[dns-operations] should recursors think there are only delegation data in tld name servers?

[刘明星]

hi,
    if a recursor ask a tld server for A records of a domain name, such as
a.test.tld, the .tld server return a nxdomain response to the recursor. In
this case, the recusor does not know whether there are other domain names
related to test.tld, like b.a.test.tld, b.test.cn and c.b.test.cn, so that
next time it should query the tld again when it receives queries for such
domain names. Consequencely, If a ddos flood of random third-level domain
names hits the recusors, the flood also be redirected to the the tld the
domain names belong to.
   I want to know whether there other types of data except delegation data.
If there are only delegation data in tld some servers , the recursors
should send less unnessary queries to tld servers when they receive a large
of queries for a random third-level domain names. As a result, the tld
servers escape from the disasters.

Liu Minxing
cnnic
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