DNS synonyms: multiple zones, one zone file

Solution 1:

Absolutely fine -- with one critically important caveat: You MUST use short names for your records.

foo                      IN    A      127.0.0.1             ; <-- This is fine.  
bar                      IN    CNAME  foo                   ; <-- This is fine.
baz                      IN    CNAME  foo.correctdomain.com ; <-- That's fine too.
@                        IN    A      127.0.0.2  ; <-- use @ for the base domain
                                                 ;     so it works everywhere

but

quux.correctdomain.com.   IN    A     127.0.0.1  ; <-- This will make BIND cry.
                                                 ; (because it's a bad name in
                                                 ;  synonymdomain.com's zone file)