I wanted to take a few minutes to point out the 17 different load balancing algorithms available when distributing traffic from a VMware vSphere ESX host to a network of clustered upstream switches. Normally I don’t write blogs on such short topics but this one has a little story behind it.

This week I am at VMworld 2010 attending a lot of great sessions, meeting new people, and reconnecting with some really awesome people I know in the industry.

I decided to drop into a session on Virtual Networking by Nicholas Weaver who is a vSpecialist at EMC, whom I know from conversations with him on twitter (@lynxbat) and his blog. One thing I learned today is that if you enter a session taught by Nicholas you had better be prepared to be called out to answer a question or provide commentary.

During the session Nick called me out several times in front of his packed audience to promote my blog. Thank you for that Nick, I really appreciate it, you didn’t need to do that. You did a great job with the session and deserve all the attention for it.

At one point Nick was presenting a slide on the Nexus 1000V and its capabilities to provide very granular load balancing. Nick stated to the audience that he believed the Nexus 1000V had 17 different possible load balancing algorithms, but had called me out again for verification. Caught a little off guard and unprepared, for some reason the number 15 came to my mind, so I responded: “Yeah, pretty close”. Not that a difference of 2 really matters, but nonetheless in such a technical session of paying participants you want to get every detail correct.

After Nick moved on to other slides I pulled out my laptop to double check, and sure enough, Nick was 100% correct that it is 17 different algorithms the Nexus 1000V can use to load balance traffic (when using a port channel uplink).

So, this post is dedicated to Nicholas Weaver and his packed VMworld session. Great job with the session Nick. I think its great to see non-Cisco presenters touting the virtues of Nexus 1000V and advocating its deployment.

Below are the 17 different load balancing algorithms you can choose from when using a port channel uplink from Nexus 1000V, preceded by a simple use case diagram. Each algorithm is telling the Nexus 1000V which fields to look at to determine what constitutes a flow and calculate a hash that determines which physical port channel member link will carry that flow.

nexus 1000v load balancing

  • dest-ip-port—Loads distribution on the destination IP address and L4 port.
  • dest-ip-port-vlan—Loads distribution on the destination IP address, L4 port, and VLAN.
  • destination-ip-vlan—Loads distribution on the destination IP address and VLAN
  • destination-mac—Loads distribution on the destination MAC address.
  • destination-port—Loads distribution on the destination L4 port.
  • source-dest-ip-port—Loads distribution on the source and destination IP address and L4 port.
  • source-dest-ip-port-vlan—Loads distribution on the source and destination IP address, L4 port, and VLAN.
  • source-dest-ip-vlan—Loads distribution on the source and destination IP address and VLAN.
  • source-dest-mac—Loads distribution on the source and destination MAC address.
  • source-dest-port—Loads distribution on the source and destination L4 port.
  • source-ip-port—Loads distribution on the source IP address.
  • source-ip-port-vlan—Loads distribution on the source IP address, L4, and VLAN
  • source-ip-vlan—Loads distribution on the source IP address and VLAN.
  • source-mac—Loads distribution on the source MAC address.
  • source-port—Loads distribution on the source port.
  • source-virtual-port-id—Loads distribution on the source virtual port ID.
  • vlan-only—Loads distribution on the VLAN only.

The algorithm that I recommend most is source-dest-ip-port, where the Nexus 1000V will look at the source and destination IP address and TCP/UDP port numbers to constitute a flow and make a hashing decision. Given the inspection up to Layer 4, this generally provides the most granular flow definitions and therefore closer to 50/50 Even Steven load balancing than the other methods. As shown in the diagram above, both VM1 and VM2 might have multiple flows each with different destination IP addresses or TCP/UDP port numbers, and therefore each flow could be distributed on separate physical links.

The default algorithm is source-mac. This setting will take all flows from a VM (assuming a single source MAC address) for placement on a single physical link within a port channel.

Configuration Example:

Nexus-1000V(config)# port-channel load-balance ethernet src-dest-ip-port

Link to Configuration Documentation