Autonomous Systems. Entity that is independent from the rest, that works under its own rules solving its own problems. In terms of computing autonomous systems are applied in many processes, in this case will refer to networks of computers connected together.
Summary
[ hide ]
- 1 Concept
- 2 Characteristics of an AS
- 3 Independence of Autonomous Systems
- 4 Types
- 5 Sources
Concept
An Autonomous System (AS) is a group of networks or devices (routers) controlled by a single administrative authority for routing purposes, they can have their own policy for defining Internet paths.
Characteristics of an AS
An AS is a collection of networks and routing devices managed by a single organization.
Except at times of failure, an AS is connected (in a theoretical graph sense ); that is, there is a path between any pair of nodes .
Autonomous Systems communicate with each other through routers , they exchange information to update their routing tables through the BGP or EGP protocol and exchange Internet traffic that goes from one network to the other.
In turn, each Autonomous System is like a small Internet, since its role was carried out by a single entity, typically an Internet Service Provider (ISP) or a large organization with independent connections to multiple networks, which are they adhered to a single and clear policy of defining trajectories.
The ISP is an organization or Internet service provider that is in charge of giving autonomous systems IP addresses for the addressing and routing of their information . Even considering that the ISP could support multiple autonomous systems, the Internet only considers the path definition policy established by the ISP . Technically, an Autonomous System is defined as “a group of IP networks that have their own independent route policy”.
This definition refers to the fundamental characteristic of an Autonomous System: it carries out its own management of the traffic that flows between it and the other Autonomous Systems that make up the Internet . An AS or ASN number is assigned to each AS to be used by the BGP routing scheme, this number uniquely identifies each network within the Internet.
Independence of Autonomous Systems
Autonomous systems are given a number that identifies it as unique, this is a 16-bit integer, which allowed a maximum number of 65536 autonomous system assignments.
The Internet Assigned Numbers Authority ( IANA ) is in charge of assigning the numbers that identify it, together with the ISP, until now it had been assigned a range of private addresses from 64512 to 65534.
The ASN range from 56320 to 64511 and 65535 are reserved by the IANA and should not be used in any routable environment. ASN 0 can be used for non-routable networks
Types
Autonomous systems can be grouped into three categories, depending on their connections and mode of operation.
- SA stub – Connects only to a standalone system.
- Transit SA: it connects with several autonomous systems and also allows them to communicate with each other.
- SA multihomed: it connects with several autonomous systems, but does not support the transit traffic between them.
