Information Technology Reference
In-Depth Information
A MAC address is changed.
A NIC team failover or failback has occurred.
Turning Off Notify Switches
h e Notify Switches option should be set to No when the port group has VMs using Microsoft
Network Load Balancing (NLB) in Unicast mode.
In any of these events, the physical switch is notii ed of the change using the Reverse Address
Resolution Protocol (RARP). RARP updates the lookup tables on the physical switches and offers
the shortest latency when a failover event occurs.
Although the VMkernel works proactively to keep trafi c l owing from the virtual network-
ing components to the physical networking components, VMware recommends taking the fol-
lowing actions to minimize networking delays:
Disable Port Aggregation Protocol (PAgP) and Link Aggregation Control Protocol (LACP)
on the physical switches.
Disable Dynamic Trunking Protocol (DTP) or trunk negotiation.
Disable Spanning Tree Protocol (STP).
Virtual Switches with Cisco Switches
VMware recommends confi guring Cisco devices to use PortFast mode for access ports or PortFast
trunk mode for trunk ports.
Using and Confi guring Tra c Shaping
By default, all virtual network adapters connected to a vSwitch have access to the full amount
of bandwidth on the physical network adapter with which the vSwitch is associated. In other
words, if a vSwitch is assigned a 1 Gbps network adapter, then each VM coni gured to use the
vSwitch has access to 1 Gbps of bandwidth. Naturally, if contention becomes a bottleneck hin-
dering VM performance, NIC teaming will help. However, as a complement to NIC teaming,
you can also enable and coni gure trafi c shaping. Trafi c shaping establishes hard-coded limits
for peak bandwidth, average bandwidth, and burst size to reduce a VM's outbound bandwidth
capability.
As shown in Figure 5.41, the Peak Bandwidth value and the Average Bandwidth value are
specii ed in kilobits per second, and the Burst Size value is coni gured in units of kilobytes. The
value entered for Average Bandwidth dictates the data transfer per second across the virtual
vSwitch. The Peak Bandwidth value identii es the maximum amount of bandwidth a vSwitch
can pass without dropping packets. Finally, the Burst Size value dei nes the maximum amount
of data included in a burst. The burst size is a calculation of bandwidth multiplied by time.
During periods of high utilization, if a burst exceeds the coni gured value, packets are dropped
 
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