Why load sharing
With virtualization, network and server domains converge; there are usually multiple vendors for server, NIC, storage, and networks. A typical example is using Nexus 1000v which is a Cisco product, embedded in ESX which is VMware, utilizing an HP NIC, and interacting with NAS which is yet another vendor.
Why load sharing? It is high desirable to have redundant uplinks from an ESX host for high availability. In addition, load sharing over redundant uplinks improves performance and utilization. So what are the load sharing options from the host?
A fundamental design is how traffic flows to and from VM to the rest of the network. In this example, VMs reside in ESX, but the concept is the same for any virtualization host interacting with the network.
There have been numerous vendor documents, often covering a certain aspect in detail, occasionally conflicting and confusing as technologies have been evolving. I posted earlier about load sharing mainly on Nexus switch side. Scott Lowe has a series of excellent articles on the topic. Why the summary here? I found it necessary to organize multiple concepts around host load sharing under a simple framework to make it easier to understand and apply.
Options
The following table summarizes common load sharing options, from the least desirable to the most.
click to see full size image of the summary.
Additional Considerations - LACP
The last two options require some clarification. Without Nexus 1000v, VMware does not support dynamic DHCP. Therefore VMware documentation usually specifies “mode on” as the recommended configuration. Cisco definitely supports dynamic LACP, although earlier Nexus 1000v releases may have had some LACP specific bugs. The latest Nexus 1000v Release 4.2(1) SV1(4) contains many fixes, but is to be proven in a production system, it also has the additional benefit of LACP offload from VSM to VEM. If you know of more recent developments or road map, please kindly let me know.
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