multihomed

Multihomed refers to a network, site, or organization that is connected to more than one Internet service provider (ISP). The primary purpose is redundancy and reliability, ensuring continued connectivity even if one link or ISP fails. Multihoming can also improve bandwidth availability and, in some cases, influence inbound traffic patterns and performance.

The common technical approach is to use the Border Gateway Protocol (BGP) to advertise the network’s IP prefixes to all connected providers. A multihomed organization typically uses a unique Autonomous System Number (ASN) and public IP address space obtained from a regional Internet registry. This allows the network to control routing policies, select preferred paths, and perform traffic engineering. In practice, outbound traffic is routed according to defined policies and path attributes, while inbound traffic is influenced by how providers announce the prefixes and how routes are learned across the Internet. Smaller networks may rely on managed services or provider-provided multihoming options that abstract some of the BGP complexity.

Benefits of multihoming include improved fault tolerance, reduced risk of outage, potential performance improvements, and greater control over routing. Drawbacks include higher cost, increased operational complexity, and the need for specialized expertise to configure and maintain BGP sessions, filter routes, and monitor for anomalies. Security considerations are also important, as improper BGP configuration can lead to route leaks or hijacks, so deployments typically include strict prefix filtering and monitoring.

Multihoming is commonly used by enterprises, data centers, campuses, and hosting providers to secure reliable Internet connectivity and to optimize traffic inflows and outflows across multiple carriers.