June 2018
Intermediate to advanced
368 pages
11h 1m
English
Content preview from Managing Mission - Critical Domains and DNS
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TTL considerations
When you have a hostname with both A and AAAA records, the TTLs for those records can introduce additional factors in processing, such as when we are dealing with nameserver hostnames that may exist as glue records in the parent zone (See Chapter 10, Debugging Without Tears – DNS Diagnostic Tools).
Consider the following:
ns1.example.com. 500 IN A 192.168.1.13ns1.example.com. 300 IN AAAA 2001:1838:f001::13
A resolver making a fresh NS query for example.com to one of the .COM root servers would receive the A and AAAA records back in the ADDITIONAL SECTION ("courtesy" additional data).
What the resolver should do with the A record after the AAAA record expires is unspecified.
In some situations, it can lead to a window where ...
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