Apple Mac computers lose connectivity to on-premise Exchange server

Every day we experienced many of our Macs losing their connection to the mail server which happened to be a Microsoft SBS 2008 server. For many months the solution was to connect to the public wireless connection that was OK for the users but it was just a workaround. Connectivity would be sporadic and having the Macs connected to the LAN over the wire and to the public wireless connection wasn’t a good long term solution.

After much troubleshooting I figured out that the configuration of their DNS and DHCP servers was incorrect. Research and testing revealed that Macs use Autodiscover to connect to the Exchange server. Internal DNS didn’t have the autodiscover records required by internal Exchange clients. And it didn’t matter what client – Entourage, Apple Mail, Outlook for Mac – they all lost connectivity quite often and a random times. Once was resolved but adding the proper records there was one other problem.

DHCP was configured to assigned the SBS server AND and external DNS server for DNS. Once that was rectified by setting DHCP to assign just the SBS server as the DNS server and running DNS Bench to determine the fastest DNS servers for the office and setting them as the forwarders, the Macs maintained stable connectivity to the Exchange server. Finally!

Why was this the case? The Macs need Autodiscover records to be set up correctly in DNS. That’s why connecting over public wireless connection worked. The external DNS servers had Autodiscover records set up correctly for external clients. Luckily this worked for their environment as a band-aid. When the internal one wasn’t configured correctly the Macs could never connect to the Exchange server using the internal DNS server to resolve hostnames.

Why was it sporadic? I chalk it up to the sometimes slow DNS name resolution of the SBS server. If it didn’t respond quick enough, it would force the Macs to use the external DNS server for name resolution and would work, but if the SBS server did respond in time, they would lose connectivity.

So fixing both was necessary – DHCP to only assign the SBS server as the internal DNS server and for DNS to be configured with the correct Autodiscover records.

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This network issue threw me for a loop

I got sent to a network problem for one person in a office and some troubleshooting took place as well as some remediation steps. Basically the user had no network access all of a sudden. The computer had already been rebooted (the first thing IT people seem to recommend, right?)

The network card was removed from device manager and reinstalled. At that point I was dispatched to the client. I tried some basic stuff – swapped network cables. That didn’t work. Rebooted the switch. Forced the NIC into 100 Mbps Full – nope. 100 Mbps Half – nope. 1 Gbps – nope, nope. Scanned for malware. None found. I started working on it in the server room and after updating the NIC drivers, I got internet. Cool! It’s fixed.

Then I moved it back to the user’s desk and no internet again. Hmm…I guess it’s the cable drop between the network closet and the office. Temporary solution – move his computer to another desk. So we move all the components – PC, monitors, cables, keyboard, etc. And???

NO NETWORK AGAIN? Okaaay

Moved to another office on a different switch. Still no network. What? Back in the server room it started getting spotty network connectivity. Weird. Contacted Dell support and my manager. Ran a BIOS update and did a clean uninstall of the NIC from Device Manager. Reinstalled the NIC with fresh drivers from Dell. Seems to have network connectivity. Moved it back to the temporary desk. No network!!!

What is going on??

I’m scratching my head trying to figure it out. So on a whim, I decided to try 100 Mbps Full and I got network! Hooray! 1 Gbps doesn’t seem to work and Auto-negotiate doesn’t work either. So in the end it took a BIOS update, NIC driver refresh, and forcing the NIC to connect at 100 Mbps.

Nothing changed as far as I can determine. No updates were installed and the user didn’t change anything. Why it didn’t work all of sudden? Who knows? I’m just glad it’s working!