Service Function Chaining S. Homma
Internet-Draft K. Naito
Intended status: Informational NTT
Expires: August 1, 2016 D. R. Lopez
Telefonica I+D
M. Stiemerling
NEC/H-DA
D. Dolson
Sandvine
A. Gorbunov
Nokia
N. Leymann
Deutsche Telekom AG
P. Bottorff
D. Fedyk
HP Enterprise
January 29, 2016
Analysis on Forwarding Methods for Service Chaining
draft-homma-sfc-forwarding-methods-analysis-05
Abstract
This document presents the results of analyzing packet forwarding
methods and path selection patterns for achieving Service Chaining.
In Service Chaining, data packets need to be forwarded to the
appropriate service functions deployed in networks based on service
provided for the packets, and distribution of the service-oriented
route information and steering data packets following the route
information would be required.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 1, 2016.
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Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 4
3. Classification of Forwarding Methods and SP Selection
Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Forwarding Methods . . . . . . . . . . . . . . . . . . . 5
3.1.1. Method 1: Forwarding Based on Flow Identifiable
Information . . . . . . . . . . . . . . . . . . . . . 6
3.1.2. Method 2: Forwarding with Stacked Headers . . . . . . 7
3.1.3. Method 3: Forwarding Based on Service Chain
Identifiers . . . . . . . . . . . . . . . . . . . . . 9
3.2. Service Path Selection Patterns . . . . . . . . . . . . . 12
3.2.1. Pattern 1: Static Selection of End-to-End Service
Path . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2.2. Pattern 2: Dynamic Selection of Segmented Service
Path . . . . . . . . . . . . . . . . . . . . . . . . 16
4. Consideration on Forwarding Methods and Paths Selection
Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.1. Analysis of Forwarding Methods . . . . . . . . . . . . . 22
4.1.1. Analysis of Method 1: Using Flow Identifiable
Information . . . . . . . . . . . . . . . . . . . . . 22
4.1.2. Analysis of Method 2: Stacking Headers . . . . . . . 23
4.1.3. Analysis of Method 3: Using Service Chain Identifier 24
4.2. Analysis of Service Path Selection Patterns . . . . . . . 27
4.2.1. Analysis of Pattern 1: Static SP Selection . . . . . 27
4.2.2. Analysis of Pattern 2: Dynamic SP Selection . . . . . 28
4.3. Example of selecting Methods and Patterns . . . . . . . . 32
4.3.1. Example#1: Enterprise Datacenter Network . . . . . . 32
4.3.2. Example#2: Current Mobile Service Providers Network . 32
4.3.3. Example#3: Fixed and Mobile Converged Service
Providers Network . . . . . . . . . . . . . . . . . . 34
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 35
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6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 35
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37
1. Introduction
Some IETF working groups of and other Standards Developing
Organizations are now discussing use cases of a technology that
provides service-oriented traffic forwarding schemes to convey
packets to the various service functions, deployed in networks, for
providing network services. In this document, we define such
technology as Service Chaining. (This draft does not focus only on
"Service Function Chaining (SFC)" architecture, and thus, use the
term "Service Chaining." SFC is one of approaches to realize Service
Chaining.) There are several methods to achieve Service Chaining,
and the applicable method will vary depending on the service
requirements of individual networks.
This draft assumes that Service Chaining is achieved by the following
steps:
a. A traffic classification function identifies the service that is
associated to each incoming packets by inspecting the key
information such as IP address or 5-tuple.
b. The forwarding path used by packets for reaching the appropriate
service functions, is established according to the services
provided for the packets. The path might be established in
advance.
c. Forwarding functions forward the packets to the next destination
along the path established in step b.
d. A service function operates on received packets. Once the
invocation of a service function is completed, the packet is
forwarded to the next forwarding function.
e. Steps c and d are repeated until each packet has been transferred
to all required service functions.
f. After a packet has been transferred to all required Service
Functions, it is forwarded to its original destination.
There are several forwarding methods for Service Chaining, and they
can be classified into certain categories in terms of distribution of
information for setting the paths and decision of the paths. The
methods used to distribute the information for path setting and the
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patterns used to decide the paths will affect the mechanism of
Service Chaining in terms of scalability and service flexibility.
