[Re: http://tools.ietf.org/search/draft-hain-ipv6-ulac-01]

Mark Smith nanog at 85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org
Wed Apr 21 04:57:24 CDT 2010

On Wed, 21 Apr 2010 01:46:47 -0400
Daniel Senie <dts at senie.com> wrote:

> I see a need for stable, permanent blocks of addresses within an organization. For example, a branch office connecting to a central office over VPN: firewall rules need to be predictable. If the branch office' IPv6 block changes, much access will break. This is directly analogous to how RFC1918 space is used today in such environments.
> There is a need to have organizations be able to either self-assign or RIR-assign space that they own and can use without trouble within their network. That address space need not be routable on the public networks.
> In general I think this draft has merit.

Unique Local Adresses, of which the linked draft is specifying a subset,
were specified in RFC4193, published in October 2005. They meet all the
requirements you've stated. You might also want to have a look at
RFC3879, "Deprecating Site Local Addresses" for the reasons why IPv6
Site Local addresses, the direct IPv6 equivalent of RFC1918 addresses,
were deprecated. Many of the reasons provided also apply to using IPv4
RFC1918 addresses.

This draft is about a centralised registry for one half of the ULA
space. It is debatable whether it is necessary, as ULAs shouldn't leak
out of a site using them. The major concern is that if they are
globally registered, then some people will start believing that
they can use them as global addresses, and start demanding other
parties such as their ISP or IXes route them, instead of getting
proper global addresses for that purpose. As an example of the risks, an
informal registry for non-central ULAs has been created at sixxs.net.
As a single ULA /48 should be enough for most organisations, looking at
the list, it seems that some people are already attempting an addressing
'land grab'. I can't even reach the website of one of the people who as
registered 7 /48s. It's a bit hard to believe he has a large enough
network to need 458 752 subnets ...


I think the fact that people have listed them there also means that
they now think they now globally 'own' those addresses, and should
there be a (very unlikely) collision, would argue that the address
space was theirs first and point to that list. While duplicated ULAs
shouldn't happen, it shouldn't matter if it does, unless those two
organisations want to interconnect directly. 

ULAs are meant to be stable addressing for inside of your network.
They are not meant to be leaked outside your network under most
circumstances. The only time routes for your ULA address space
may appear outside of your network is if you have a direct link to
another organisation (i.e. a backdoor link), and you want to avoid
using your Internet transit to reach them and vice-versa. In BGP terms,
when you announce some of your ULA address space to the other
organisation, you'd attach a NO_EXPORT community.


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