Re: [nznog] BCP / Guidance on IPv6 prefix size to provide to customers

On 02/01/2015 20:56, Jeremy Visser wrote:

On 2 Jan 2015, at 08:22, Ben wrote:

...

The general recommendation seems to be to give out /48s to users. Although you may only have a /32 at the moment, you can apply for more space in the future if you require it.

It is generally given that /48 is the smallest allocation that one can advertise over the internet. And if a customer wants to multihome in multiple locations then each location should have a /48 at the least.

The latter isn’t a valid reason for the former, as space assigned to customers by ISPs is by definition non-portable.

There was an argument, which I think was in (obsolete) RFC 3177, that if all providers hand out the same length prefix, customers would never have to redesign their site addressing plan if they switched providers and had to accept a longer prefix. The more recent recommendation is that site numbering plans should simply number subnets compactly rather than sparsely, to avoid needing a short prefix when it isn't strictly necessary. All the same, handing out /56s means assuming that your customers never need 257 subnets. That may sound like a lot, but think about possibilities such as large numbers of virtual subnets. Brian

Not arguing against /48’s or anything, though.

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