Wile E. Coyote

One of the classic moments in a Road Runner cartoon is Wile E. Coyote pursuing the Road Runner into a cloud of dust. Wile E. Coyote starts to suspect that there is something wrong, but remains suspended until the moment of realization that he is no longer on the road, but is instead suspended in mid-air over a chasm.

In the cartoon, the dust cloud allows Wile E. Coyote to temporarily defy the laws of physics by hiding the underlying physical topography. The Road Runner is under no such illusion - by leading the Road Runner is able to see the road ahead and stay on firm ground.

Example of an SDN solution with tunnels

Current network virtualization architectures are built on a similar cartoon reality - hiding the network under a cloud (using an overlay network of tunnels) and asserting that applications will somehow be insulated from the physical network topology and communication devices.

The network virtualization software used to establish and manage the overlay are a form of distributed computing system that delivers network connectivity as a service. Vendors of network virtualization software that assert that their solution is "independent of underlying hardware" are making flawed assumptions about networking that are common to distributing computing systems and are collectively known as the Fallacies of Distributed Computing:

1. The network is reliable
2. Latency is zero
3. Bandwidth is infinite
4. The network is secure
5. Topology doesn't change
6. There is one administrator
7. Transport cost is zero
8. The network is homogeneous

This article isn't intended to dismiss the value of the network virtualization abstraction. Virtualizing networking greatly increases operational flexibility. In addition, the move of complex functionality from the network core to edge hardware and virtual switches simplifies configuration and deployment of network functions (e.g. load balancing, firewalls, routing etc.). However, in order to realize the virtual network abstraction the orchestration system needs to be aware of the physical resources on which the service depends. The limitations of ignoring physical networking are demonstrated in the article, Multi-tenant performance isolation, which provides a real-life example of the type of service failure that impacts the entire data center and is difficult to address with current network virtualization architectures.

To be effective, virtualization architectures needs to be less like Wile E. Coyote, blindly running into trouble, and more like the Road Runner, fully aware of road ahead, safely navigating around obstacles and using resources to maximum advantage. In much the same way the hypervisor takes responsibility for managing limited physical resources like memory, CPU cycles and I/O bandwidth in order to deliver compute virtualization; the network virtualization system needs to be aware of the physical networking resources in order to integrate them into the virtualization stack. The article, NUMA, draws the parallel between how operating systems optimize performance by being aware of the location of resources and how cloud orchestration systems need to be similarly location aware.

One of the main reasons for the popularity of current overlay approaches to network virtualization has nothing to do with technology. The organizational silos that separate networking, compute and application operational teams in most enterprises make it difficult to deploy integrated solutions. Given the organizational challenges, it is easy to see the appeal to vendors creating overlay based products that bypasses the network silo and deliver operational flexibility to the virtualization team - see Network virtualization, management silos and missed opportunities. However, as network virtualization reaches the mainstream and software defined networking matures, expect to see enterprises integrate their functional teams and the emergence of network virtualization solutions that address current limitations. Multi-tenant traffic in virtualized network environments, examine the architectural problems with current cloud architectures and describe the benefits of taking a holistic, visibility driven, approach to coordinating network, compute, storage and application resources.