Review/Perspective: Virtualization Technologies

2.1.h Describe chassis virtualization and aggregation technologies

  • 2.1.h [i] Multichassis
  • 2.1.h [ii] VSS concepts
  • 2.1.h [iii] Alternative to STP
  • 2.1.h [iv] Stackwise
  • 2.1.h [v] Excluding specific platform implementation

Multi-chassis virtualization allows for multiple networking devices to aggregate into a single logical device increasing total forwarding capacity and including inherent hardware redundancy.

VSS – Virtual Switching System is a virtualization technology that allows two Cisco 6500 switches to act as a single logical virtual switch.  This increases operational efficiencies and scales bandwidth up to 1.4 Tb/s, this is similar to stackwise however VSS is limited to two physical chassis connected together.

Alternatives to STP

All of the following technologies allow aggregate links between two or more devices to be in a forwarding state outside negating or replacing the effects of running traditional spanning tree removing the possibility of blocked ports.

Virtual Port Channel  – enables loop free topologies where STP is no longer involved in maintaining network topology and no links between access and aggregation are blocked.  STP does still run however it’s only run on the primary vPC device where the secondary device only transparently forwards BPDUs back/fourth between the primary and the rest of the network.
TRILL – Transparent Interconnection of Lots of Links – TRILL replaces STP as a mechanism to find loop-free trees within Layer 2 broadcast domains to enable scaling.
FabricPath – also known as Layer 2 multipathing allows bandwidth between access and aggregation layer to be scaled beyond what is possible with traditional spanning tree or vPC

StackWise – is a switching technology that allows multiple cisco switches to aggregate into a single switching backplane.  StackWise cables connect the individual switches connecting the switching backplane to each other device.  This allows for increased port density.  The switches are also viewed logically as a single device in the CLI as far as management is concerned.  You can still access the switches individually if needed as well.  StackWise assigns a master switch where all management and configurations are defined and the other connected switches take on a slave mode where they inherit the configurations defined within the master.

Excluding specific platform implementation means when testing new feature functionality, underlying specific platform limitations are not taken into account.  for example an IOS feature that’s being tested in the IOS may function differently when installed on a 3560 as opposed to a 2960, hardware differences and limitations are not taken into account when they exclude platform implementations, they are only testing the functionality of the feature within the IOS image itself.


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