In previous article, I have discussed about historical
perspective of Network virtualization ( http://www.dhimanchowdhury.blogspot.com/2015/07/network-virtualization-101-nve-overlay.html
): how the need to share resources and induce flexibility and programmability
in network environment led to the series of research undertakings, e.g. MBone
project (Almeroth, C.K., 2000) – an experimental backbone project for carrying
IP “multicast” that was developed in 1994. If you have not read that article, I
suggest that you do: it will help you understand the development in network
virtualization and benefits thereof.
 |
| Figure 1. Timeline of Network Virtualization. |
This article is third in the “Network Virtualization 101”
series.
In the previous article, I presented a review of network programmability works
in four stages rather than in chronological order: three stages were discussed
in earlier section and the fourth “network virtualization” (NV) is presented
herein as follows.
The notion of “network virtualization” (NV) can be
understood as decoupling physical topology from logical topology (e.g., Overlay
networks) and as such, implementation does not require SDN. Similarly, the
common notion of SDN (separation of control plane and data plane) does not
require network virtualization. This distinction is important since many may be
confuse by the symbiotic nature in which network virtualization and SDN relate (Feamster,
N., Rexford, J. & Zegura, E., 2014):
- SDN as enabling technology: with the advent of cloud computing, service providers faced the challenge to share and isolate resources to multiple tenants in a way that make best use of available network infrastructure. A common method to share such isolation at VM level is to use overlay networks through protocols such as VxLAN and NVGRE. While VxLAN and/or NVGRE does not require SDN to implement but having the capability to provision the network for VxLAN and/or NVGRE from centralized server surely helpful. Another example of SDN as an enabling is Nicira’s network virtualization platform or NVP. The NVP framework implements Open vSwitch (a virtual switching platform), a controller and South bound API to facilitate network transport. The Open vSwitch is hardware agnostic and can be implemented in servers without the need for networking gears.
- Slicing or virtualizing an SDN: A hybrid switch for example implements both traditional protocol suits and OF (OpenFlow) agents and other flow control APIs. With appropriate arbitration mechanisms, network flow can be logically separated from other logical instances of network. Similarly, Flowvisor (a special purpose controller that works as transport proxy between OF agent and OF controller) allows slicing of network resources and delegates control of each slice to a different controller (Flowvisor, 2014).
From historical perspective, the work on Network
virtualization can be predated to the early days of MBone experiment. The MBone
otherwise known as “Multicast Backbone” is a virtual network built on top of internet.
It was invented by Van Jacobson, Steve Deering and Stephen Casner in 1992 as
part of an undertaking by IETF (Internet Engineering Task Force). In the early 1990s, majority of the routers
in the internet did not support IP Multicasting and packets were transported
through IP unicast. As a result one-to-many communication was difficult. The
solution was MBone or “Multicast Backbone” in which multicast function provided
by workstation running a daemon process known as “mrouted” (Almeroth, 2000). Workstation
running “mrouted” process is known as “mrouter” (essentially a multicast
router). These mrouters are than placed in special group of LAN or single LAN
that are multicast capable. The “mrouted” process received unicast-encapsulated
multicast packets on an incoming interface and then forwarded packets over the
appropriate set of outgoing interfaces. Connectivity among these machines was
provided using point-to-point, IP-encapsulated tunnels. Each tunnel is
connected two endpoints via one logical link. The routing decisions were made
using DVMRP (Distance Vector Routing Protocol) as shown the figure below.
 |
| Figure 2. MBone topology during the early years of its deployment. |
The DVMRP since then replaced by PIM (Protocol Independent
Multicast) helping MBone to be integrated with internet than its initial
attempts. For many years, network equipment supported the creation of virtual
networks, e.g. VLAN which allows the creation of multiple logical networks on
top of physical topology. But such network virtualization is limited to L2
network segments and impedes on the deployment of new technologies traversing
across the network. To overcome this, researchers and practitioner resorted to
running overlay networks which allows endpoint nodes to run their own control
plane and forward data traffic and control-plane message across the networks
traversing multi hop L3 networks. The
MBone (for multicast) and 6Bone (for IPV6) are example of such overlay network
virtualization. In the previous article, I discussed example of overlay network
architecture and some of the protocol used for tunneling and will explore this
further in the succeeding articles about network virtualization configurations.
The complete survey of network virtualization is cumbersome, however, the historical
perspective I am presenting herein, though brief, is important in the research
of network programmability (SDN) and in the gradual development of programmable
and dynamic network systems. It is to be noted both SDN and network
virtualization is tightly coupled despite their distinctions. Programmable
network (i.e. SDN) often presume “network virtualization” as an integral part
to share network infrastructure for multi-tenant services supporting logical
network topologies that differ from physical network. The early overlay network
that is essential in evaluating and understanding “network virtualization”
often used dedicated nodes running special protocols. The notion of such early
day overlay network soon expanded to include any host computer that run special
application in hope of supporting peer to peer file sharing application (e.g.
