Network Working Group K. Kumaki
Internet-Draft KDDI Corporation
Intended status: Informational P. Mohapatra
Expires: July 15, 2014 Cumulus Networks
D. Meyer
Brocade
K. Varadhan
Z. Ali
Cisco Systems
January 11, 2014
A Virtualized Network Element Framework
draft-kumaki-vnef-02
Abstract
This document outlines a new architectural paradigm of virtualizing
the service provider networks and its associated engineering
requirements. The framework is referred to as the virtual network
element framework (VNEF) in the document.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Use Case 1: Operational Independence . . . . . . . . . . . 4
1.2. Use Case 2: Network Redundancy . . . . . . . . . . . . . . 5
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Problem Statement and Related Areas . . . . . . . . . . . . . 6
4. Reference Model . . . . . . . . . . . . . . . . . . . . . . . 7
5. Applications . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Network Wholesale Services . . . . . . . . . . . . . . . . 8
5.2. On-demand Network Services . . . . . . . . . . . . . . . . 8
6. Requirement Details . . . . . . . . . . . . . . . . . . . . . 9
6.1. Dynamic binding - On-demand Service Creation . . . . . . . 9
6.2. Control Plane/Routing Layer Separation . . . . . . . . . . 9
6.3. Data Plane Separation . . . . . . . . . . . . . . . . . . 9
6.4. Separate Operation of Services . . . . . . . . . . . . . . 9
6.5. QoS/SLA . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.6. Load Balancing . . . . . . . . . . . . . . . . . . . . . . 10
6.7. Scale . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Element Virtualization . . . . . . . . . . . . . . . . . . 10
7.2. Network Virtualization . . . . . . . . . . . . . . . . . . 11
7.3. Service Identification . . . . . . . . . . . . . . . . . . 13
8. Comparison with Other Technologies . . . . . . . . . . . . . . 13
8.1. VRF . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.2. Network Virtualization Over L3 . . . . . . . . . . . . . . 13
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
11. Security Considerations . . . . . . . . . . . . . . . . . . . 14
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
12.1. Normative References . . . . . . . . . . . . . . . . . . . 14
12.2. Informational References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
VNEF allows service providers to operate multiple services
independently on a common backbone network. To see why this is
required, let us walk through a few example use cases.
1.1. Use Case 1: Operational Independence
Network consolidation is increasingly becoming the norm in service
provider networks. This consolidation creates a common backbone
infrastructure on which the service specific networks provide end-to-
end service-level connectivity. The services include native access
services and packet based services such as Internet and Layer 3 VPNs.
The consolidation provides numerous benefits, including higher
utilization and cost savings in Capital Expenditures (CAPEX) and
Operational Expenditures (OPEX). The model is described in Figure 1.
__________ __________
/ Service1 \ / Service1 \
| Network | | Network |
\----------/ \ / \----------/
\ __________________ /
/ Common backbone \
| Network |
\ /
/ \----------------/ \
__________ / \ __________
/ Service2 \ / Service2 \
| Network | | Network |
\----------/ \----------/
Figure 1: Network Consolidation
In many service providers, the migration of purpose-built service
networks to the common core is a work-in-progress. Additionally, the
common backbone opens up the potential for a new business model,
referred to as "network tenancy". That is, the service provider
instantiates a service dynamically on the common backbone and rents
it out to the customer.
As the number of such services carried on the common backbone
continues to increase, it becomes desirable to create a level of
network and operational isolation, much like what a dedicated network
would have offered. That is, each "service" operator expects to have
an isolated virtual network on the backbone that can be managed
independently. This provides all the classic benefits of
virtualization including efficiency, fast provisioning, and isolation
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while maintaining the advantages of a common backbone network.
1.2. Use Case 2: Network Redundancy
Service providers want the ability to create multiple redundant
networks to protect against failures. Examples of such failures are
severe protocol errors that melt down a majority of the network
elements. Redundancy allows the operator to switch the traffic from
one network to the other. It is worth noting that there have been
attempts at building such redundancy through separate physical
networks in the past, but that turns out to be expensive.
