Re: [vnrg] Layering vs. virtualization

[Pedro Andrés Aranda Gutiérrez <[e-mail]>]

Hi,

Roland is really making an interesting point here. IMHO, we have to
say which layer we are talking about. Examples I see:

L1: DWDM; different lambdas are different virtual networks at L1

L2: 802.1q

L2.5:	the venerable ATM and MPLS nowadays

Cheers,/PA

On 29/07/10 10:20, Roland Bless wrote:
> Hi,
>
> I thought a little bit more on that topic, e.g., whether IP
> on top of Ethernet itself is a virtualization technique and I
> think that it is not - longer rationale below. First, I want to second
> what Aaron said: we should consider network technologies other
> than IP in the substrate as well as in the virtual network. So
> sometimes it is easier to think of some abstract substrate technology
> instead of IP as substrate.
>
> However, I think one difference between "layering" and virtualization
> is as follows:
> when you put another protocol layer on top, you usually have to
> do it in the "end-system"/at the end points, i.e., IP nodes are
> sitting at L2 end points whereas L2 nodes (e.g., switches) are
> transparent for L2 end points.
> Same in L3 (letting the control plane aside for this moment):
> routers as L3 network nodes are largely transparent for
> the end-systems (except for first/last-hop routers),
> i.e., a transport connection at L4 is normally
> terminated in L3 end-systems. So in this way neither IP is a virtual
> network on top of Ethernet nor is a TCP connection on top of IP, but I
> would consider IP as an overlay and abstraction technique (it mainly
> abstracts from different L2 networks in its substrate).
>
> In contrast, a virtualization technique in/at L2 involves mechanisms
> within the L2 nodes, e.g., support of VLAN tagging.
> A real network virtualization technique at layer 3 would require,
> e.g., partitioning of a L3 node/a router; lets consider that you are
> running a different protocol than IP in a partition.
> The "hard part" now is getting/demultiplexing from the substrate
> to the virtual parts of the router. There are various ways to do it
> depending on the substrate's capabilities.
> So using a dedicated physical L2 port would be one possibility,
> using VLANs over a shared L2 cable would be another. If the substrate
> is on higher layers MPLS LSPs or L3 tunnels etc. can be used.
>
> Sometimes it also helps to think on addressing the virtual resources
> from the control plane inside the substrate. Basically you have
> to address a VNet (denoting a specific virtual network),
> a Virtual Node, and a specific Virtual Interface inside the
> Virtual Node, e.g., in order to connect a substrate link/tunnel
> to a specific interface of this particular virtual node.
> However, it is not required that VNet-IDs, Virtual Node IDs,
> or Virtual Link/Interface IDs are literally carried in substrate
> data packets since there could be link-specific mapping techniques using
> available multiplexing mechanisms, e.g., VLAN-tags.
> In analogy one can denote such link-specific identifiers for VNets as
> "VNet-Tags". A VNet-Tag identifies a virtual link in a link-specific
> context. In absence of multiplexing support in the substrate, it may be
> required to use an explicit shim header that carries the
> VNet-Tag in order to allow proper demultiplexing of virtual networks on
> a shared substrate link.
>
> To keep a long story short: when talking about virtualization
> we must be specific which layer is actually virtualized or do we
> consider layer 3 only?
>
> Regards,
>   Roland
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-- 
Pedro A. Aranda Gutiérrez	Telefónica I+D
Technology Specialist		New Network Technologies
mailto: [e-mail]		C/Emilio Vargas,6
Tlf: [phone]            E-28043 Madrid

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