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DNS proxy type=FWD records with failover

The Mikrotik DNS resolver supports static entries with type=FWD (forward). Combining this with the regex (and now the match-subdomain option since v7.6) allows you to forward queries for specific domains to a server. Unfortunately, the type=FWD resolver does not support any sort of failover.

No native failover for type=FWD

The first example below shows two FWD entries for the myad.loc domain. Each entry is configured to forward-to a different DNS server, as you would expect in a normal Active-Directory environment.

# the second FWD entry will never actually be used
/ip dns static
add name=myad.loc ttl=1m type=FWD forward-to=10.0.0.11 match-subdomain=yes 
add name=myad.loc ttl=1m type=FWD forward-to=10.0.0.12 match-subdomain=yes

Because there is no failover mechanism for type=FWD entries, the second entry will never actually get used, even if the forward-to target of the first entry is offline.

There is a workaround

Since the forward-to target can be a hostname, a workaround that has been discussed on the forums is to create multiple type=A records for a fake hostname, one for each DNS server you wish to forward to, and then set the forward-to target of the type=FWD record to this overloaded fake hostname. Here's a configuration using our myad.loc example domain:

/ip dns static
add name=myad.loc.rslv ttl=1m address=10.0.0.11
add name=myad.loc.rslv ttl=1m address=10.0.0.12
add name=myad.loc ttl=1m type=FWD forward-to=myad.loc.rslv match-subdomain=yes

 

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