The applicable methods vary depending on network requirements, and
thus, classifying and determining forwarding methods will be
important in designing the architecture of Service Function Chaining
(SFC). This document provides the results of analysis of different
forwarding methods for Service Chaining.
OAM, security, and redundancy are outside the scope of this draft.
2. Definition of Terms
Term "Classification", "Classifier" referred to [RFC7665]. Term
"Service Function", "Service Node" referred to
[I-D.ietf-sfc-dc-use-cases].
Service Chaining: A technology that enables data packets to invoke a
set of service functions.
Classification: Locally instantiated matching of traffic flows
against policy for subsequent application of the required set of
network service functions. The policy may be customer/network/
service specific.
Classifier (CF): An element that performs classification.
Service Function (SF): A function that is responsible for specific
treatment of received packets. A Service Function can act at
various layers of a protocol stack (e.g. at the network layer or
other OSI layers). A Service Function can be a virtual element or
be embedded in a physical network element. One of multiple
Service Functions can be embedded in the same network element.
Multiple occurrences of the Service Function can be enabled in the
same administrative domain.
One or more Service Functions can be involved in the delivery of
added-value services. A non-exhaustive list of Service Functions
includes: firewalls. WAN and application acceleration, Deep
Packet Inspection (DPI), LI (Lawful Intercept) module, server load
balancers, NAT44 [RFC3022], NAT64 [RFC6146], NPTv6 [RFC6296],
HOST_ID injection, HTTP Header Enrichment functions, TCP
optimizer, etc.
Forwarder (FWD): The entity, responsible for forwarding data packets
according to the ordered set of service functions that need to be
invoked. A forwarder maintains one or more forwarding tables,
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which contain entries that asset the forwarder in its forwarding
decision-making process.
Control Entity (CE): One or a set of control entities responsible
for managing service topology and indicating forwarding
configurations to forwarders.
Service Chain (SC): A service chain defines an ordered list of
service functions that must be applied to packets selected as a
result of classification. The implied order may not be a linear
progression as the architecture allows for nodes that copy to more
than one branch.
Service Path (SP): The forwarding path followed by packets that are
associated to a given service chain. Packets follow a service
path through the requisite service functions that need to be
invoked, as per the service chain instructions. Service path
shows a specific path that traverses several service function
instances. For example, SC is written as SF#1 -> SF#2 -> SF#3
(This shows an ordered list of SFs), and SP is written as
SF#1_1(1_1 means instance 1 of SF1) -> SF#2_1 -> SF#3_1.
Segmented Service Path: A Segmented Service Path is an actual path
established between FWDs. A service path might be composed of
some segmented service paths.
Service Chaining Domain (SC Domain): The domain managed by one or a
set of CEs.
Service Path Information (SP Information): The information used to
forward packets to the appropriate SFs according to the service
that needs to be provided. Examples of SP information include
routing configuration for forwarders, headers for forwarding
packets to required SFs, and service/flow identifiable tags.
3. Classification of Forwarding Methods and SP Selection Patterns
3.1. Forwarding Methods
In Service Chaining, data packets are transferred to service
functions, which might be located outside the regular computed path
to the original destination. Therefore, a routing mechanism that is
different from general L2/L3 switching/forwarding might be required.
The forwarding mechanism can be classified into three methods in
terms of distribution of SP information and packet forwarding.
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3.1.1. Method 1: Forwarding Based on Flow Identifiable Information
The mechanism of method 1 is shown in Figure 1. In this method,
forwarding configuration information is based on flow identifiable
information, such as 5-tuple (e.g. dst IP, src IP, dst port, src
port, tcp) are indicated to the CF and each FWD. There might be an
CE to handle this. The flow identifiable information can be
constructed with some fields of L2, L3 or L4 or combination thereof.
The information can be configured either before packets arrive, or at
the time packets arrive at CF and FWD. Each FWD identifies the
packets with flow identifiable information and forwards the packets
to the SFs according to the configuration. This method does not
require the modification of any field in the original packet header.
