Subject: RE: utility of dynamic DNS

From: "Peter Ford" <[email-masked]>
Date: Fri, 1 Mar 2002 10:18:55 -0800

I would offer that we select the "thing" that looks the most persistent
to be the persistent identity.  If the choices are: DNS name vs IP
address, I think most people would recognize that the DNS name is the
persistent identity.   And it is probably the one most people would want
to use, especially in light of the problem of writing down IP addresses.
This is just when we are talking about Hosts.   What if we were to
include services?  

In terms of scalability debates, I have yet to see an analysis to
support claims of more or less scalable wrt DDNS, Mobile IP, etc.   We
should probably try to move the debate from "proof by emphatic
assertion" to analysis.

Most of the statements I have seen on the scalability topic remind of
the debates in prior decades used by a couple of telcos to dismiss the
viability of mobile cellular telephony.  In the end, the HLR/VLR
paradigm has been one of the most successful deployments in the history
of technology (the wheel has it beat, not clear the Internet has - yet).
(and I can't help mentioning that HLR/VLR is an example of an
architecture analogous to DDNS where a mobile phone number is a name).
Perhaps there are theses already tackling these issues?

At a minimum, DDNS covers today's common cases of managing the DNS.
It's utility is quite good for the common roaming/mobile cases, today.
More importantly, it is used to solve the basic network Name to IP
binding problem for common deployments such as enterprise.  Everyday
people move across IP subnets due to office moves and DDNS just works
without network administration intervention. 

In reality, the debate should not end up being either/or in nature.   It
is likely that a multi-tier set of mechanims will operate.  We already
see that with services where we have very long lived names in the DNS,
shorter lived names in the IP space, and short term mapping of those IP
addresses to actual machines being managed by load balancers and their
ilk.

Regards, peter

-----Original Message-----
From: Geoff Huston [mailto:[email-masked]] 
Sent: Friday, March 01, 2002 2:04 AM
To: Francis Dupont
Cc: Theodore Tso; Keith Moore; Pete Resnick; Randy Bush; Jakob Schlyter;
[email-masked]
Subject: Re: utility of dynamic DNS 

The essence of the architecture of mobility is to allow the identity of
the 
mobile device to remain constant while allowing the identity of the 
location of the device within the network to vary.  The dynamic DNS 
approach attempts to bind the domain name as the device's persistent 
identity and allows the current IP address to equate to the device's 
current location.

Obviously, as already pointed out, the restriction here is that the
device 
cannot support persistent state across location changes, but worse, as
far 
as I can tell, is that it is an approach that has poor scaling
properties. 
In order to operate correctly in a timely fashion the relevant parts of
the 
DNS now require very short TTLs. At that point many of the assumptions
of 
the scaleability of the DNS tend to be called into question. Is the gain

worth the potential scaling pain?

If the issue here is one of circumventing some level of circuitous
traffic 
paths, then it seems to me that there is really not much to gain - any 
cursory examination of Internet paths in terms of cable route miles
reveals 
a healthy level of gratuitous overhead in any case - the so called
direct 
paths you get from dynamic DNS updates as a solution to mobility may
well 
be no better than the dog-leg route you were attempting to avoid.

---

From: Keith Moore <[email-masked]>
Date: Fri, 01 Mar 2002 23:25:07 -0500

> 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