All MacTCP DNS servers should be set up thusly:

   domain.com.    1.2.3.4    (*)
   .              1.2.3.4    ( )
   .              5.6.7.8    ( )

Where domain.com is the domain you want appended to unqualified DNS names
(eg fred becomes fred.domain.com), and 1.2.3.4 is your primary DNS server,
and 5.6.7.8 is your backup DNS server.  Note the dot at the end of the domain name "domain.com." - although this currently make no difference, a dot at the end of a name forces the name to be absolute, so it is a good idea.

The first column of the default line means "the string to tack on the end
of unqualified names".  Ie, info -> info.curtin.edu.au.

The first column also means "only query this server if the name matches
this domain".

The default also means "if NO server matches the query then use this server"

So if you have

   domain.com.    1.2.3.4    (*)
   .              5.6.7.8    ( )

Then all domain.com queries (including all unqualified names) will query
both servers.  However, all external queries (eg uniwa.uwa.edu.au) will
query the 5.6.7.8 ONLY.  It will never query your primary server 1.2.3.4.
Thus if the secondary server 5.6.7.8 is down, your name resolution for
names outside domain.com will fail.

So you need the middle line

   .              1.2.3.4    ( )

This ensures that your primary server is queried for all names, not just
those in the domain.com domain.

Also note that domain.com need not have any connection to the DNS name of
your primary DNS server - it should be the name you want appended to
unqualified names.

Unless you are a guru at least as clued in as Pete Resnick (who has risked
life and limb in disassembling the DNR code in MacTCP to bring us this
valuable information and possibly saved the universe from the Empire) you
should always use a configuration like this:

   domain.com.    1.2.3.4    (*)
   .              1.2.3.4    ( )
   .              5.6.7.8    ( )

You have been warned.
   Peter.