interdomain

Interdomain refers to interactions across different administrative domains, such as autonomous systems on the Internet. In networking, interdomain routing is the process of exchanging reachability information between these domains to enable global Internet routing.

The Border Gateway Protocol (BGP) is the de facto interdomain routing protocol, designed to run over TCP and exchange reachability announcements between neighboring autonomous systems. Each route carries attributes, including AS_PATH, NEXT_HOP, and policy-related attributes like LOCAL_PREF and MULTI_EXIT_DISC. Routing decisions are policy-driven rather than purely shortest-path; operators filter prefixes, apply local preferences, and may manipulate announcements to influence path selection. Routes are learned from peers (eBGP) or customers (iBGP) and may be aggregated or redistributed into other protocols.

The interdomain system is decentralized, with connections established through customer-provider, peer-to-peer, or transit arrangements, and often facilitated by Internet Exchange Points (IXPs). To scale the global routing table, techniques like route reflectors and BGP confederations are used. Interdomain traffic engineering uses BGP attributes to influence path selection and traffic flows.

Security is a major concern in interdomain routing because BGP lacks built-in authentication, leaving the system vulnerable to misconfigurations and attacks such as prefix hijacking. Mitigations include RPKI-based route validation, BGPsec, prefix filtering, and careful peering policy.

Beyond networking, the term interdomain can refer to cross-domain collaboration, inter-organizational data exchange, or inter-domain security architectures, but in computing it most commonly denotes interdomain routing on the Internet.