Subject: Re: IETF 51 ZEROCONF Minutes

From: Stuart Cheshire <[email-masked]>
Date: Tue, 11 Sep 2001 19:54:45 -0700

>IP addresses are intended to be used directly.   DNS is optional.

Is this really a serious argument?

Are IPv6 addresses intended to be used without a naming protocol?

If you really want, IPv4 link-local addresses can be used directly. We 
can plug our two laptops together with a crossover Ethernet cable, you 
can read your IP address from your screen, and I can type it into my 
AppleShare client. It works fine, but a naming protocol is obviously 
better, and a service discovery protocol is better than that.

Why are IPv4 link-local addresses different to IPv6 link-local addresses
in this respect? You can use either without a naming protocol, but would 
you *want* to?

RFC 2460 does not discuss naming and DNS for IPv6 addresses. What is 
different about this draft?

>Many applications expect IP addresses to be stable for weeks or more 
>and not to be changed on a whim.

If you unplug your laptop from the office network and take it home with 
you, then applications that expect IP addresses to be "stable for weeks 
or more" are not going to work, no matter how you assign the address.

If you don't want to unplug the computer from the network and take it 
home with you, link-local addresses are stable.

>DHCP can be used to assign long-term addresses -
>just keep renewing the same lease.

Your link-local addresses is long-term -- just keep defending it.

You seem to have some misconception that link-local addresses keep 
changing at random for no reason. They do not. Link-local addresses only 
change if two hosts are found to be using the same address. If two hosts 
are found to be using the same address then networking doesn't work 
reliably no matter how the address was assigned, so selecting a new 
address is the best course of action in that case.

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

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From: Keith Moore <[email-masked]>
Date: Wed, 12 Sep 2001 13:45:17 -0400

> Is this really a serious argument?

yes it is.  first because DNS is not fast or reliable enough
for some kinds of applications; second, because DNS names are 
quite often overloaded and are not precise enough to be used
as "endpoint identifiers" in distributed systems; third, because
systems don't always have a reliable means of determining their
DNS names (or their view of their DNS name may be different than
the public view of their DNS name); and fourth, because we 
need to retain the option of implementing other name-to-address
lookup services without making them dependent on DNS.

I can elaborate on all of these if necessary.

> Are IPv6 addresses intended to be used without a naming protocol?

we're talking about IPv4 here, not IPv6.  and we're talking about
DNS specifically here, not just "a naming protocol".

> changing at random for no reason. They do not.

it's a scaling issue.  in a sufficiently large network temporary
partitionings of the network (say via bridges that fail or restart)
becomes a significant impact on reliability.  I'm also concerned
about the behavior of link-local addresses on large bridged networks 
during bootstrapping - say after a power failure.  

stating an expected scale for a network using link-local addresses 
(as I believe you'd agreed is reasonable) would help a lot.  I will
need to re-assess many of my comments in light of this change, and 
I haven't had time to do that yet. 

Keith