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*Distribution model of SP information*
+----------------+
| Control Entity |
+----------------+
^ | indication of routing configuration
| | based on packet identifiable information
| +---------------+-------------------------------+--------->
| | | |
| | | |
| v v v
+--------+ +-------+ +------+ +-------+
------>| CF |------> | FWD |------> | SF#1 |------>| FWD |----->
+--------+ +-------+ +------+ +-------+
////////////////////////////////////////////////////////////////////////
*Forwarding Tables*
Locate: [CF] [FWD] [FWD]
Table: 192.168.1.1 192.168.1.1 192.168.1.1
->FWD#1 ->SF#1 ->SF#2
10.0.1.1 10.0.1.1 10.0.1.1
->FWD#1 ->FWD#2 ->SF#2
... ... ...
////////////////////////////////////////////////////////////////////////
*Condition of Packet*
Locate: [CF] [FWD] [SF#1] [FWD]
+-------+ +-------+ +-------+ +-------+
Packet: | PDU | | PDU | | PDU | | PDU |
+-------+ +-------+ +-------+ +-------+
Figure 1: Forwarding Based on Flow Identifiable Information
3.1.2. Method 2: Forwarding with Stacked Headers
The mechanism of method 2 is shown in Figure 2. In this method, the
CF classifies packets and stacks headers in which actual network
address is included, e.g., MPLS, GRE headers or IPv6 Segment Routes,
onto the packets based on the classification. The packet is
transferred to the destination according to the outermost header, and
a SF or FWD, as the destination, removes the outermost header after
receiving the packet. The processes are repeated until all stacked
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headers are removed. This method does not require any forwarding
entries for forwarding packets based on the service information.
*Distribution model of SP information*
+----------------+
| Control Entity |
+----------------+
^ |
| | indication of
| | stacking headers
| v
+--------+ +-------+ +------+ +------+
-------->| CF |------>| SF#1 |------>| SF#2 |------>| SF#3 |------>
+--------+ +-------+ +------+ +------+
////////////////////////////////////////////////////////////////////////
*Forwarding Tables*
Locate: [CF]
Table: 192.168.1.1 __/__/__/__/__/__/__/__/__/__/__/__/__/
->Stack #1,2,3 __/ Packets are forwarded to SFs by __/
10.0.1.1 __/ the outermost header. __/
->Stack #1,3 __/__/__/__/__/__/__/__/__/__/__/__/__/
...
////////////////////////////////////////////////////////////////////////
*Condition of Packet*
Locate: [CF] [SF#1] [SF#2] [SF#3]
+--------+
Header: |To SF#1 |
+--------+ +--------+
|To SF#2 | |To SF#2 |
+--------+ +--------+ +--------+
|To SF#3 | |To SF#3 | |To SF#3 |
+--------+ +--------+ +--------+
: : : :
+--------+ +--------+ +--------+ +--------+
Packet: | PDU | | PDU | | PDU | | PDU |
+--------+ +--------+ +--------+ +--------+
Figure 2: Forwarding with Stacked Multiple Headers
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3.1.3. Method 3: Forwarding Based on Service Chain Identifiers
The mechanism of this method is shown in Figure 3. In this method,
the corresponding service chain identifier is mapped to each packet
by a CF based on the classification. The forwarding configuration
based on the identifiers is sent to each FWD. Each FWD identifies
the SP assigned to the received packet from the identifier, and
forwards the packet to the next hop. After a packet has traversed
all SFs, the identifier is removed and the packet is transported to
the original destination.
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*Distribution model of SP information*
+----------------+
| Control Entity |
+----------------+
^ | indication of attached tag
| | and routing configuration based on tags
| +----------------+------------------------------+--------->
| | | |
| | | |
| v v v
+--------+ +-------+ +------+ +-------+
----->| CF |------> | FWD |------>| SF#1 |------>| FWD |----->
+--------+ +-------+ +------+ +-------+
//////////////////////////////////////////////////////////////////////
*Forwarding Tables*
Locate: [CF] [FWD] [FWD]
Table: 192.168.1.1 IF ID#1,3 IF ID#1,2,5
->Stack ID#1 ->SF#1 ->SF#2
10.0.1.1
->Stack ID#2
... ... ...
