It’s Christmas, and a silent time at my customers, so I finally got time to sit down and troubleshoot an annoying Error event at a 2008 DC. It was the famous Event 10009 from the DistributedCOM source.

DCOM was unable to communicate with the computer using any of the configured protocols.

As usual, I began at Bing and Google, but the results was blank or just not relevant for this case, so the next step was to begin troubleshooting hands on.

Ping form the server generating the events looked fine.

Ping from the server that the DC insisted on being unable to communicate with, looked fine.

So, just for fun, I did a trace from the server not responding, and got this unexpected result

What on earth did just happen? A quick check at the network settings made the world much clearer.

I had typed the subnet mask a bit too fast when configuring the server. Notice the /32 mask there. All my traffic was routed to the firewall and router in the subnet before it actually reached its goal.

After correcting this error, Event ID 10009 was gone, and I become a few bits smarter. Happy New Year.