Valid TTL's are of the range 0-2147483647. Classless IN-ADDR.ARPA delegation . If the first form is used then step is set to 1. All of start, stop and step must be positive. It is processed similarly to the lhs.
All resource records have the same basic syntax.
Specify the domain name for this record. This specifies how long this record will be cached by caching servers. The valid range is 0-2147483647. This is usually redundent as the class of a zone is specfied in the configuration file prior to reading the zone file. This describes the contents of the rdata section.