Re: To address or NAT to address?

[Christian Huitema <huitema at research.telcordia.com>]

At 10:09 AM 12/2/99 -0800, Charles E. Perkins wrote:
>
>> With this in mind I hope that the same folks who complained about
>> increased dependencies on DNS by NATs, would be equally vocal in
>> complaining about increased reliance on the DNS by IPv6 (which claimed
>> to be an improvement over NATs).
>
>DNS is supposed to be a way to resolve domain names into IP addresses.
>How else would one get an IP(v6) address from a domain name other
>than by using DNS?  Am I missing something here?

The IPv6 A6 record, which I helped design, map a host name to a tuple of
(prefix length, prefix name, binary suffix). The prefix name is a DNS name.
In order to actually get the address, one should go read the A6 record(s)
of the prefix, then combine prefix(es) and suffix to obtain address(es).
The idea is to facilitate renumbering by storing the prefix(es) in exactly
one place.

One could say that this structure implies an "increased reliance on the
DNS", in the sense that one will need to access two records instead of one
in order to obtain the address. In fact, we may need more than two
transactions, if the prefix itself is built from another prefix. On the
other hand, there are at least three ways to diminish this reliance:

1) DNS server can provide a copy of the prefix-name's A6 record in the
"additional information" field of responses, so that the second transaction
can be served from the cache,

2) In "Intranet" environments, a working set of prefixes will be present in
the cache anyhow,

3) In really constrained environment, network managers may choose to
arbitrage between ease of renumbering and reliance on the DNS, and set the
prefix length to zero, thus falling back to IPv4 like operation.

In short, this issue was discussed at length in the IPv6 working group, and
the benefits of easy renumbering/reconfiguration were deemed to exceed the
"extra reliance."
-- Christian Huitema