Subject: RE: 169.254/16 IP addresses

From: "Hattig, Myron" <[email-masked]>
Date: Mon, 17 Apr 2000 17:37:18 -0700

I second the below questions ... what exactly are the differences between
link-local and private addresses?

More embedded questions below as well ...

From: Thomas Narten [mailto:[email-masked]]
> What do NATs do in general with multicast? One BIG problem I can see
> is larger sites with multiple NAT/egress boxes. If the multicast
> packet reaches more then one egress NAT, multicast packets get
> replicated (incorrectly, since the packets are duplicates) out of
> different points with different source addresses. Not good for the
> Internet.

From Bernard Aboba:
> > One of the reasons we created a linklocal prefix was so that
> > we could get behavior different from private addressing for
> > situations where this made sense. If we blur the distinction
> > then we'll lose the ability to have truly linklocal behavior
> > when we need it. 

Please clarify exactly what gets blurred and exactly what is lost.
From the context of a host traversing a NAT box, I see link-local
addresses as logically equal to private addresses (RFC 1918).

-myron

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From: Thomas Narten <[email-masked]>
Date: Tue, 18 Apr 2000 08:06:00 -0400

> addresses as logically equal to private addresses (RFC 1918).

One difference is that by declaring 169.254/16 to be link-local, we
are giving nodes license to simply declare all destinations covered by
169.254/16 as being on-link and directly reachable. I.e., folks will
wire that knowledge into implementations.  If someone then comes along
later and says that some of the subnets of 169.254 are actually on
other links and only reachable via a router, that router will probably
have to do something like proxy ARP to properly handle all devices
that assumed link-local really meant link-local.

It might well make sense to just use one of the already-reserved
private address ranges (e.g. net 10) for doing multi-link
autoconfiguration. Is it reasonable to asume that this technique
(numbering multiple links automatically) will take place ONLY on
isolated networks? I.e., there will be no conflict with net 10? I.e,
are we willing to state definitively that a node will not have both
global addresses and these autoconfigured site-local (to borrow a name
from IPv6) addresses simultaneiously?  I.e., the direction being taken
with link-local addresses is that a node can have both link-local and
global address simultaneously. I'm not sure we want to do the same for
site-local addresses.

Thomas