Internet DRAFT - draft-huang-sfc-use-case-recursive-service
draft-huang-sfc-use-case-recursive-service
Service Function Chaining C. Huang
Internet Draft Carleton University
Intended status: Informational Jiafeng Zhu
Expires: July 13, 2015 Huawei
Peng He
Ciena
January 13, 2015
SFC Use Cases on Recursive Services
draft-huang-sfc-use-case-recursive-service-01.txt
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Abstract
Service function chaining (SFC) provides various services that can
be tailored to different requirements from diversified user groups,
where each user group forms a collective client that requires
similar service. SFC is typically deployed as a service overlay with
its own service topology on top of existing network topology. This
kind of virtualized structure naturally enables recursive service
relationship where a client may become a service provider and resell
SFC services to its own user groups. Alternatively, a client may
also choose to ask its service provider to provide a structured
service for its user groups. This document describes some exemplary
use cases that show the usage of recursive (e.g. nested) or
structured service function chaining relationship.
Table of Contents
1. Introduction ................................................ 2
2. Conventions used in this document ........................... 3
3. Use Case .................................................... 3
4. Analysis .................................................... 6
5. IANA Considerations ......................................... 6
6. Refernces ................................................... 8
1. Introduction
New services such as service function chaining (SFC) are becoming
popular with network function virtualization. Traditionally a
service chain consists of a set of dedicated network service boxes
such as firewall, load balancers, and application delivery
controllers that are concatenated together to support a specific
application. With a new service request, new devices must be
installed and interconnected in certain order. This can be a very
complex, time-consuming, and error-prone process, requiring careful
planning of topology changes and network outages and incurring high
OPEX. This situation is exacerbated when a tenant requires different
service sequences for different traffic flows or when multiple
tenants share the same underlying network.
Today's SFC takes a new approach built upon network function
virtualization (NFV). It involves the implementation of network
functions in software that can run on a range of industry standard
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high volume servers, switches, and storage. Through NFV, service
providers can dynamically create a virtual environment for a
specific service chain and eliminate the dedicated hardware and
complex labor work for supporting a new service function chain
request.
One of the great potentials NFV can enable is the capability to
support recursive SFC service. A client of SFC service can resell
customized SFC services to its own user groups, where the client
becomes a service provider and its subscribed user groups become new
clients, without adding any dedicated hardware. This kind of
recursive (or nested) service relationship is quite common in daily
life. Big wholesalers can sell products to smaller wholesalers and
the smaller wholesalers then sell those products to other small
wholesalers or directly to end users. In telecom area, the Carriers'
Carriers concept is defined in RFC 4364[1], which comes from similar
idea. Forming recursive business relationship has been proven to be
a successful business model due to the flexibility and efficiency it
provides. The same arguments can also be applied to SFC service
providers.
A distinguished characteristic of recursive SFC service is that the
service provider at each level can have its own administrative
authority built over the virtual environment provided by the lower
level, leading to a hierarchy of administrative levels. This kind of
hierarchical structure poses both opportunities and challenges for
service providers.
While a service provider at each level can have its own
administrative authority, it can also choose to delegate its
authority to its service provider. In the simple case, all levels of
services will be delegated to one service provider, which will in
turn provide a structured service [2].
In a later section, a use case will be presented to illustrate a
specific application scenario.
2. Conventions used in this document
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.
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
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3. Use Case
There are numerous use cases that recursive SFC service can be
applied to. A typical use case is described below.
Consider a scenario where Enterprise B outsources its enterprise
network to a datacenter operated by a cloud service provider A. This
type of scenario has been widely considered as one of the major
applications of cloud computing. It is believed that enterprises can
save their costs and improve their IT services by exploring the
elasticity and dynamic sharing nature of a datacenter environment.
Different enterprises typically have different requirements about
their outsourced enterprise networks in terms of topology and
service function.