As is clear from the use cases, there are two key aspects to VNEF:
a. An isolated environment on the network elements that can be
operated independently per service ("Element Virtualization")
b. A virtualized network on the core physical network that can be
operated independently per service ("Network Virtualization").
In the following sections, we delve into these aspects of the
framework and draw a set of key properties for each. We recognize
that there are multiple ways to "peel the onion". As such, any
reference to specific terminology describing a solution should be
construed as an example.
1.3. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Terminology
Network Element: A routing and forwarding device in the service
provider network. Other terms used interchangeably for this:
router, platform.
Service: A term used to denote an autonomously administered entity
(an organization, a department, a setup, or an application) that
needs to run an independent network and that has a configured
presence on a network element. Other terms used interchangeably
for this: router slice.
Network slice: a virtual network implemented on the physical
network and assigned to a particular service. How it is
implemented is not really that important. For example, it can be
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constructed using network overlays. What matter are the
properties that it needs to provide, such as traffic isolation,
quality of service. These are discussed in the later sections.
Other terms used interchangeabily for this: virtual network.
Virtual Network Element Framework (VNEF): the architectural
framework discussed in this document.
Service ID: A field used to denote each service running on a
network element. One requirement of the service ID is to organize
the forwarding tables per service and direct packets to the
appropriate forwarding table for processing.
VM: Virtual Machine
3. Problem Statement and Related Areas
Service providers need to consider the following properties of a
common backbone network:
Smooth migration and simple network: Service providers want to
consolidate many service networks into a new common backbone
network without changing network topology and routing / signaling
policy such as IGP, BGP and MPLS.
Network scalability: Routing and signaling protocols need to scale
in proportion to the increase in the number of nodes and protocol
sessions.
Operational policy: Service providers want to keep operational
policy per each service network intact even if we consolidate many
service networks into a new common backbone network.
MTR [RFC4915], [RFC5120], [I-D.ietf-mpls-ldp-multi-topology] allows
service providers to keep network topology and routing / signaling
policy such as IGP, BGP and MPLS intact. However, this technology
does not meet our requirements because 'service' network topologies
may be completely different from the physical topology. Actually, it
depends on the services. Moreover, MTR follows an intrusive design.
That is, it does not provide a true separation of routing and
signaling layers between different services (or a 'service' and the
parent). We refer to this design as the "vertical approach".
Control plane protocols scale higher through hierarchical routing
techniques - multi-area and multi-domain routing. We refer to this
design as the "horizontal approach". These techniques alone do not
meet our requirements because 'service' network topologies might be
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changed from the physical network topology. Furthermore, in this
approach, we can deploy carrier's carrier [RFC4364] to consolidate
the service networks. However, it's realistically difficult to
enable MPLS-capable interfaces on the edge routers in the pure-IP ISP
network. Actually, we need to tranfer MPLS knowledge to operators
and replace or upgrade the exsiting routers to MPLS-capable ones in
the production networks.
4. Reference Model
VNEF's model of operation is depicted in Figure 2.
____________
/ \
__/ Virtualized \___
/ \ Network 1 / \
+---------------+ / \____________/ \ +---------------+
| +-----------+ | / / \__________/\ \ | +-----------+ |
| | Service 1 |---/ / \ \---| Service 1 | |
| +-----------+ | | Backbone | | +-----------+ |
| | | Network | | |
| +-----------+ | \ / | +-----------+ |
| | Service 2 |---\ \ __________ / /----| Service 2 | |
| +-----------+ | \ \/__________\/ / | +-----------+ |
| | \ / \ / | |
+---------------+ \__/ Virtualized \__/ +---------------+
Platform \ Network 2 /
\____________/
Figure 2: Virtualized Networks
A router slice is realized by the allocation of resources on the
network element. Similarly the network slice is realized through a
network overlay-like mechanism across all the elements in the
backbone network. By virtue of separating the resources, the
virtualized network maintains independent control plane, data plane,
and management plane. For example, a route modification by a network
failure on the virtualized network of service 1 in Figure 2 does not
affect the virtualized network of service 2. Therefore, it is easy
to assure different SLAs for service 1 and service 2. After the
implementation of virtualized network, there are many cases that the
virtualized network runs out of allocated resources with the
expansion of service scale. Even in such case, VNEF provides the
adaptive operation to service providers by allocating additional
router resources to the starved virtualized network.
