Confusing behavior in Exchange 2007/2010 when changing Hub Transport DNS configuration
I recently ran into a configuration issue in Exchange 2007/2010 that left me scratching my head in bewilderment. After noticing some DNS resolution issues between several hub transport servers I began looking at individually and manually configuring DNS resolution settings on specific Exchange servers. In ESM I went to “Server Configuration > Hub Transport” and viewed the properties of each server. On the “Internal DNS lookups” and “External DNS lookups” tabs you get the option to choose either the DNS configuration from a specific network adapter or manually enter the DNS servers to use.
To save time, I began using the drop down selection of specific network adapters to grab the DNS servers I wanted. However, there is an important “gotcha” here that is not indicated in the GUI or anywhere else that I’ve seen. Basically what is happening is that when you use the drop down NIC selections to grab DNS, what you are doing is querying the NICs of the server on which you are running ESM. So what happened in my case is that incorrect DNS servers were being assigned to remote Exchange servers because I assumed that the NICs being listed in the drop down were the NICs physically installed on the remote server for which I was viewing the properties. Big mistake!
I started noticing events in the logs complaining about inability to resolve DNS hosts. Once I started investigating this it dawned on me that the names of the NICs in the drop down listing never changed as I viewed the properties of different servers. It just happened that the NIC I chose did not have any DNS servers configured, so I was basically configuring those specific Exchange servers with no DNS at all on the hub transport DNS resolution configuration.
To resolve the issue, I manually specified the DNS servers to use for each specific Exchange server. That completely resolved the problem and got mail flowing again.
Just kind of curious why Microsoft would allow you to manage remote servers from one location/instance of ESM but only show you the NICs on the local server when configuring remote server hub transport properties.