Consider the case that Enterprise B requests its outsourced network
to have mesh topology with each node dedicated to a special service
function. After receiving the request from Enterprise B, Cloud
Provider A will create all requested virtual service function nodes
with a mesh topology out of its infrastructure. Provider A will also
need to assign an ID which is unique in his authority to identify
this mesh service function chain.
+-----+
+---+Video|
+---+ +---+ +---+ | +-----+
+---+SSL+--+--+DPI+--+--+ADC+---+
| +---+ | +---+ | +---+ | +---+
| +---------+ +---+Web|
| +---+
|
+-+-+ +---+ +--+ +---+
---+NAT+---+WOC+---+LB+---+Web|
+-+-+ +---+ +--+ +---+
|
|
| +---+ +---+ +--+ +---+
+-----+SSL+---+WOC+---+LB+---+Web|
+---+ +---+ +--+ +---+
Figure 1 : Service function chains created by Enterprise B.
Suppose initially Enterprise B wants to support two user groups. One
group includes all its employees. The other group is for visitors
only. The two user groups have distinctive service function
requirements. Therefore Enterprise B has to create two SFCs out of
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its outsourced enterprise network. The first service chain, designed
for its employees, will force traffic flows to go through NAT
(Network Address Translation), SSL (Secure Socket layer)/TLS
(Transport Layer Security), DPI (Deep Packet Inspection) if
necessary, ADC (Application Delivery Controller), and various
servers as shown in Fig.1. In this SFC, NAT, TLS, and DPI provide
strong firewall service while ADC conducts service routing and load
balance. The second SFC, designed for guest visitors, will go
through NAT, WOC (Web Optimization Control), LB (Load Balancer), and
web servers as shown in Fig.1. Here NAT provides limited firewall
function with access control. WOC and LB are designed to optimize
server efficiency. Enterprise B will create these two service chains
as overlays over its outsourced enterprise network. Because the
underlying service chain has a mesh topology with all different
service function nodes, Enterprise B can create the two service
chains very fast with minimal efforts.
Suppose Enterprise B later wants to add another user group for one
of its customers, called Customer C, it can do so easily by adding
another service chain which may include NAT, SSL/TLS, WOC, and LB as
shown in Fig.1. Each user group is a tenant for Enterprise B.
Therefore Enterprise B needs to assign an ID for each tenant so that
it can differentiate traffic streams for the three different
tenants. Each Id needs to be unique for Enterprise B. Customer C may
be an enterprise that has many departments who want to access the
resources available at Enterprise B's network. Customer C is given
full control of the service chain created for it. Customer C may
then create a service chain and an ID for each department that needs
access.
+---+ +--+ +---+
|SSL+-----------+LB+---+Web| SFC created by
+---+ +--+ +---+ Client C
: : :
: : :
+---+ +---+ +---+ +--+ +---+
|NAT+---+SSL+---+WOC+---+LB+---+Web| SFC created by
+---+ +---+ +---+ +--+ +---+ Enterprise B
: : : : :
: : : : :
+---+ +---+ +---+ +---+ +--+ +---+
|DPI| |NAT| |SSL| |WOC| |LB| |Web| SFC created by Cloud
+---+ +---+ +---+ +---+ +--+ +---+ Provider A
| | | | | |
+--------+-------+-------+------+-------+
Figure 2 : Recursive service function chain structure.
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The above structure clearly leads to a recursive service
relationship as shown in Fig.2 where dot lines show mapping
relationship and dash lines are service chains (For clearness, only
one service chain is shown for each level.). Cloud Provider A
provides the first level SFC that includes a customized topology and
generic service function nodes. Enterprise B provides the second
level SFC which includes three customized SFCs. Customer C builds
the third level SFCs for several departments over the SFC created by
Enterprise B. As we mentioned before, this structure bears some
similarity to the Carriers' Carriers concept defined in RFC 4364[1].
