Subject: new issue: [LL24] Don't configure needless LL addresses

From: Erik Guttman <[email-masked]>
Date: Tue, 11 Feb 2003 15:17:50 +0100 (CET)

Description of Issue  Don't configure needless LL addresses    
Submitter Name  Robert Elz    
Submitter Email Address  [email-masked]
Date first submitted  9 Feb 2003    
Reference
http://www.merit.edu/mail.archives/zeroconf/2003-01/msg00262.html
http://www.merit.edu/mail.archives/zeroconf/2003-01/msg00548.html
http://www.merit.edu/mail.archives/zeroconf/2003-02/msg00000.html
Comment Type ['T'echnical | 'E'ditorial] T 
Priority ['S' Must fix | '1' Should fix | '2' May fix ] S 
Section 1.5

Rationale/Explanation
of issue: See LL1 Lengthy description of problem: See LL1 Requested

Change: 

Delete all of section 1.5, and replace it with:

Having addresses of multiple different scopes assigned to an interface
with no adequate way to determine in what circumstances each address
should be used leads to complexity for applications and confusion for
users. A node with any address assigned for a link can communicate with
all other devices on that link, whether those other devices use
link-local addresses, or routable addresses. 

For this reason, a host that obtains, or is configured with, a routable
address on an interface, SHOULD NOT attempt to configure a
link-local address on the same interface.

Where a link-local address has been configured on an interface, and a
routable address is later configured on the same interface, the host
MUST always use the routable address when initiating new communications,
and MUST cease advertising the availability of the link-local address
through whatever mechanisms that address had been made known to others.

A host SHOULD continue to use the link-local address for communications
underway when the routable address was configured, and MAY continue to
accept new communications addressed to the link-local address.

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From: Erik Guttman <[email-masked]>
Date: Tue, 11 Feb 2003 15:26:16 +0100 (CET)

Please also see http://www.spybeam.org/ll23.html

> accept new communications addressed to the link-local address.

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 E r i k   G u t t m a n                        
 N1 Installation and Provisioning               cell: +49 172 865 5497 
 Sun Microsystems                     pager: [email-masked]

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From: Keith Moore <[email-masked]>
Date: Tue, 11 Feb 2003 09:47:16 -0500

I support the intent, but with changes / caveats

1. this is not sufficient by itself.  there must be a uniform way for networks
   to give hosts routable addresses, and LL hosts MUST (or at least SHOULD)
   implement that.

2.

> > link-local address on the same interface.

... unless explicitly (manually?) configured to do so.

> > MUST always use the routable address

...as a source address...

> > when initiating new communications,

...unless the application unambiguously specifies that another address be
used.

> > through whatever mechanisms that address had been made known to others.

this is not, in general, a host function - imposing MUST on something the host
does not control does not seem like a good idea.  suggest:

It is also desirable for hosts and applications to cease advertising
availability of services at link-local addresses once those services are
available through routable addresses, and it is necessary to cease advertising
availability thorugh link-local addresses once those services are no longer
available through link-local addresses.

---

From: Robert Elz <[email-masked]>
Date: Thu, 13 Feb 2003 16:05:47 +0700

Date:        Tue, 11 Feb 2003 09:47:16 -0500
    From:        Keith Moore <[email-masked]>
    Message-ID:  <[email-masked]>

  | 1. this is not sufficient by itself.  there must be a uniform way for
  |    networks to give hosts routable addresses,

See my previous message, (just a few minutes ago), I don't think that
is required.

  | ... unless explicitly (manually?) configured to do so.

Fine.

  | ...as a source address...

Fine.

  | ...unless the application unambiguously specifies that another address be
  | used.

Fine.

  | > > and MUST cease advertising the availability of the link-local address
  | > > through whatever mechanisms that address had been made known to others.
  | 
  | this is not, in general, a host function - imposing MUST on something
  | the host does not control does not seem like a good idea.

No, with LL addresses, it must be a host function - the host invents its
own address, the only way that the host can ever be found, is when the
host makes that address known to others (somehow).   That's what I call
"advertising" it.   Any number of methods might exist by which this is
done, but they all necessarily originate at the host.  Once a routable
address is available (under this proposal) the host must no longer tell
anyone else about its LL address via whatever this advertising mechanism
happens to be (which says nothing at all about what may have happened
prior to this, nor does it require the host to use the same mechanisms
for its routable address, which may be inappropriate).

So, I don't think we need your suggested change there.

kre