Classic multihoming is costly, since it requires the use of address space that is accepted by all providers, a public Autonomous System (AS) number, and a dynamic routing protocol.
[9] This technique has the advantage of working like IPv4, supporting traffic balancing across multiple providers, and maintaining existing TCP and UDP sessions through cut-overs.
Critics say that the increased size of routing tables needed to handle multi-homing in this way will overwhelm current router hardware.
Proponents say that new hardware will be able to handle the increase due to cheaper memory, which drops in price according to Moore's law.
Because many ISPs filter out route announcements with small prefixes, this will generally require a large "ISP-sized" IP allocation, such as a /32, to ensure global reachability.
However, from a pragmatic perspective, allocating a /32 is equivalent in global address space cost to allocating a single IPv4 address, and this may be acceptable if, as seems to be likely for the foreseeable future, the number of multihomed sites can be numbered only in the millions, as opposed to the many billions of non-multihomed endpoints which are anticipated to comprise the vast majority of IPv6 endpoints.
[citation needed] Some regional Internet registries (RIR) such as RIPE have started to allocate /48 from a specific prefix for this purpose.