Bind9 named.conf zone file serial number?

Question

Okay. I have heard tell that when one directly modifies the named.conf (or named.conf.local) file, and then restarts Bind9 you need to increment the serial number of the zone file by one.

Why?

Does it need to be different so that other name servers know that it is new record? Also, if I modify more than one zone file, before restarting bind, do I need to increment ALL the serial numbers from all the named zones, or just the ones that were modified?

Answer 1

If you run multiple servers this is how the slaves know a master record has been changed. This saves a massive amount of chat on the network. Every file you modify has to have its' serial increased. Also these serials should really contain a date element and last 2 digits serialised to allow up to 10 zone changes per day. This is to  allow for sites which grow rapidly and have regular changes of machines, especially when updated from dhcp.

Answer 2

If your DNS is only used in your network (ie. it need not be accessible by people from outside your network), you need not be concerned about those numbers.