newbie to DDNS question RE: foo.com.log and foo.com.ixr

[Anthony Golia]

Hi.

I'm familiar with most other aspects of Bind except the DDNS
implementation.  I notice that foo.com.log and foo.com.ixfr get created
when dynamic DNS is enabled (and used).  Also, Bind seems to
periodically overwrite my foo.com zone file, incorporating the
DDNS changes.  Can someone explain (or point me in the right direction):

-    How/when are these foo.com.ixfr and foo.com.log files used?
-    Given that I nightly, automatically generate my foo.com zone file,
how can I prevent losing the dynamic info?

Any help is appreciated.

--
Anthony