Thursday, October 10, 2013

[vMotion] The reason of sending RARP packet after vMotion finished

Recently I read the article about How vMotion impacts the forwarding table, I found I didn't quite get understood the following sentence:
"The following article mentioned "When the VM-MAC1 is moved from Host 1 to Host 2 through vMotion process a Reverse ARP (RARP) is issued by Host2’s kernel module on behalf of the VM-MAC1."

After searching RARP and vMotion information, I know why RARP is used here. The answer is quoted from here:
"The goal for sending these frames is to make sure the physical switches in the network learns the location of the Virtual Machines. A physical switch does this learning by observing each incoming frame and make a note of the field called Source MAC Address. Based on that information the switches build tables with mappings between MAC addresses and the switch port where this address could be found."

So, in sum, physical switches and vSphere will update their forwarding table by receiving the broadcast address of RARP packet.

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