A collection of IP networks and routers under the control of one administrative entity.
- Identified by a unique AS Number (ASN), assigned by IANA.
- Contains multiple routers and uplinks to other ASes.
- The boundary between AS domains defines the boundary between Intra-AS and Inter-AS routing.
Routing
Intra-AS
Also known as Interior Gateway Protocol (IGP). Operates within a single AS.
Inter-AS
Also known as Exterior Gateway Protocol (EGP). Operates between different ASes.
| Scope | Principle | Protocols |
|---|---|---|
| Intra-AS | Distance Vector | RIP |
| Intra-AS | Link State | OSPF, IS-IS |
| Inter-AS | Path Vector | BGP |
See Routing for algorithm details.
