What does "rdns = false" mean in the [libdefaults] section of krb5.conf?

Issue

What does rdns = false mean in the [libdefaults] section of krb5.conf?
What does dns_lookup_realm = false mean in the [libdefaults] section of krb5.conf?
What does dns_lookup_kdc = false mean in the [libdefaults] section of krb5.conf?

[libdefaults]
 default_realm = EXAMPLE.COM
 dns_lookup_realm = false
 dns_lookup_kdc = false
 rdns = false
 ticket_lifetime = 24h
 forwardable = yes

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