//////////////////////////////////////////////////////////////////////
*Condition of Packet*
Locate: [CF] [FWD] [SF#1] [FWD]
+-------+ +-------+ +-------+ +-------+
SC-ID: | ID#1 | | ID#1 | | ID#1 | | ID#1 |
+-------+ +-------+ +-------+ +-------+
Packet:| PDU | | PDU | | PDU | | PDU |
+-------+ +-------+ +-------+ +-------+
Figure 3: Forwarding Based on Service Chain Identifiers
Then, there are mainly three approaches to map service chain
identifiers to packets as follows.
o Tagging an extra header:
In this approach, an extra header which has a service chain
identifier is attached on each packet. This document defines such
headers as service identifiable tags. Some existing tags, such as
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VLAN-tag or MPLS-tag, or dedicated headers, such as NSH, could be
used as service identifiable tags. As an example, SFC[RFC7665] is
categorized into this approach. An example of packet format in
tagging approach with NSH is shown in Figure 4. In this example,
a service chain identifier is included in NSH.
+----------+-------+--------+-------------~~--+
| NSH | Ether | IPv6 |IPv6 Payload |
| \SC-ID | Header| Header | |
+----------+-------+--------+-------------~~--+
|--- Ethernet Packet ---|
Figure 4: Packet Format in Tagging Approach
o Inserting into an optional field:
In this approach, a service chain identifier is inserted into an
optional field inside a packet frame, such as IPv6 extension
header. An example of an IPv6 packet with a service chain
identifier inserted as an extension header is shown in Figure 5.
+-------+--------+----------+-------------~~--+
| Ether |IPv6 |IP Opt.Fld|IPv6 Payload |
| Header|Base Hdr| \SC-ID | |
+-------+--------+----------+-------------~~--+
|-- IPv6 Header --|
|--- Ethernet Packet ---|
Figure 5: Packet Format in Inserting Approach
o Overloading on a destination or source address:
In this approach, service chain identifier is overloaded on a
destination or a source address such as MAC or IP address. In
other words, the addresses are used for both showing the
destination or source in network and identifying service chain
which each packet belongs to. An address is required for each hop
in a service chain, and FWDs switch the address to new one for the
next hop by referring the address of the received packet. An
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example of using destination address overloading is shown in
Figure 6. In this example, SFs are used as L2 transparent mode,
and service chain identifiers are overloaded on destination MAC
addresses. FWD2 refers the destination MAC address which shows
the address for Port B, and changes it to the address for port D
for sending the packet to the next hop in the service chain. When
using non-transparent SFs in the overloading approach, the
identifier is carried from the FWD to the SF in the source
address(SA) and is carried from the SF to the FWD in the
destination address(DA). More detailed processes of the
overloading approach using MAC addresses is described in Ethernet
MAC Chaining[I-D.fedyk-sfc-mac-chain].
*Network Structure*
Port A Port B Port C Port D
| | | |
| | | |
.------. | +[SF1]+ | .------. | +[SF2]+ | .------.
/ \v | | v/ \v | | v/ \
--# FWD1 #--+ +--# FWD2 #--+ +--# FWD3 #--
\ / ^ \ / ^ \ /
'------' | '------' | '------'
| |
. . . . . . . . | . . . . . . . . . . .| . . . . . . . . . . . . .
| |
*Packet Frame* | |
| |
+--------+-------~-+ +--------+-------~-+
|MAC-DA:B| Payload | |MAC-DA:D| Payload |
+--------+-------~-+ +--------+-------~-+
============== Flow Direction ==============>
Figure 6: Overview of DA Overloading Approach
3.2. Service Path Selection Patterns
Since SC contains only logical information (e.g., a set of services
that are associated with flows and their sequences), the actual
instances, which are called SPs, are needed in order for the
forwarding process to work. In this process, an instance of SP is
created at certain points during a packet's delivery. Therefore, to
forward packets, the SC needs to be turned into an SP, which
indicates specific FWDs (or switches, routers) and SFs that the
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packets will be forwarded to. From the perspective of points
translating SC to SP, the methods that establish SPs from end-to-end
are classified into two patterns.
3.2.1. Pattern 1: Static Selection of End-to-End Service Path
The translation point is a CF; that is, the SP is statically pre-
established as an end-to-end path and a CF forwards packets along the
appropriate path based on the result of the classification. Each FWD
on the SP has a forwarding table to uniquely determine the next
destination of packets, and each FWD statically forwards the received
packets toward the next destination based on the table. FWD requires
only a function to receive indications of forwarding configurations
from the CE. Pattern 1 can be achieved in the following models.
