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How to control DNS resolution for an external domain

I recently had a situation come up where I needed to change the traffic flow on my LAN for Outlook Anywhere clients that were going out to the internet to connect to our email provider (outlookanywhere.domain.com). Our provider is also accessible internally via a disparate and complicated network so the internet method was preferred due to less complexity. The Outlook Anywhere public facing servers were having problems, denying my client connections, so I needed to force the connections internally.

Caveats:

  • I still want my clients to be able to access Outlook Anywhere outside the office so I can’t disable it or change the address it connects to
  • HOSTS files are unmanageable
  • I do not own the namespace of the servers that Outlook Anywhere connects to
  • I will have to statically route to each destination in the provider’s namespace (from my core network) as our networks are connected but not well routed

To pull this off there are a few available options:

  • Leverage conditional forwarders to the affected namespace
  • Create a new primary DNS zone for this namespace, add the host record I need to redirect
  • Create a new primary DNS zone for each FQDN that I want to redirect

The first option is the simplest, I could just route all of the requests to this domain directly to its internal DNS servers. The problem with this is that I’ll have to also statically route to every possible server/host in that network that users might access. There are too many.

The second option would also work but then I’d need to create A records for any other hosts in that namespace or clients would be unable to resolve them.  The routing problem exists here too so this is a bad option for me.

The third option is the money ticket. Using this method I can simply create a new forward lookup zone for outlookanywhere.domain.com and in that zone create a nameless A record with the internal IP of that server. Easy. I still have to statically route to this server but all other public facing resolutions will continue to work without issue. This solution will work for any external namespace if you need to redirect your internal clients somewhere else.

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