1 00:00:00,000 --> 00:00:06,000 Some terms that you will need to understand with regards to routing protocols 2 00:00:06,000 --> 00:00:14,000 include Autonomous System, Interior Gateway Protocol or Internal Gateway Protocol 3 00:00:14,000 --> 00:00:18,000 eExterior Gateway Protocol or External Gateway Protocol. 4 00:00:18,000 --> 00:00:25,000 The first term AS or Autonomous System is a grouping of networks 5 00:00:25,000 --> 00:00:28,000 under a single administrative domain 6 00:00:28,000 --> 00:00:31,000 in other words, the routers within an autonomous system 7 00:00:31,000 --> 00:00:39,000 such as AS 1 are under the control of a group of people or a company 8 00:00:39,000 --> 00:00:44,000 as an example, this autonomous system on the left could be Coke's Autonomous System 9 00:00:44,000 --> 00:00:48,000 this autonomous system could be Pepsi’s Autonomous System 10 00:00:48,000 --> 00:00:54,000 it's very unlikely that Coke are going to allow Pepsi to manage their network 11 00:00:54,000 --> 00:00:58,000 or that Pepsi are going to allow Coke to manage their network. 12 00:00:58,000 --> 00:01:03,000 They are separate autonomous systems under different people's control 13 00:01:03,000 --> 00:01:10,000 or different administrative control or under a different companies control 14 00:01:10,000 --> 00:01:16,000 routers in the Coke AS are under the control of Coca-Cola Employees 15 00:01:16,000 --> 00:01:20,000 rather than Pepsi Employees, this is a separate Autonomous System 16 00:01:20,000 --> 00:01:26,000 various interior or Internal Gateway Protocols or IGPs 17 00:01:26,000 --> 00:01:30,000 can be used within an Autonomous System 18 00:01:30,000 --> 00:01:36,000 example would include RIP, EIGRP, OSPF and ISIS. 19 00:01:36,000 --> 00:01:42,000 EGPs or Exterior Gateway Protocols are used between Autonomous Systems. 20 00:01:42,000 --> 00:01:50,000 The EGP that’s in used today between autonomous system is BGP or Border Gateway Protocol. 21 00:01:50,000 --> 00:01:57,000 So if this autonomous system was a Company that needed to connect to the Internet 22 00:01:57,000 --> 00:02:02,000 they would connect to their ISP or Internet Service Provider using BGP 23 00:02:02,000 --> 00:02:07,000 within the Autonomous System, they may be using OSPF 24 00:02:07,000 --> 00:02:12,000 as the Interior Gateway Protocol but BGP is the protocol used 25 00:02:12,000 --> 00:02:16,000 between their Autonomous Systems and the ISP 26 00:02:16,000 --> 00:02:20,000 they will be learning about Internet routes through BGP. 27 00:02:20,000 --> 00:02:25,000 Now only very large companies generally run BGP 28 00:02:25,000 --> 00:02:29,000 and receive routes from their ISP using BGP. 29 00:02:29,000 --> 00:02:35,000 however, ISP’s which carry routes of customers in the Internet run BGP. 30 00:02:35,000 --> 00:02:39,000 So we may have an ISP on the left-hand side 31 00:02:39,000 --> 00:02:41,000 and an ISP on the right-hand side 32 00:02:41,000 --> 00:02:43,000 and they would be running BGP between them. 33 00:02:43,000 --> 00:02:47,000 internally in their Autonomous Systems 34 00:02:47,000 --> 00:02:51,000 or AS's they may be running different routing protocols. 35 00:02:51,000 --> 00:02:55,000 so as an example, OSPF could be used in autonomous system 1 36 00:02:55,000 --> 00:02:59,000 and ISIS could be used in Autonomous System 2. 37 00:02:59,000 --> 00:03:05,000 Each ISP determines which routing protocol to use internally 38 00:03:05,000 --> 00:03:09,000 but they connect to one another using BGP. 39 00:03:09,000 --> 00:03:13,000 Now autonomous systems are registered numbers 40 00:03:13,000 --> 00:03:17,000 in a similar way to IP addresses on the Internet. 41 00:03:17,000 --> 00:03:23,000 You can't just use any autonomous system when connecting to the Internet. 42 00:03:23,000 --> 00:03:26,000 so before you connect to the Internet using BGP 43 00:03:26,000 --> 00:03:30,000 you would register an Autonomous System number. 44 00:03:30,000 --> 00:03:36,000 There are private Autonomous System numbers that can be used without registration 45 00:03:36,000 --> 00:03:41,000 so within an Autonomous System you could use a private AS number 46 00:03:41,000 --> 00:03:46,000 or you could use any other number as long as you're not connecting to the Internet 47 00:03:46,000 --> 00:03:48,000 but as soon as you connect to the Internet 48 00:03:48,000 --> 00:03:52,000 you will need to use a publicly registered Autonomous System number 49 00:03:52,000 --> 00:03:58,000 or an Autonomous System number allocated to you by your ISP. 50 00:03:58,000 --> 00:04:02,000 Now this wouldn’t apply to you if you're using static routes 51 00:04:02,000 --> 00:04:10,000 or once again if a private Autonomous System number has been allocated to you by your ISP 52 00:04:10,000 --> 00:04:16,000 but for very large networks or if you want to create your own Internet Service Provider 53 00:04:16,000 --> 00:04:21,000 the Autonomous System number that you use will need to be registered.