3.2.1.1. SF Dedicated Model: Network Slicing Model
In this model, an SF instance (or a set of SF instances) is used by
only one single SP; in other words, a set of SF instances is prepared
for each SP. This model also enables operators to establish SPs
without any FWDs by slicing network physically or virtually and
deploying a set of SFs required for service providing in each sliced
network. A CF assigns packets to the network in which the
appropriate SF set is installed inline, and the packets traverse the
SFs by being forwarded along the pre-configured route. The overview
of network slicing model is shown in Figure 7.
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*Path Structure*
* * * * * * * * * * * * * * * * * * * * * * *
* network#1 *
+----+ * +------+ +------+ +------+ *
| |SC#1 * | SF#1 | | SF#2 | | SF#3 | * SP#1
| |=======================================================>
| | * +------+ +------+ +------+ *
| | * * * * * * * * * * * * * * * * * * * * * * *
| |
| | * * * * * * * * * * * * * * * * * * * * * * *
| | * network#2 *
| | * +------+ +------+ *
| |SC#2 * | SF#4 | | SF#5 | * SP#2
| |=======================================================>
->| CF | * +------+ +------+ *
| | * * * * * * * * * * * * * * * * * * * * * * *
. .
. .
. .
* * * * * * * * * * * * * * * * * * * * * * *
* network#n *
* +------+ +------+ +------+ *
| |SC#n * | SF#6 | | SF#7 | | SF#8 | * SP#n
| |======================================================>
+----+ * +------+ +------+ +------+ *
* * * * * * * * * * * * * * * * * * * * * * *
SC:Service Chain SP:Service Path
//////////////////////////////////////////////////////////////////////
*How packets traverse*
Service Chain#1:
SP#1
[ CF ]----------->[ SF#1 ]---->[ SF#2 ]----->[ SF#3 ]------->
Service Chain#2:
SP#2
[ CF ]----------->[ SF#4 ]------------------>[ SF#5 ]------->
:
Service Chain#n:
SP#n
[ CF ]----------->[ SF#6 ]---->[ SF#7 ]----->[ SF#8 ]------->
Figure 7: SF Dedicated Model
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3.2.1.2. SF Shared Model
In this model, an SF is shared by multiple SPs. Several SPs are
mixed at shared SFs, and thus this method requires FWDs for
forwarding each packet to the corresponding next hop by identifying
the SP which each packet belongs to. The overview of the SF shared
model is shown Figure 8.
*Path Structure*
+----+ +---+ +----+ +---+ +------+ +---+ +----+
| |SC#1 |FWD| |SF#1| |FWD| |SF#2_1| |FWD| |SF#3| SP#1
| |==============================================================>
| |SC#2 | | | | | | +------+ | | | | SP#2
| |============================# +------+ #======================>
| | | | +----+ | | # |SF#2_2| # | | +----+
| | | | | | #==========# | |
->| CF | +---+ +---+ +------+ +---+
| |
. .
. .
. .
+---+ +----+ +---+ +----+
| |SC#n |FWD| |SF#4| |FWD| |SF#5| SP#n
| |==============================================================>
+----+ +---+ +----+ +---+ +----+
SC:Service Chain SP:Service Path
///////////////////////////////////////////////////////////////////////
*Packet Flow*
Service Chain#1:
SP#1
[ CF ]---->[FWD]-->[SF#1]-->[FWD]-->[SF#2_1]-->[FWD]-->[SF#3]--->
Service Chain#2:
SP#2
[ CF ]---->[FWD]-->[SF#1]-->[FWD]-->[SF#2_2]-->[FWD]-->[SF#3]--->
:
Service Chain#n:
SP#n
[ CF ]---->[FWD]-->[SF#4]--------------------->[FWD]-->[SF#5]--->
Figure 8: SF Shared Model
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3.2.2. Pattern 2: Dynamic Selection of Segmented Service Path
The mechanism of this pattern is shown in Figure 9. The translation
points are CFs and some FWDs. The SP is established by a series of
multiple paths, which are sectioned by CFs and FWDs. The resulting
path is referred to as a segmented path in this draft. CFs or FWDs
that select the next segmented path might require notification of
forwarding configuration information from the CE. Moreover, some
FWDs require functions to select the destination of packets from
various alternatives and to retrieve the information for selecting
the next path. For example, each FWD obtains metric information or
load conditions of servers and selects an optimal segmented path
based on the information. The CE might support the selection
mechanism and may notify CFs or FWDs of it.
