Keith,
I did not argue the persistence of ALL DNS names.
What I did argue is that if I was trying to tell someone how to reach a
particular Internet based service I would write down something that had
a DNS name in it, not something that contained an IP address. For me,
that is a measure of persistence.
I will not argue against the fact that IP addresses have the nice
property that when a host A tells another host B its address (as the src
address of an IP packet) that host A is reachable by that address. I
would argue that property is not persistence, it is temporally bounded
reachability (TBR - we can have a bof to get a better name).
Now, let's look at most of the systems that you refer to that do not
have a DNS name. How many of those hosts connect to the Internet using
dialup connectivity and for the better part of the day do not even have
an IP address? And what about those hosts that have DNS names inside
their corporate networks, but their corporations elect not to publish
those persistent names into the DNS for security fears? Is this what
we are supposed to use as evidence that IP addresses are more persistent
than DNS names?
And when those hosts connect to the Internet, what do they use FIRST
when they want to communicate with a peer? (now I have opened the dam
here, haven't I? Strictly speaking they will use the IP address of "."
to get going! Mcast DNS can fix that bug.).
I am not suggesting that all hosts solely use DNS names as a rule. I
will suggest if you want to advertise services and hosts then use DNS
names because that is what works. And I am also arguing that you can
get "good enough" roaming if you use DNS names.
And I am asking whether anyone can actually prove that DDNS is not
scalable (preferably for real Internet applications and uses).
Regards, peter
(P.S. And shouldn't you be asking: "Peter, if you really want hosts to
register their tunnel ends in the DNS, isn't the most likely
implementation one where the host gets a persistent IP address, and gets
many TBR IP addresses over time?" - cheers, peter)
-----Original Message-----
From: Keith Moore [mailto:moore(_at_)cs(_dot_)utk(_dot_)edu]
Sent: Friday, March 01, 2002 8:25 PM
To: Peter Ford
Cc: Geoff Huston; ietf(_at_)ietf(_dot_)org
Subject: Re: utility of dynamic DNS
I would offer that we select the "thing" that looks the most
persistent
to be the persistent identity.
Actually, you want to select the identity that's appropriate for your
purpose. DNS is not inherently better than IP for all purposes.
DNS names are often failure-prone, slow to lookup, and/or out of
sync with reality.
If the choices are: DNS name vs IP address, I think most people would
recognize that the DNS name is the persistent identity.
And if 'most people' treated this as a general rule, they'd be wrong.
There are several situations where IP addresses are more usable
than DNS - the DNS name may not even exist, lookups may not work
outside of a realm, or the name may be bound to an IP address rather
than a host. It is highly dependent on the configuration of the network
where the hosts are located and the DNS servers that serve them.
See draft-moore-nat-tolerance-recommendations-00 for a more detailed
explanation.
We should probably try to move the debate from "proof by emphatic
assertion" to analysis.
Presumably that also applies to assertions about persistence of DNS
names.
Keith