Re: [vnrg] Logical vs. virtual

[Joe Touch <[e-mail]>]

(again, speaking as an individual participant):

On 7/15/2010 9:36 AM, Didier Colle wrote:
> Dear Joe, all,
>
>> I tend to think of a logical device as not really adding to the
>> capabilities of a physical one, though, whereas a virtual one seems to
>> (at least to me).
>
> Please explain. What capabilities are you referring to?
> So far, I think most people on the list have expressed a virtual network
> having the same or a subset of the capabilities of the network. Do you
> agree with that? And remains that statement true for a virtual device
> rather than virtual network?

A physical network can't be relocated while running. A virtual one can.
A physical network doesn't ensure separation from other physical 
networks; a virtual one should, IMO.

>  From your previous post today, these capabilities are not apparent.
>> 1.c. what is the characteristic behavior/capability of the
>> resulting system?
>>
>> I think that the defining characteristic of a VN is that it allows an
>> existing network to concurrently emulate another, distinct and
>> separate network.
 >
> Is that a characteristic/capability of the virtual network (VN) or of
> the underlying existing network?

The VN. Without the VN, no such emulation would occur, IMO.

>> Maybe these are really just two aspects of a single thing, i.e., I
>> would differentiate between:
>>
>> - a device which does not map 1:1 to a physical entity
>> (could be a part of one, a group of many, or a group of parts)
>>
>> - a device which provides supports virtual networking
>>
>> Since we call the latter "virtual networking" (the name of this RG), I
>> would propose that the latter would be the virtual device, and the
>> former be the logical one.
>
> Hmm... so the resulting question is: What is virtual networking? ;-)

I had proposed a definition - which is a network composed of tunnels. 
The rest, IMO, is largely in support of that one distinguishing 
characteristic.

>> I don't think of it as a 'specialized form', but rather the fact that
>> a single virtual router CANNOT be mapped onto a single physical device
>> with no other logical components.
>>
>> I.e., a virtual router needs a base router to connect to the links of
>> the tunnel. A virtual host needs a base router (as well) for the same
>> reason.
 >
> Really? In your previous post you said: "A virtual link is the easiest
> to define - it is a tunnel over some existing network path, i.e., with
> an additional layer of encapsulation that is used solely for the VN, but
> which is otherwise not needed. A virtual router forwards packets between
> virtual links. " So, virtual link is encapsulated (e.g., by tagging with
> a VLAN-ID?) to allow multiplexing: is this something the virtual router
> cannot do (although invisible to the user/owner of the virtual router)?

A virtual router can encapsulate, but doesn't know what to do with the 
encapsulated packet, IMO. At some point the packet needs to go out a 
physical interface, and I don't think virtual routers own any physical 
interfaces.

> Do you need for that another "base" router?

No; that's what I needed the base router for in the first place.

Joe