Napster; Wikipedia, 2015). The research on peer to peer networking reignited
interest and research works in the development of robust overlay network
technologies. An example of such work is “Resilient Overlay Networks” (Andersen
et al., 2015) in which a small number of network nodes form overlay network
detecting network failure and recovering quickly from network issues and
performance problem. Since overlay network does not require any special
equipment (unlike Active network; please refer to my previous article),
researchers began building experimental infrastructure like Planetlab (Peterson
et al., 2002) to support wider research works on network virtualization. Interestingly,
PlanetLab itself was a form of
“programmable router/switch” active networking, but using a collection of servers
rather than the network nodes, and offering programmers a conventional
operating system (i.e., Linux) (Feamster, N., Rexford, J. & Zegura, E.,
2014). The project of GENI (GENI, 2015) took this notion of programmable
virtual network infrastructure to next level supporting much large scale
national experimental for research in networking and distributed system.
 |
| Figure 3. GENI - The vast experimental virtualized network infrastructure project (GENI, 2015). Figure (Courtsey, GENI, 2015). |
If you are interested in experimenting your concept in a
virtualized network infrastructure, please visit http://groups.geni.net/geni/wiki/GENIConcepts
and join the project.
Considering the project like GENI, one can easily perceive
the potential of network virtualization. Some researchers argued that network
virtualization is key to next generation internet architecture. In the first
article of this series, discussing about NVE (Network Virtualization
Environment) I explored the theoretical connotations from various scholars
regarding the need for next generation internet and service provider network in
which multiple network architectures can coexist at the same time (each optimized
for different applications or requirements, or run by different business
entities), and evolve over time to meet changing needs (Feamster, N., Rexford,
J. & Zegura, E., 2014; Carapinha & Jiménez, 2009; Chowdhury & Boutaba,
2009; Chowdhury & Boutaba, 2008).
I hope this brief overview of NV (Network Virtualization) is
helpful in understanding the difference and dependencies between network
virtualization and SDN and the importance of network virtualization in future
network design. You will find the basic understanding helpful in the succeeding
articles about network architecture and configurations.
In the next article, I will extend the notion of Network Virtualization to VNF (Virtual Network Function) and NFV (Network Function Virtualization). Please stay tune and follow me at linkedin (https://www.linkedin.com/in/dhiman1 ), twitter @dchowdhu ( https://twitter.com/dchowdhu ) and
google plus (https://plus.google.com/u/0/+DhimanChowdhury/posts
). You may also subscribe to all these feeds through Agema System’s linkedin
page at https://www.linkedin.com/company/agema-systems-inc?trk=top_nav_home
Reference
[Almeroth, C.K., 2000] Almeroth, C.K., 2000. The Evolution of Multicast: From the MBone
to Interdomain Multicast to Internet2 Deployment. IEEE Network. Available
online at http://www.cs.ucsb.edu/~almeroth/classes/F05.276/papers/evolution.pdf
.
[Andersen et al., 2001] Andersen, D. G., Balakrishnan, H.,
Kaashoek, M. F. & Morris, R., 2015. Resilient
Overlay Networks. In Proc. 18th ACM Symposium on Operating Systems Principles
(SOSP), pages 131–145, Banff, Canada, Oct. 2001.
[Carapinha, J. & Jiménez, J. 2009] Carapinha, J. & Jiménez,
J. 2009. VISA '09 Proceedings of the 1st
ACM workshop on Virtualized infrastructure systems and architectures. The
ACM Digital Library.
[Chowdhury, K.M.M.N. & Boutaba, R., 2008 ] Chowdhury,
K.M.M.N. & Boutaba, R., 2008. A
Survey of Network Virtualization. Technical Report CS-2008-25. University
of Waterloo.
[Chowdhury, K.M.M.N. & Boutaba, R., 2009 ] Chowdhury,
K.M.M.N. & Boutaba, R., 2009. Network
Virtualization: State of the Art and Research Challenges. IEEE
COMMUNICATIONS MAGAZINE.
[Clark et al., 2006] Clark, D., Lehr, B., Bauer, S.,
Faratin, P., Sami, R. & Wroclawski, J., 2006. Overlay Networks and the Future of the Internet. Communications
& Strategies, no. 63, 3rd quarter 2006, p. 109.
[Feamster, N., Rexford, J. & Zegura, E., 2014] Feamster,
N., Rexford, J. & Zegura, E., 2014. The
Road to SDN: An Intellectual History of Programmable Networks. ACM Queue,
2014.
Flowvisor, 2014. Flowvisor. Atlassian Confluence Open Source
Project: University of Stanford. Available online at https://openflow.stanford.edu/display/DOCS/Flowvisor
[Feamster et al., 2004] Feamster, N., Balakrishnan, H., Rexford,
J., Shaikh, A. & van der Merwe, J., 2004. The Case for Separating Routing from Routers. SIGCOMM’04 Workshops,
Aug. 30-Sept. 3, 2004, Portland, Oregon, USA.
[GENI, 2015] GENI: Global Environment for Network
Innovations. Available online at http://www.geni.net/.
[Peterson, et al., 2002] Peterson, L., Anderson, T., Culler,
D. & Roscoe, T., 2002. A Blueprint
for Introducing Disruptive Technology into the Internet. Planet Lab.
Proceedings of the First ACM Workshop on Hot Topics in Networks (HotNets-I),
Princeton, NJ, October 2002.
[Wikipedia, 2015].
Wikipedia, 2015. Napster. Wikipedia: The free Encyclopedia. Available online at
https://en.wikipedia.org/wiki/Napster
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