BGP Community for PA Multihoming

When an organization wants to connect to the internet using two or more Internet Service Providers (multihoming), this is usually done by setting up BGP routing between the organization in question and each of its ISPs. For this, the multihomed organization needs a block of address space. This can either be a provider independent (PI) address block that belongs to the organization, or a block out of the provider aggregatable (PA) address space of one its ISPs. With IPv4, an address block of at least /24 will generally be suitable for multihoming, whether its origin is PI or PA. However, until now, ISPs were encouraged to only accept /32 and shorter prefixes from IPv6 PA space, while end-users generally receive a /48. This makes multihoming with PA address space in IPv6 very difficult. This memo describes a new well-known BGP community attribute for tagging prefixes used for multihoming with PA space in order to facilitate filtering, rather than filter based on prefix length alone.