／var／logmarcus chiu

Autonomous System (AS) - Domain

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Autonomous System (AS) or Domain
  • is a collection of networks or subnets that are in the same administrative domain

Autonomous System Number (ASN)

each AS is assigned an Autonomous System Number (ASN) a 16-bit integer by the Internet Network Information Center (InterNIC)

its 16-bit number are used in IP GLOP addresses

ASNs were just 16-bit numbers, but are now 32-bit numbers (because the internet grew to the point of running out of the 65,536 or 2^16 initial allocation)

Autonomous System & Network Protocols

each AS is composed of routers that have 2 goals:

Autonomous System Types

AS Types

Description

Example

Non-Transit AS (Subscriber AS)

an AS does not let transit traffic from another AS pass through itself

types of Non-Transit AS:

  • Stub AS - an AS connected to only one other AS
  • Multi-Homed AS - an AS connected to more than one other AS
  • Stub AS - a corporate network that is connected to an AS is considered to have the same AS number as the AS it is connected to
  • Multi-Homed AS - corporate network with several Internet connections to different ISPs

Transit AS (Provider)

an AS connected to more than one other AS and can be used for transit traffic between autonomous systems

types of Transit AS:

  • Direct Transit AS - directly connected to subscribers
  • Indirect Transit AS - connected to other providers, not directly connected to subscribers
  • Direct Transit AS - They are usually administered by large Internet service providers (ISPs)
  • Indirect Transit AS - backbone networks

Autonomous System Relationships & Policies

AS Relationships & Policies

Description

Provider-Customer
  • providers connects customers to internet
  • customer maybe a corporation or smaller ISP
  • common policy is to advertise
    • all routes I know to my customer
    • routes learned from customers to everyone

Customer-Provider
  • the other direction of Provider-Customer
  • customer wants
    • to get traffic directed to him by his provider
    • to be able to send traffic to the rest of the Internet through his provider
  • common policy is to
    • advertise own prefixes and routes learned from own customers to provider
    • but don’t advertise routes learned from one provider to another

Peer
  • is symmetrical peering between autonomous systems
  • 2 providers can get access to each other’s customers without having to pay another provider
  • common policy
    • advertise routes learned from own customers to peer
    • advertise routes from peer to own customers
    • but don’t advertise routes from peer to any provider or vice versa