Multihoming with PA, was: Re: New ARIN ipv6 allocation policies

Iljitsch van Beijnum iljitsch at
Tue Sep 5 11:23:26 CEST 2006

On 5-sep-2006, at 10:54, Jeroen Massar wrote:

> The idea here is that PA is PA, and PI is PI. That means that the  
> PA blocks _should_ only be announced as the full PA block and no  
> more specifics.

Have a look at: 

I'll be submitting this draft shortly; comments are welcome.


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 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.

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