Routing Part 2

Routing

Autonomous System (AS)

a network under the administrative control of one organization

stub AS

have a connection to only one other AS and carry their own traffic

Multi-homed AS

have connections to multiple other ASes but only carry their own traffic

Transit ASes

have connections to multiple other ASes and carry traffic locally and between the ASes they are connected to

provider-customer

one AS is paid by another for handling traffic

peering

two ASes view themselves as equal in terms of volume of traffic and provide access to each other’s customers without payment

tier 1 provider

backbone of internet, peer with each other and provide transit to providers at the lower tiers

tier 2 provider

peer with each other, buy transit from tier 1 providers and provide transit to tier 3 providers

tier 3 providers

buy transit from tier 1 and 2 providers

Gao-Rexford rules

routes received from customers are advertised to everyone, routes received from peers and providers are only advertised to customers

Gao-Rexford rule guarantees

routes are valley free, all ASes are reachable, BGP speakers will all converge