I have been using the integrated DNS cache for years. I want to use a high speed out side DNS server for all my requests. Only if this cache is down I want to fall back on my internal email server as a cache. It does not seem to work that way. Looking at the outgoing port 53 udp requests Mikrotik load balances between primary and secondary caches rather then just falling over to the secondary. Is this the way its supposed to be?
Matt