Concise Guide to DNS and BIND, The

Masters, Slaves, and Serial Numbers

The serial number of the SOA record is very important to the correct operation of slave servers. Each time you edit your zone, the serial number must be increased so that the slave server can detect that the zone has been updated. Whenever the slave server notices that the serial number has changed, it performs a zone transfer and updates its cached zone file. In Chapter 3, you can find a discussion of how the SOA controls zone transfers and tips about how to plan changing zone data so server moves and similar changes can be done in a planned and orderly manner.

If some users are getting old data from DNS, the cause could be that one of your slave servers is still serving the old zone data because it has not ...