June 2018
Intermediate to advanced
368 pages
11h 1m
English
Content preview from Managing Mission - Critical Domains and DNS
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Can't You Just Set Your $TTL To 0?
One may wonder whether you could have your DNS changes visible across the internet instantly by setting your TTLs to 0.
You could do that. By doing that you are telling all client resolvers and recursors to not cache your zone (or specific RRs within the zone) and come back and ask one of your authoritative nameservers every single time they get a query for it.
It's expensive to do that–not only in the engineering-speak meaning of "expensive"–in that every query has to go through the entire lookup process every time (see Chapter 6, DNS Queries in Action)
But since many commercial DNS providers charge by the query (usually in terms of cost-per-million), it can be literally, expensive.
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