2013-01-21T15:52:35.989Z cpu1:2049)Tcpip_Vmk: 112: arp: 00:50:56:bd:3b:2b is using my IP address 172.30.0.213 on vmk1!The biggest challenge of course is to identify which ESXi host actually has a conflict and then taking a look at the logs to find the offending MAC Address and shutting them down yourself or with the help of a Network Administrator. Wouldn't it be great if we had an alarm to automatically notify us when a duplicate IP Address is detected? Well I am glad you asked and the answer is YES! :)
In addition to logging to the VMkernel logs, ESXi also logs this "observation" in /var/log/vobd.log which stands for the VMkernel Observation. These "observations" can provide critical identifying information in case of an error and is usually used during troubleshooting. In our case, we are seeing an intermittent network connectivity to our ESXi host which is in result of a duplicate IP Address. The really neat thing about these VOBs is that you can create vCenter Alarms when a specific VOB has been detected. I have shown an example of this before in my Detecting ESXi Remote Syslog Connection Error Using a vCenter Alarm article.
We can do exactly the same for detecting a duplicate IP Address for an ESXi host. The first thing we need to do is identify the VOB ID by looking in /var/log/vobd.log:
2013-01-21T15:02:07.513Z: [netCorrelator] 917174784727us: [esx.problem.net.vmknic.ip.duplicate] Duplicate IP address detected for 172.30.0.83 on interface vmk0, current owner being 00:50:56:bd:3b:2bWe can see the VOB ID for this is esx.problem.net.vmknic.ip.duplicate and this will be used in our vCenter Alarm trigger.
Step 1 - Create a new Alarm and specify a name, the Monitor type will be Hosts and Monitor For will be for a specific event:
Now that our alarm has been created, we will want to give this a test drive .... who can we ask? Well it just happens that I have a new user in my environment and I provisioned him a new VM which is already connected to the network. Let's hope he does not try to change the IP Address (because this never happens, right?)