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5. Applications
5.1. Network Wholesale Services
Service providers want to provide a network resource (i.e. a network
slice) to an ISP as shown in Figure 3. In this case, the ISP1 have
own network topology and AS. Also, the ISP1 want to control and
manage their network independently as they used to.
____________
/ \
__/ Virtualized \___
/ \ Network 1 / \
+---------------+ / \____________/ \ +---------------+
| +-----------+ | / / \__________/\ \ | +-----------+ |
| | ISP 1 |---/ / \ \---| ISP 1 |
| +-----------+ | | Backbone | | +-----------+ |
| | | Network | | |
| +-----------+ | \ / | +-----------+ |
| | Service 1 |---\ \ __________ / /----| Service 1 | |
| +-----------+ | \ \/__________\/ / | +-----------+ |
| | \ / \ / | |
+---------------+ \__/ Virtualized \__/ +---------------+
Platform \ Network 2 /
\____________/
Figure 3: Service provider network 1
This service provider have already provided the cloud service
(service1),where they provide some applications to customers on the
cloud network. The ISP1 also can associate with the cloud platform
on the cloud network.
5.2. On-demand Network Services
Some ISPs need a network resource (i.e. a network slice) during the
specific time and period. For instance, this service provider as
shown in Figure 4. provides a network resource to the ISP1
permanently and a network resource to the ISP2 on demand.
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____________
/ \
__/ Virtualized \___
/ \ Network 1 / \
+---------------+ / \____________/ \ +---------------+
| +-----------+ | / / \__________/\ \ | +-----------+ |
| | ISP 1 |---/ / \ \---| ISP 1 |
| +-----------+ | | Backbone | | +-----------+ |
| | | Network | | |
| +-----------+ | \ / | +-----------+ |
| | ISP 2 |---\ \ __________ / /----| ISP 2 | |
| +-----------+ | \ \/__________\/ / | +-----------+ |
| | \ / \ / | |
+---------------+ \__/ Virtualized \__/ +---------------+
Platform \ Network 2 /
\____________/
Figure 4: Service provider network 2
6. Requirement Details
6.1. Dynamic binding - On-demand Service Creation
The solution needs to provide the ability to create a new virtualized
network on demand. The virtualized network should be built
dynamically.
6.2. Control Plane/Routing Layer Separation
The solution needs to support an independent control plane and
routing layer per virtualized network. The conventional routing/
signaling protocols (such as OSPF, IS-IS, BGP, RSVP-TE) should be
able to run on each control plane and routing layer in the
virtualized network.
6.3. Data Plane Separation
The solution needs to have independent forwarding table and data
plane mechanisms per virtualized network. Each data plane on the
virtualized network may be associated with physical interfaces or
logical interfaces (such as VLAN or tunnel).
6.4. Separate Operation of Services
The solution needs to support independent operation of a virtualized
network and service. Administrators should be able to control
routing/ signaling protocols depending on their policy, and manage
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virtualized resources allocated to them (i.e. CPU, Memory, and other
platform resources). Also, the virtualized networks should not
affect each other in any way.
6.5. QoS/SLA
The solution needs to provide an independent QoS/SLA per virtualized
network depending on a service level. Each QoS on the virtualized
network should support eight service levels at least.
6.6. Load Balancing
Each virtualized network may create multiple paths towards a
destination (depending on the control plane algorithms running on the
virtual network). The network elements should support traffic load
balancing, as they would do for a physical network.
6.7. Scale
The solution should scale well with consideration to at least the
following metrics.
1. The number of virtualized networks
2. The number of nodes
3. The number of routes and MPLS LSPs on virtualized networks
7. Architecture
This section defines the VNEF architectural framework and the
associated logical components.
