Service Function Chaining C. Huang
Internet Draft Carleton University
Intended status: Informational Jiafeng Zhu
Expires: January 1, 2015 Huawei
Peng He
Ciena
July 1, 2014
SFC Use Cases on Recursive Service Function Chaining
draft-huang-sfc-use-case-recursive-service-00.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. This document describes some
exemplary use cases that show the usage of recursive (e.g. nested)
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......................................................7
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
high volume servers, switches, and storage. Through NFV, service
providers can dynamically create a virtual environment for a
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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 each
level of service provider has 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. 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.
3. Use Case
There are numerous use cases that recursive SFL 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
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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.
The two user groups have distinctive service function requirements.
Therefore Enterprise B has to create two SFCs out of 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 the 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
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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+---+WOC+----------+Web| SFC created by
+---+ +---+ +---+ Client C
: : :
: : :
+---+ +---+ +---+ +--+ +---+
|NAT+---+SSL+---+WOC+---+LB+---+Web| SFC created by
+---+ +---+ +---+ +--+ +---+ Enterprise B
: : : : :
: : : : :
+---+ +---+ +---+ +--+ +---+
|NAT| |SSL| |WOC| |LB| |Web| SFC created by Cloud
+---+ +---+ +---+ +--+ +---+ Provider A
| | | | |
+-------+-------+------+-------+
Figure 2 : Recursive service function chain structure.
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
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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
two types of relationship that can be envisioned. The first one is
called opaque 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 ID 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 (e.g. the lower level may be a NAT
function while the upper level may be SSL function). But the upper
level module will be based on the output of lower level module. For
example, traffic that has been filtered by lower level cannot be
recovered by upper level. This is why it is called opaque.
The other type is transparent relationship where service functions
defined by upper level may require collaboration from lower level.
For example, Enterprise B may inform Cloud Provider A about the SFCs
it has created and ask Cloud Provider A to help implement flows
belonging to different SFCs. 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 de-
multiplexed to upper level. In this case, upper level functions
inherit properties from lower 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
transparent relationship.
In both cases, the upper level and lower level represent different
authorities. Cloud Provider A decides the mesh service chain while
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Enterprise B decides the three linear service chains for its three
tenants. This is key feature of recursive service function chaining.
In practice, a tenant is more likely to retain some functions as
opaque (e.g. encryption function) and some functions as transparent
(e.g. LB).
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.
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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