Re: [nvrg-bof] What is Network Virtualization?

[Joe Touch <touch at ISI.EDU>]

Martin Stiemerling wrote:
...
> > IMO:
> > - ---
> > A _virtual network_ is a network composed of tunnels, virtual 
> > hosts, and/or virtual gateways. A tunnel is a link that 
> > encapsulates for control purposes, but reaches only the 
> > existing endpoints (this distinguishes it from how a native 
> > L3 uses a native L2). A virtual host is a network node that 
> > adds or removes headers, and has at least one tunnel endpoint 
> > in a given virtual network. A virtual gateway is a network 
> > node that does not add or remove headers, and has at least 
> > two tunnel endpoints in a given virtual network.
>
> I believe that this is the definition of a virtual network but not
> necessarily network virtualisation. The first sentence is already ruling
> out VLANs on ethernet (which could be one technique for network
> virtualization on that link layer). However, for virtual networks the
> defintion fits perfectly.

VLANs virtualize links, but not the endpoints. That makes them useful 
for their intended purpose, but defeats using just that mechanism to 
create a true virtual network. In particular, a VLAN cannot have a 
topology that doesn't match the underlying ethernet topology in certain 
ways - it cannot group endpoints to act as a single virtual endpoint, or 
fraction an endpoint to make it look like multiples, e.g.

Joe

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