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22.What is wrong with the following zone records? 
domain.org.       IN    MX 7    mail.domain.org
mail.domain.org   IN    CNAME   server.domain.org
server.domain.org IN    A       192.168.1.1

Hostnames on the left half of the record must not be fully qualified.
MX record priorities must be in multiples of 10.
CNAME should be CANON for BIND and above.
BIND requires matching IN6 records.
MX records should not point to a CNAME.

Explanation: In the zone file, we can see that mail.domain.org is a CNAME (alias) for server.domain.org and that the MX record points to mail.domain.org. Section 10.3 of RFC 2181 (Standards Track) specifies that the domain name used as the value of a NS resource record, or part of the value of a MX resource record must not be an alias (CNAME).

Reference: http://www.cis.ohio-state.edu/cgi-bin/rfc/rfc2181.html#sec-10

Incorrect Answers
A: The hostnames can be fully qualified.
B: MX record priorities are usually multiples of 10 but this is not a requirement.
C: CNAME should not be CANON for any version of BIND.
D: BIND does not require matching IN6 records.
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