About Peering

Peering is when two networks (Autonomous Systems) agree to connect directly to each other and exchange routing information to carry traffic between themselves, rather than relying on an upstream transit provider. [1]

Each party in a peering relationship will configure their routers to announce to connected neighbouring routers (peers) the IP address subnets that it has routes for, for example those belonging to the customers of an ISP or hosting company, so that peers know where to direct any traffic for those subnets that it receives.

When a router receives and accepts a route announcement from one of its peers, it will then store an entry in its routing table. [2]

A routing table, in its simplest form, records which interfaces / gateways are able to route IP traffic onwards, and a cost metric to be used in prioritising routes, where there are multiple paths to a destination network.