Subject: Dynamic DNS and TTL value 0

From: Mikael Latvala <[email-masked]>
Date: Wed, 01 Dec 1999 17:53:31 +0200

Today almost all the mobile hosts run only client applications which
need to communicate with servers which have been assigned fixed IP
addresses. This trend is about to change, however, when mobile nodes
become more powerful.

Currently there is a large number of ad hoc solutions for allowing host
A to establish a connection with host B which has been assinged a global
but temporary (dynamic) IP address. It goes without saying that these
unique application/protocol based solutions should not be long term.
Rather, there should be a generic mechanism which provides consistent
and accurate bindings between literal host names (e.g. DNS names) and IP
addresses.

DNS might be a solution for this. RFC1034 in sec. 2.3 supports this idea
by saying that "... system [DNS] should be able to deal with subsets
that change more rapidly (on the order of seconds or minutes)". 

Question: Together with dynamic DNS updates and TTL value set to 0 in
all DNS responses does anybody know what kind of performance load this
would place on the network, e.g. any simulation results? I am not so
much concerned with dynamic DNS updates but rather with the increased
number of DNS queries.

Thanks,
Mikael

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From: Jared Mauch <[email-masked]>
Date: Wed, 1 Dec 1999 13:32:11 -0500

I suspect that in an environment such as this, the amount
of extra load that would be an additional 30x, but it would really depend
upon the application that was being done.

	If we were to take the example of VOIP, and the fact that I would
create a host called jared.voip.nether.net, which would be mapped to
always point at a reachable ip at my location, you still have some
minor (and sometimes major, because of some application issues)
internal caching of the dns information.

	If someone procedes to call me voip, it will only look up the A
RR a single time, and keep a (as persistent as udp is) connection to that
until the call is completed, and then do a re-query of the A record
at the time of the next call.

	There will be some expensive (because they are not cached)
dns queries on the recursive server because of the referals, etc, but
the NS records should be able to be cached after the first query, and
you should be in good shape.

	Most nameservers (at least that I have access to) that get queried
frequently would have a lot of spare cpu power to deal with these additional
queries.  The nameserver software would be the only possible performance issue,
but should perform quite well as long as there is no loss to the SOA
nameserver.

	- Jared

-- 
Jared Mauch  | pgp key available via finger from [email-masked]
clue++;      | http://puck.nether.net/~jared/  My statements are only mine.
END OF LINE  |

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From: Paul A Vixie <[email-masked]>
Date: Wed, 01 Dec 1999 10:26:22 -0800

> much concerned with dynamic DNS updates but rather with the increased

ttl 0 for large numbers of active hosts would be fatal to the internet.
(that is, dns caching is all that stands between us and disaster.)

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From: [email-masked]
Date: Thu, 02 Dec 1999 15:37:07 +0900

Mikael,

I have tried to solve the dynamic record issue and I've found
we can 'make it better' using countdown style TTL for those
travelling hosts.

I haven't tried to catch the number of those queries. But I assume
if I make the TTL half, the double number of queries will appear.

yusuke doi

At Wed, 01 Dec 1999 17:53:31 +0200,

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From: Harald Tveit Alvestrand <[email-masked]>
Date: Fri, 03 Dec 1999 00:11:08 +0100

>(that is, dns caching is all that stands between us and disaster.)

Do you have numbers on that?

Not that I don't think it could be true, but it'd be good to see some real 
numbers for once, i.e. if we could document something like:

- Caching efficiency in the DNS is 95%
- DNS traffic is 5% of total Internet traffic
- Therefore, if all TTLs were 0, the traffic on the Internet would double,
   and we'd all be in the World Wide Wait

(NOTE: These numbers are TOTALLY BOGUS!)
But you might have a different disaster in mind.

(Recently I saw a number of TTL 0 records when I looked at load-balancing 
servers, but www.netscape.com is now using 15-minute timeouts; I guess 
their software has been upgraded. Perhaps they saw the danger....or the 
performance drop.... Akamai, for some reason, uses 20 seconds on their 
cacheservers' A records....see a516.g.akamai.net for an example)

                          Harald

--
Harald Tveit Alvestrand, EDB Maxware, Norway
[email-masked]