Subject: LL1 and LL23

From: Mika Liljeberg <[email-masked]>
Date: 19 Feb 2003 22:17:24 +0200

I'm leaning towards rejecting the issue:

"Supporting multiple address per interface, where one address is v4 LL
and other addresses are configured leads to a scoped address problem.
Hosts must select which source address to send datagrams with from that
interface. In addition, application considerations are much more complex
when there are multiple scopes in which the application must operate
in."

While there is some justification to this, I believe that the potential
problem has been blown beyond its true proportions. With LL-only nodes,
such problems are indeed inevitable and cannot be fixed by the measures
proposed in either LL1 or LL23. With nodes having both LL and routable
addresses, I'm not convinced.

The text argues that multiple address per interface are a problem. What,
then, of multihomed hosts? Is this somehow more of a problem than having
a single address on each interface of a multihomed host? Applications
need to deal with that as well.

>From an implementation point of view, both LL1 and LL23 generate
additional code and alternative code paths in a stack implementation. Of
the two LL23 is clearly more demanding. LL1 is less so, but in a hybrid
IPv4/IP6 implementation necessitates alternate code paths for IPv4 and
IPv6 source address selection, where the current wording enables a
shared code path. 

In the recent discussion I have seen zero concrete examples where having
both LL and routable addresses in an interface would result in serious
application problems. Given a sufficiently compelling example, I might
reconsider. However, currently I see few advantages and some definite
disadvantages.

In my mind, the current wording in section 1.5 and 2.5 regarding source
address selection is sufficient and appropriate.

	MikaL