Private / public DNS coexistence

[Olivier Kurzweg]

Hello,
We are using a private DNS hierarchy, whose root is "priv." (instead of
"com." or "org." for instance). Our site in London is in zone
"london.priv.", and the one in Paris is in "paris.priv.". Paris is
authoritative for zone "priv."
Paris and London both access to the Internet through their own DMZ. A DNS
cache on each DMZ resolves Internet-based names.
We would like to have the following behaviour for DNS:

----------                                ------------
  DMZ    ¦                                ¦  DMZ     ¦
  London ¦                                ¦  Paris   ¦
----------                                ------------
     ^                                          ¦
     ¦ forward queries                          ¦
     ¦ if not inside "priv."                    ¦
------------          ------------        ------------
  LAN      ¦          ¦   VPN    ¦        ¦   LAN    ¦
  London   ¦--------->¦          ¦------->¦   Paris  ¦
------------          ------------        ------------
        resolve (not forward !)
        if inside "priv."

Is there any possibility to obtain such a behaviour with bind? If we use a
forward for "priv." addresses instead(zone type forward), the server at
Paris will have to replicate the zones of all our sites.
Does anybody knows a workaround?

Any help would be greatly appreciated.
Cheers,

*************
Olivier Kurzweg
mail: okurzweg at siticom.co.uk
mail alias: olivier.kurzweg at mail.dotcom.fr
+44 (0) 171 766 5217 - ext: 6311