Multihoming means connecting your AS to multiple upstreams. It provides redundancy and traffic engineering.
Types:
Single router, multiple links. One router connects to ISPs.
Multiple routers, multiple links. Each ISP connects to different router.
Diverse paths. Links enter different buildings or cities.
Requirements:
- Your own ASN
- Provider-independent IP space
- BGP configuration on your routers
Without BGP: You can multihome using static routes, but failover is manual.