Hi, I have always thought of GARP as a simple method by which a host can advertise to the local LAN a change in its MAC or IP address to speed up convergence and mitigate ARP timeout times. These kinds of GARPs would be replies.
So, what exactly is a GARP REQUEST and when would this technique be deployed?
Definiiton from website: A Gratuitous ARP could be a request or a reply. A Gratuitous ARP Request is the one where the Source and Destination IP address will be of the host itself which issues the request and is broadcast to the subnet and normally there will not be a reply.
Why would a host broadcast a GARP request such as this one and not want a reply....? I can see it being used as a method to test whether there is a duplicate address on the network, but it also has implications for NIC teaming....dont get it!
its just a mechanism that the server uses to announce a particular IP address to MAC address binding to other hosts on the same subnet. Correct? Each time it does so, it will announce a different MAC address - one for each of the NICs in the team. Correct?
Correct on both counts.
The reason is that you would have a loop if both NICs were active (assuming L2 adjacency between switches). So, the way to get away from the loop is to have access switches, like the Nexus 5000, that does vPC. Correct?
You would have the same MAC address listed on 2 physical switches which would cause a L2 loop. You are correct.
In the case of switches that allow you to 'stack' 2 physical switches into one like Nexus or 3750, the L2 Loop wouldn't occur as the physical entities are seen as one logical device.
What about the case where you have one dual-port NIC with the same uplink connections to the two switches and no vPC or stacking? Still be a loop?
It depends if the Dual-Port sends the same MAC address or different MAC address toward the switch network.
Same MAC Address, same explanation as above. Different MAC Address, it would work on any switching topology.