Re: IPv6 w.g. Last Call on "Unique Local IPv6 Unicast Addresses"

[Iljitsch van Beijnum <iljitsch@muada.com>]

On 24 okt 2003, at 18:14, Hans Kruse wrote:

> 2.  Several folks stumbled over the wording (in section 1.0) that 
> "applications may treat these address[sic] like global scoped 
> addresses". How about:
> "Applications may treat these addresses like global scoped addresses; 
> such applications will function correctly within the reach of the 
> local addresses.  Sites using a mixture of Globally Routable and Local 
> addresses may experience sub-optimal application behaviour, see 
> sections 8.0-10.0 for further discussion".
I think this will only confuse people who aren't aware of all the 
details. But the problem is more fundamental than wording issues 
anyway. The problem is that there are two types of uses for local 
addresses:

1. To number systems/interfaces that are only accessible from withing 
the local network.

2. To have stable addresses for systems/interfaces regardless of 
intermittant external connectivity and renumbering.

In the case of 1. the scope is site local, although the difinition of 
"site" may be subject to change. Being able to route these addresses 
throughout the internet would be more of a drawback than a usable 
feature, as packets using these addresses may not enter or leave the 
network. In the case of 2. having the addresses be globally routable 
throughout the internet would be extremely desirable: having addresses 
that are stable within the site is good, having addresses that are 
stable throughout the net is even better.

If we recognize that unique local addresses will be used in both 
capacities and there is a significant chance that a locator/identifier 
separation mechanism could make these addresses globally usable (if not 
immediately routable), then it's obvious there are going to be 
problems. For instance, coming up with relatively simple filters that 
accommodate both uses of the addresses at the same time would be a big 
challenge. Having to change the default filtering policies that come 
with the OS for huge numbers of boxes would be another issue.

I think that either it must be explicitly stated which type of 
addresses we're talking about here. It would probably be best to only 
specify type 1 and see what can be done for type 2 with 
locator/identifier separation mechanisms.

> 4.  Regarding DNS; there were some comments regarding RFC1918-style 
> lookups.  I assume the concern was regarding reverse lookups (the 1918 
> root server load issue).  However, the Local addresses in this draft 
> are unique (FC00::/8) or nearly unique (FD00::/8).  As such there is 
> really no reason not to allow reverse lookups for FC00::/8 in the 
> global DNS.
It would make sense to delegate authority for the "nearly unique" type 
to a set of anycast addresses so that people can provide reverse 
mapping information for their own local address ranges through DNS 
servers listening to those anycast addresses.


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