Subject: RE: draft-ietf-zeroconf-ipv4-linklocal-03.txt

From: Stuart Cheshire <[email-masked]>
Date: Wed, 11 Jul 2001 00:31:57 -0700

>In my opinion, is no reason to change the wording to "should".  I think the
>concept that the169/254/16 prefix packets are coming from a "friendly"
>link-local network, the use of some other address may look like an
>"intruder".  I like the original wording best.  Maybe Thomas could give a
>reason for the "too strong"?   

I think the reasoning is this:

Say you have two devices on the same physical Ethernet. Device A 
implements link-local addresses, and has assigned itself one. Device B 
does not implement link-local addresses, but has a manually configured 
address of 10.0.0.1.

These devices are on the same physical Ethernet. Is it useful for the 
link-local draft to prohibit them from talking to each other?

We may like to dictate that Device B MUST implement link-local addresses, 
but the world doesn't work like that. If the vendor of Device B doesn't 
have the engineering resources to implement link-local addresses, then is 
it better for the user if the devices can talk safely, or not?

Stuart Cheshire <[email-masked]>
 * Wizard Without Portfolio, Apple Computer
 * Chairman, IETF ZEROCONF
 * www.stuartcheshire.org

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From: Daniel Senie <[email-masked]>
Date: Wed, 11 Jul 2001 09:34:08 -0400

>link-local draft to prohibit them from talking to each other?

If a link-local device has only 169.254/16 in its admittedly small routing 
table, won't it just look at the 10/8 address and decide there's no route 
to that network? There's no default route, and no way for it to know that 
it should try to ARP for that 10/8 address. So, it still won't communicate.

>it better for the user if the devices can talk safely, or not?

My point here is that if the other device tries to answer with the 
non-link-local address, a box working in link-local-only mode may have no 
way to respond. If boxes are going to use multiple addresses, then we have 
to handle communicating with boxes which don't know how to reach any 
addresses other than link-local.

Alternatively (and I'm not in favor of this alternative), we could say that 
a box which is running link-local-only should indeed treat 0/0 as link 
local, and ARP for any and all addresses. This would seem to be a very bad 
idea. While it would allow a device in link-local-only mode to talk to a 
box with both link-local and another address to function, it would also 
allow a link-local-only box to talk to a box with only a configured 
address. This box with the configured address would not know to ARP for the 
link-local address on the local wire, though, if it's only configured for 
non-link-local. I think any change in this area would require touching most 
hosts code to ensure compatability.

-----------------------------------------------------------------
Daniel Senie                                        [email-masked]
Amaranth Networks Inc.                    http://www.amaranth.com