Flow-Based Hashing; Control Interface Prioritization; Spanning Tree Protocol; Vsm Design - Cisco Nexus 1000V Series Deployment Manual

With source-based hashing, a MAC address can move between interfaces in a PortChannel under the following
conditions:
The virtual machine moves to a new VMware ESX or ESXi host (VMware VMotion, VMware High Availability,
●
etc.)
A PortChannel link fails, causing recalculation of the hashing
●
A link is added to the PortChannel, causing rehashing
●
The following Cisco Nexus 1000V Series algorithms can be classified as source-based hashes:
Virtual port ID
●
Source MAC address
●
VLAN
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Source IP address
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Flow-Based Hashing

Flow-based hashing enables traffic from a single MAC address to be distributed down multiple links in a PortChannel
simultaneously. Selecting a flow-based hash can potentially increase the bandwidth available to a virtual machine
and increase the utilization of the uplinks in a PortChannel by providing more granular load balancing.
Flow-based hashing algorithms are any algorithms that use the following to hash:
Packet destination
●
Layer 4 port
●
Combinations of source address, destination address, and Layer 4 port
●

Control Interface Prioritization

The control interface is a critical link between the VSMs and VEMs. The control interfaces are the most important
interfaces in any Cisco Nexus 1000V Series implementation. Special care needs to be taken to provide the control
interfaces on both VSMs and each VEM with a minimum level of bandwidth. Expect each control interface to require
a minimum of 10 KB of per-second bandwidth. Extended bursts of network traffic, such as VMware VMotion events,
could starve the control interface.

Spanning Tree Protocol

Spanning Tree Protocol goes through a series of states on each interface as it tries to build the network tree. This
process causes downtime on each interface when Spanning Tree Protocol needs to converge. This process is
unnecessary for ports connected to the Cisco Nexus 1000V Series. By using the PortFast feature on a switch port, a
Cisco switch can suppress the progression of Spanning Tree Protocol states and move straight to a forwarding state.
PortFast is configured per interface and should be enabled on interfaces connected to a VEM

VSM Design

The VSM is a standard virtual machine that is deployed in the same way as other virtual machines. It does have
specific design considerations that must be followed.

Virtual Machine Design

The Cisco Nexus 1000V Series VSM virtual machine has several basic considerations for deployment. Each VSM in
an active-standby pair is required to run on a separate VMware ESX host. This requirement helps ensure high
availability if one of the VMware ESX servers fails. You can also use the anti-affinity option in VMware ESX to help
keep the VSMs on different servers. This option does not prevent the VSMs from ending up on the same server; anti-
© 2009 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information.
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