I have an ESXi cluster that hosts several Windows Server VMs and around 30 Windows workstation VMs. Packet captures show a high number of ARP replies of the form: -sender_ip: VM IP -sender_mac: VM virtual MAC -target_ip: 0.0.0.0 -target_mac: Switch interface MAC The specific addresses aren't really a concern -- they're all legitimate and we're not having any problems with communications (most of the questions surrounding GARP and VMWare have to do with ping issues, a problem we don't have). I'm looking for an explanation of the traffic pattern in an environment that functions as expected. So the question is why would I see a high number of unsolicited ARP replies? Is this a mechanism VMWare uses for some purpose? What is it? Is there an alternative? EDIT: Quick diagram: [esxi]--[switch vlan]--[inline IDS]--[fw]--(rest of network) The IDS is complaining about these unsolicited ARPs. Several IDS vendors trigger on ARP replies without a prior request, or for ARP replies that have a target IP of 0.0.0.0. The target MAC in these replies is the VLAN interface on the switch. Capture points: -The IDS grabs the offending packets -The FW can see the same ones -A VM on the ESXi host does not see these, although there is an ARP request for a specific IP on the ESXi host that has source_ip=0.0.0.0 and source_mac=[switch vlan interface]. I can't share the captures, unfortunately. Really I'm interested in finding out if this is normal for an ESXi deployment.