4. Analysis
One of the key issues introduced by the hierarchy of recursive SFC
relationship is the relationship between different levels. There are
three types of relationship that can be envisioned. The first one is
called independent relationship where the lower level is agnostic of
the SFCs created by upper levels. Therefore all the service
functions created by an upper level will be implemented and enforced
at the upper level SFC modules while the lower level modules are
completely unaware. When traffic arrives at a lower level module,
the module processes the incoming traffic based on its service
function requirements and de-multiplexes the traffic to the right
upper level module using the IDs it assigned. The lower level module
does not execute the service functions of upper level. The upper
level applies different service functions based on the IDs it
assigned. In this case, the upper level module does not have to be
the same type as the lower level module. Hence there could be a new
requirement for SFP header encapsulation, e.g., SFC header
'stacking', similar to MPLS label stacking or even Ethernet VLAN tag
stacking. A simple example is encryption/decryption service. The
lower level SFC contains the encryption/decryption service to
encrypt/decrypt the packet contents after the SFC header, the upper
level SFC(s) has to properly deal with the SFC header received from
the lower level, e.g., SFC header stacking might be worthy of
consideration.
The other type is opaque relationship where service functions
defined by upper level may require collaboration from lower level.
For example, Enterprise B may inform Cloud Provider A about some
service functions it needs and ask Cloud Provider A to help
implement those service functions. When traffic arrives at Cloud
Provider A, it will identify traffic flows using both the ID it
assigned and the ID assigned by upper level as a concatenated ID and
then apply associated service functions. The traffic stream will not
be delivered to upper level for those requested service functions.
In this case, upper level functions inherit properties from lower
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level functions. They are also constrained by the functions
available from lower level. However the upper level can create new
properties such as new firewall rules as long as it doesn't violate
the constraint posed by the lower level. Whenever service functions
at lower level are changed, upper level service functions will also
be changed. However changes made to the upper level may not apply to
lower level. Fig.2 is an example of the opaque relationship.
In both cases, the upper level and lower level represent different
authorities. Cloud Provider A decides the mesh service chain while
Enterprise B decides the three linear service chains for its three
tenants. In reality, a tenant is more likely to retain some
functions as transparent (e.g. encryption function) and some
functions as opaque (e.g. LB).
Other than the two types mentioned above, it is also possible that
the Enterprise C delegates its administrative role to Enterprise B,
which in turn delegates its authority to Cloud Provider A. The
benefit of this single administrative domain approach is that
Enterprises B and C do not need to handle the administrative work.
However, both B and C need to disclose all information to A, forming
a transparent relationship. With transparent relationship, Cloud
Provider A has to implement all SFCs with a hierarchical structure
that satisfies the roles and responsibilities distributed according
to the organizational structure of Enterprises B and C [2]. This
kind of structured service is likely to become one of the SFC
deployment paradigms.
The above discussions show some special properties unique to
recursive service chain. It is necessary to investigate how these
properties can be supported using existing protocols, proposed SFC
mechanisms, various other mechanisms, or even new proposals.
5. IANA Considerations
It is recommended that IANA assign a port in UDP and another port
number in TCP to identify the existing of SFLs in Layer 5. The top
level SFL of a SFL stack can use all existing port number
assignments to identify various applications.
6. References
[1] E. Rosen and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks
(VPNs)," IETF RFC 4364, February, 2006.
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[2] R. Szabo, A. Csazzar, K. Pentikousis, M. Kind, and D. Daino,
"Unifying Carrier and Cloud Networks: Problem Sttatement and
Challenge," IETF draft, Oct. 2014.
< https://tools.ietf.org/html/draft-unify-nfvrg-challenges-00>
Authors' Addresses
Changcheng Huang
Department of Systems and Computer Engineering
Carleton University
1125 Colonel By Drive
Ottawa, ON K1S 5B6
Canada
Email: huang@sce.carleton.ca
Jiafeng Zhu
Huawei Technologies Inc
Santa Clara, CA
US
Email: Jiafeng.zhu@huawei.com
Peng He
Ciena Corp
Email: phe@ciena.com
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