Multihoming
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Multihoming is the practice of connecting a host or a computer network to more than one network. This can be done in order to increase reliability or performance. A typical host or end-user network is connected to just one network. Connecting to multiple networks can increase reliability because if one connection fails, packets can still be routed through the remaining connection(s). Connecting to multiple networks can also improve performance because data can be transmitted and received through the multiple connections simultaneously, multiplying throughput and, depending on the destination, it may be possible to select a more efficient route through the choice of outbound network.
Multihoming is the practice of connecting a host or a computer network to more than one network. This can be done in order to increase reliability or performance. A typical host or end-user network is connected to just one network. Connecting to multiple networks can increase reliability because if one connection fails, packets can still be routed through the remaining connection(s). Connecting to multiple networks can also improve performance because data can be transmitted and received through the multiple connections simultaneously, multiplying throughput and, depending on the destination, it may be possible to select a more efficient route through the choice of outbound network.
Implementation
IPv4
Classic multihoming is the dominant technique for IPv4. This requires that a network have its own public IP address range and a public AS number. While multihoming with multiple addresses has been implemented for IPv4, it is not generally used, as host implementations do not deal well with multiple addresses per interface which requires the use of "virtual interfaces". It is also possible to implement multihoming for IPv4 using multiple NAT gateways.
IPv6
Classic multihoming can be done in the same way for IPv6 as in IPv4, using Provider Independent Address Space (PI), which can be used to balance traffic across multiple providers. Some regional Internet registries (RIR) such as RIPE have started to allocate /48s from a specific prefix for this purpose. RIPE allocates IPv6 provider-independent address spaces /48 or shorter from 2001:678::/29. Multihoming with multiple addresses has been implemented for IPv6. For outgoing traffic, this requires support on the host, either protocol agnostic (Multipath TCP, SCTP, QUIC, etc.) or specific to IPv6 (e.g. SHIM6).
Other solutions
Automated renumbering. If one uplink goes down, all addresses in the network will be renumbered into a new /48 subnet. DNS and firewall records must be updated to redirect traffic to a different /48 subnet. This renumbering will break live TCP and UDP sessions. Locator/Identifier Separation Protocol (LISP)
See also
Dual-homed Host Identity Protocol (HIP) Identifier/Locator Network Protocol (ILNP) Load balancing Locator/Identifier Separation Protocol (LISP) Media-independent handover or vertical handover in IEEE 802.21 Mobile IP Site Multihoming by IPv6 Intermediation (SHIM6)
References
Text derived from https://en.wikipedia.org/w/index.php?oldid=1354845870 under CC BY-SA 4.0; modifications have been made.