North American Network Operators Group
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Re: ULA BoF

  • From: Iljitsch van Beijnum
  • Date: Fri Jun 01 19:07:43 2007

On 2-jun-2007, at 0:43, Joel Jaeggli wrote:

One of the potential values of unique private address space is the
ability to built your own internets. Now whether there is value to
unique but private address space that is significantly higher than
private but non-unique address space (1918 style) or simply obtaining
your own address space the normal way is a good question. presumably an
administrative hurdle has to be crossed in the former and later cases
but not the middle one.

I think not everyone has a full understanding of why the IETF came up with unique local addressing for IPv6. The idea was NOT to create a new class of address space in addition to RFC 1918-style private addresses and regular globally routable address space. The main issue was that the existing equivalent of RFC 1918 in IPv6, site local addresses, required extensive special case handling in routers and applications, without a clear definition of how this was supposed to work in practice. See http://www.ietf.org/rfc/rfc3879.txt for the details.

Other address types also require special case handling in IPv6 such as link local addresses. Every IPv6 system (host or router) is required to have an address in the prefix fe80::/64 on all of its interfaces. This means that the fe80::/64 prefix is present on more than one interface, which defies all previously known rules about routing. But since packets using those addresses aren't allowed to pass through a router, that's not really a problem.

The idea behind site local is the same, except that you can have a few router hops within a site. There is no convenient location where you can kill all site local packets so they don't leave the "site" like you can with link locals.

Additionally, there's the issue of organizations that each use local addressing and end up merging their networks. Non-unique addressing makes this very hard.

Solution: new type of local addresses that doesn't require any router magic to keep the packets within the site, and is globally unique so network merging isn't an issue.

This means that despite some different properties, ULA space is really the IPv6 equivalent of RFC 1918 space and NOT some kind or bastard invention that is secretly trying to be global space.