Original subtitles

1

Some terms that you will need to understand with regards to routing protocols

2

include Autonomous System, Interior Gateway Protocol or Internal Gateway Protocol

3

eExterior Gateway Protocol or External Gateway Protocol.

4

The first term AS or Autonomous System is a grouping of networks

5

under a single administrative domain

6

in other words, the routers within an autonomous system

7

such as AS 1 are under the control of a group of people or a company

8

as an example, this autonomous system on the left could be Coke's Autonomous System

9

this autonomous system could be Pepsi’s Autonomous System

10

it's very unlikely that Coke are going to allow Pepsi to manage their network

11

or that Pepsi are going to allow Coke to manage their network.

12

They are separate autonomous systems under different people's control

13

or different administrative control or under a different companies control

14

routers in the Coke AS are under the control of Coca-Cola Employees

15

rather than Pepsi Employees, this is a separate Autonomous System

16

various interior or Internal Gateway Protocols or IGPs

17

can be used within an Autonomous System

18

example would include RIP, EIGRP, OSPF and ISIS.

19

EGPs or Exterior Gateway Protocols are used between Autonomous Systems.

20

The EGP that’s in used today between autonomous system is BGP or Border Gateway Protocol.

21

So if this autonomous system was a Company that needed to connect to the Internet

22

they would connect to their ISP or Internet Service Provider using BGP

23

within the Autonomous System, they may be using OSPF

24

as the Interior Gateway Protocol but BGP is the protocol used

25

between their Autonomous Systems and the ISP

26

they will be learning about Internet routes through BGP.

27

Now only very large companies generally run BGP

28

and receive routes from their ISP using BGP.

29

however, ISP’s which carry routes of customers in the Internet run BGP.

30

So we may have an ISP on the left-hand side

31

and an ISP on the right-hand side

32

and they would be running BGP between them.

33

internally in their Autonomous Systems

34

or AS's they may be running different routing protocols.

35

so as an example, OSPF could be used in autonomous system 1

36

and ISIS could be used in Autonomous System 2.

37

Each ISP determines which routing protocol to use internally

38

but they connect to one another using BGP.

39

Now autonomous systems are registered numbers

40

in a similar way to IP addresses on the Internet.

41

You can't just use any autonomous system when connecting to the Internet.

42

so before you connect to the Internet using BGP

43

you would register an Autonomous System number.

44

There are private Autonomous System numbers that can be used without registration

45

so within an Autonomous System you could use a private AS number

46

or you could use any other number as long as you're not connecting to the Internet

47

but as soon as you connect to the Internet

48

you will need to use a publicly registered Autonomous System number

49

or an Autonomous System number allocated to you by your ISP.

50

Now this wouldn’t apply to you if you're using static routes

51

or once again if a private Autonomous System number has been allocated to you by your ISP

52

but for very large networks or if you want to create your own Internet Service Provider

53

the Autonomous System number that you use will need to be registered.