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Routing & Switching · Intermediate

BGP Multihoming

Connecting an AS to two or more upstream links or providers using BGP for redundancy and traffic control.

Definition

Designs range from dual links to one ISP to dual-homed to two ISPs. Outbound traffic is controlled with local preference or weight, inbound with AS-path prepending, MED or ISP communities. Provider-independent address space and a public ASN are typically needed for multi-provider multihoming.

Example

Two ISPs advertise default routes; local preference 200 makes ISP1 primary.

Exam tip

Know which tools control inbound vs outbound traffic in multihomed designs.

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