific routes in area 1. 43 00:03:26,000 --> 00:03:30,000 align:middle line:84% To enable connectivity a summary route 44 00:03:30,000 --> 00:03:35,000 align:middle line:84% or default route can be propagated into area 2. 5379