TTL settings on LBR''s main zone

Re: TTL settings on LBR''s main zone

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At 9:47 PM -0700 10/7/01, eric@micromaniac.com wrote:
>I have 2 servers load balanced 50/50, with LBR TTL 120, interval 30, hostlife
>60. About 30 other domains point to the LBR, and they work fine. I currently
>have the TTL's of those other domains set at the default settings. But I have
>the TTL's of the main domain set to refresh 2000 and caching, retry and TTL of
>SOA to 600. (I didn't change the other domains since they are CNAMEd to the
>main domain anyway.)
>
>But is changing the main domain's TTL's even necessary since the LBR is set at
>120/30/60? It probably can't hurt, but I've heard stories of some major ISPs
>ignoring ("changing") low TTL's to 24 hours.

First, let's talk about the settings of the zone that contains the
load balance record. The refresh, retry, and expire settings only
affect slave service. You can find definitions of them in our
glossary of terms, which is in the online help and on our website.

The negative caching value at the top of the zone is used as the TTL
for a negative result. In other words, if someone queries your server
for "bogus.example.com" and your server is authoritative for the zone
"example.com", your server will respond with an indication that there
is no such domain name. This response comes with a TTL, indicating
that the source of the query (likely to be another server) is
permitted to remember, or cache, the fact that there is no such
domain name for that number of seconds.

The "TTL of SOA" field at the top of the zone only affects the zone's
SOA record itself; it doesn't affect any other record.

None of this directly affects the load balance record, since the load
balance record has its own explicit TTL. The only way these SOA
values might affect a load balance record is if the slave server(s)
involved isn't/aren't QuickDNS for Mac OS servers that you control;
in such a case, a newly-created load balance record won't reliably
work until all such slave servers have performed a successful refresh
check.

It is true that some major ISP's ignore TTL's, or increase them to
some minimum value internally. This is unfortunate, and violates the
rules (and stated intent) set forth the RFC's, but there isn't much
you can do about it. The biggest offender is, of course, AOL.
____________________________________________________________________
Chris Buxton Men & Mice
cbuxton@menandmice.com Making DNS Easy

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