7.1. Element Virtualization
Element virtualization is the mechanism to create an isolated
environment per service on each network element running on the common
backbone. Virtual machine (VM) technology offers a way to implement
element virtualization. Essentially, multiple VMs are created on the
platform by configuration. Each VM represents a service, running its
own operating system, routing protocols, management software, and
other applications. It also satisfies the requirement of independent
software upgradeability per service. Note that VMs are one way of
providing element virtualization. The implementation may choose to
use another container strategy as long as the requirements are
satisfied.
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+---------+ +---------+
|Service_1| |Service_n|
| | ... | |
+---------+ +---------+
+---------------------------+
| Service Manager |
+---------------------------+
Figure 5: Element Virtualization
Figure 5 describes the conceptual model for element virtualization.
"Service Manager" operates as the "owner" software of all resources
in the network element. Its principal role is to arbitrate and
manage the resources of the network element so that multiple service
environments can run in parallel. It responds to operator requests
to create services, assign resources, and associate a set of physical
or logical interfaces with each service. In one particular
implementation choice, the service manager spawns VMs for each
service that is created by the service provider. The creation of
virtual networks per service is described in the next section. For
example, for network overlay model of building virtual networks, the
service manager software acts as the server conduit that listens to
requests from the service's software.
The "service manager" also guarantees performance isolation between
services. If VMs are utilized to implement element virtualization,
there are well-known resource allocation mechanisms to allocate CPU
and memory per VM. This needs to be configuration- driven so that
the operator can deploy customized policies for resource allocation
(e.g. proportional sharing or priviledged allocation for certain
services).
7.2. Network Virtualization
Network virtualization is the mechanism to create independent virtual
networks over the same physical network infrastructure. The primary
characteristics of virtual networks are:
o Each virtual network can be engineered and managed separately (by
the operator of the corresponding service). As an example, all
routing protocols should be able to run on each virtual network to
create the desired logical topology.
o Isolation of one service's traffic from other services.
Virtual network constructs are not new (e.g.
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[I-D.ietf-nvo3-overlay-problem-statement] describes a few of the
constructs). We focus on network overlays to create virtual networks
in this document. More specifically, we will discuss a specific
technology of a network overlay design using MPLS LSPs: GMPLS UNI
([RFC4208]). The LSPs can either be created inline on the network
element or as a separate layer ([RFC5440],
[I-D.crabbe-pce-stateful-pce]).
GMPLS UNI calls for a clean separation between the edge nodes and
core nodes. We find that suitable in the context of the interface
between a service and the core network. The reference model from
[RFC4208] is reproduced here.
Overlay Overlay
Network +----------------------------------+ Network
+---------+ | | +---------+
| +----+ | | +-----+ +-----+ +-----+ | | +----+ |
| | | | | | | | | | | | | | | |
| -+ EN +-+-----+--+ CN +----+ CN +----+ CN +---+-----+-+ EN +- |
| | | | +--+--| | | | | | | | | | |
| +----+ | | | +--+--+ +--+--+ +--+--+ | | +----+ |
| | | | | | | | | |
+---------+ | | | | | | +---------+
| | | | | |
+---------+ | | | | | | +---------+
| | | | +--+--+ | +--+--+ | | |
| +----+ | | | | | +-------+ | | | +----+ |
| | +-+--+ | | CN +---------------+ CN | | | | | |
| -+ EN +-+-----+--+ | | +---+-----+-+ EN +- |
| | | | | +-----+ +-----+ | | | | |
| +----+ | | | | +----+ |
| | +----------------------------------+ | |
+---------+ Core Network +---------+
Overlay Overlay
Network Network
Legend: EN - Edge or Service Node
CN - Core Node
Figure 6: Overlay Network
The core network depicted as the large box in the center is the
representation of the physical network. The nodes marked as 'EN' and
described as "Overlay Network" represent a single virtual network for
a particular service. In essence, the 'EN' nodes belong to a service
(hosted by a virtualized network element as described in
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Section 7.1). They request links to be established between them to
the 'CN' nodes. The links come up as GMPLS LSPs using the overlay
signaling mechanism. Collectively, the links between all the 'EN'
nodes belonging to a service represent the topology of that service.
