> How many addresses has your site's DNS cache looked up in the past week?
> How many different ISPs are involved? One thousand? Ten thousand?
>
> Client-side indirection means that you have to check every one of those
> ISPs for changes. Server-side indirection means that you have to check
> one ISP, namely yours, for changes. The frequency of checks per ISP is
> somewhat higher for server-side than for client-side, but client-side
> involves vastly more ISPs.
Whoa! I think I detected a bogon.
If you're setting TTLs in order to catch a site S renumbering within
a time Tr, then compare the two cases
Case 1: DNS master for S checks all the upstream prefixes and
generates a set of complete address records for hosts in site S (be
they AAAA or A6 with prefix len = 0).
Case 2: The zone file for S indirects the prefixes at some level to
data held by its upstream provider(s) using the A6 prefix name field.
In case 1, the zone must bound the TTL of every address record by Tr.
In case 2, the provider(s) must bound the TTL of their portion of the
address by Tr. (Or, S's zone must provide an indirection with TTL
bounded by Tr.) The A6 records owned directly by the host may have
TTLs much longer that Tr, depending on what the site knows about its
own habits and practices.
So in case 1 clients of site S must re-fetch every address record
they need at a frequency approximately 1/Tr.
In case 2, they only need to fetch the common prefix record at the
rate 1/Tr.
> Bottom line: This is not a benefit for A6.
Bottom line: there is such little experience with A6 that people's
thinking is sometimes a bit muddy.
Matt Crawford
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