RFC 1537 (rfc1537) - Page 2 of 9
Common DNS Data File Configuration Errors
Alternative Format: Original Text Document
RFC 1537 Common DNS Data File Configuration Errors October 1993 - Refresh: The SOA record of the primary server is checked every "refresh" time by the secondary servers; if it has changed, a zone transfer is done. - Retry: If a secondary server cannot reach the primary server, it tries it again every "retry" time. - Expire: If for "expire" time the primary server cannot be reached, all information about the zone is invalidated on the secondary servers (i.e., they are no longer authoritative for that zone). - Minimum TTL: The default TTL value for all records in the zone file; a different TTL value may be given explicitly in a record when necessary. (This timer is named "Minimum", and that's what it's function should be according to STD 13, RFC 1035, but most (all?) implementations take it as the default value exported with records without an explicit TTL value). For top level domain servers I would recommend the following values: 86400 ; Refresh 24 hours 7200 ; Retry 2 hours 2592000 ; Expire 30 days 345600 ; Minimum TTL 4 days For other servers I would suggest: 28800 ; Refresh 8 hours 7200 ; Retry 2 hours 604800 ; Expire 7 days 86400 ; Minimum TTL 1 day but here the frequency of changes, the required speed of propagation, the reachability of the primary server etc. play a role in optimizing the timer values. 2. Glue records Quite often, people put unnecessary glue (A) records in their zone files. Even worse is that I've even seen *wrong* glue records for an external host in a primary zone file! Glue records need only be in a zone file if the server host is within the zone and there is no A record for that host elsewhere in the zone file. Beertema