The links show up as normal interfaces to the 'EN' nodes. The 'EN'
nodes can, thus, run normal routing protocols on the top to engineer
the desired traffic forwarding paths.
7.3. Service Identification
When the network element receives a packet from the edge, how does it
choose which service the packet belongs to? There are a couple of
design choices:
1. The edge-facing interfaces are associated with particular
services by configuration. This could be the entire physical
interface or divided into multiple sub-interfaces (e.g. VLANs)
per service.
2. A per-service policy is configured to look at the packet
attributes and dynamically identify a service.
Similarly, when a packet is received from the core, the service is
identified based on the virtual network that carried the packet. For
example, if GMPLS UNI LSPs are used as the virtual network construct,
the top MPLS label identifies the LSP and hence the service.
8. Comparison with Other Technologies
8.1. VRF
Most of the routers today support the concept of a virtual routing
and forwarding (VRF) [RFC4364]. Though there are separate forwarding
tables maintained per VRF, the technology fails to meet the
requirements discussed in this document as follows:
There is no operational isolation between different VRFs on a
network element
There is no network isolation (both for control plane and
forwarding plane) on the core network between VRFs.
8.2. Network Virtualization Over L3
[I-D.ietf-nvo3-overlay-problem-statement] describes an architectural
requirement for virtualizing the network. However, it focuses
primarily on data center and multi- tenancy and the requirements do
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not apply to service provider networks.
9. Acknowledgments
The authors wish to thank Tony Li, Akash Deshpande, Rex Fernando, and
John Bettink for all the discussions that led to the architectural
model described in the document.
10. IANA Considerations
11. Security Considerations
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
12.2. Informational References
[I-D.crabbe-pce-stateful-pce]
Medved, J., Minei, I., Crabbe, E., and R. Varga, "PCEP
Extensions for Stateful PCE",
draft-crabbe-pce-stateful-pce-02 (work in progress),
January 2012.
[I-D.ietf-mpls-ldp-multi-topology]
Zhao, Q., Fang, L., Zhou, C., Li, L., and K. Raza, "LDP
Extensions for Multi Topology Routing",
draft-ietf-mpls-ldp-multi-topology-09 (work in progress),
October 2013.
[I-D.ietf-nvo3-overlay-problem-statement]
Narten, T., Gray, E., Black, D., Fang, L., Kreeger, L.,
and M. Napierala, "Problem Statement: Overlays for Network
Virtualization",
draft-ietf-nvo3-overlay-problem-statement-04 (work in
progress), July 2013.
[RFC3746] Yang, L., Dantu, R., Anderson, T., and R. Gopal,
"Forwarding and Control Element Separation (ForCES)
Framework", RFC 3746, April 2004.
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[RFC4110] Callon, R. and M. Suzuki, "A Framework for Layer 3
Provider-Provisioned Virtual Private Networks (PPVPNs)",
RFC 4110, July 2005.
[RFC4208] Swallow, G., Drake, J., Ishimatsu, H., and Y. Rekhter,
"Generalized Multiprotocol Label Switching (GMPLS) User-
Network Interface (UNI): Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Support for the Overlay
Model", RFC 4208, October 2005.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, June 2007.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120, February 2008.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element
(PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
Authors' Addresses
Kenji Kumaki
KDDI Corporation
Garden Air Tower
Iidabashi, Chiyoda-ku, Tokyo, 102-8460
Japan
Email: ke-kumaki@kddi.com
Pradosh Mohapatra
Cumulus Networks
Email: pmohapat@cumulusnetworks.com
David Meyer
Brocade
Email: dmm@1-4-5.net
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Kannan Varadhan
Cisco Systems
Email: kvaradha@cisco.com
Zafar Ali
Cisco Systems
Email: zali@cisco.com
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