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*Path Structure*
+----+ +---+ +----+ +---+ +------+ +---+ +----+
| |SC#1 |FWD| |SF#1| |FWD| |SF#2_1| |FWD| |SF#3| SP#1
| |========================*=====================================>
| | | | | | | # | +------+ | | | | SP#2
| | | | | | | # | +------+ #======================>
| | | | +----+ | # | |SF#2_2| # | | +----+
| | | | | #==============# | |
->| CF | +---+ +---+ +------+ +---+
| |
. .
. .
. .
+---+ +----+ +---+ +----+
| |SC#n |FWD| |SF#4| |FWD| |SF#5| SP#m
| |==============================================================>
+----+ +---+ +----+ +---+ +----+
SC:Service Chain SP:Service Path
///////////////////////////////////////////////////////////////////////
*How packets traverse*
Service Chain#1:
SP#1
[ CF ]---->[FWD]-->[SF#1]-->[FWD]-->[SF#2_1]-->[FWD]-->[SF#3]--->
SP#2
[ CF ]---->[FWD]-->[SF#1]-->[FWD]-->[SF#2_2]-->[FWD]-->[SF#3]--->
:
Service Chain#n:
SP#m
[ CF ]---->[FWD]-->[SF#4]--------------------->[FWD]-->[SF#5]--->
Figure 9: Dynamic Selection of Segmented Service Path
In addition, this pattern supports the establishment of hierarchical
domains discussed below:
3.2.2.1. Hierarchical Service Path Domains
Complex problems often become manageable with a hierarchical
approach. This pattern allows network-wide orchestration of Service
Chaining to be relatively simple, while hiding the complexities of
fine-grained policy-based path selection within sub-domains. Each
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sub-domain can be independently administered and orchestrated. This
architecture is described in [I-D.dolson-sfc-hierarchical].
Figure 10 shows two levels of hierarchy in a service provider's
network. At the top level in the hierarchy, Service Chaining
components are:
1. Edge-classifiers (Edge CF) that reside near the edge of a service
provider's domain.
2. SF sub-domains that reside in data centers.
3. Internal Boundary Nodes (IBNs) that reside in data centers,
linking together the levels of the hierarchy. To the higher
level, sub-domains are viewed as a SF. To the lower level, this
is a classifier and FWD.
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*How packets traverse*
+----+ +-----+ +----------------------+ +-----+
| |SC#1| FWD | | IBN#1 | | FWD |
->| |================* *=====================>
| | +-----+ | # (in DC#1) # | +-----+
| | | V # |
|Edge| |+---+ +---+| Top domain
| CF | * * * * *||CF | * * * * * *|FWD|| * * * * *
| | * |+---+ +-+-+| *
| | * | | | | | | Sub *
| | * +-o-o--------------o-o-+ domain*
| | * SC#1.2 | |SC#1.1 ^ ^ #1 *
| | * +-----+ | | | *
| | * | V | | *
| | * | +---+ +------+ | | *
| | * | |FWD|->|SF#1_1|--+ | *
| | * | +---+ +------+ | *
| | * V | *
| | * +---+ +------+ +---+ +------+ *
| | * |FWD|->|SF#1_2|->|FWD|->|SF#2_1| *
| | * +---+ +------+ +---+ +------+ *
. * * * * * * * * * * * * * * * * * * * * * *
.
| | +-----+ +---------------------+ +-----+
| |SC#n| FWD | | IBN#q | | FWD |
| |=======================================================>
| | +-----+ | (in DC#m) | +-----+
+----+ +---------------------+
(Details of sub-domain #q not shown)
Figure 10: Service Chain Hierarchy in Service Provider Networks
The components within an SF sub-domain are opaque at the top level;
each IBN acts as a single SF node in the top-level domain. A service
path in the top-level domain may visit multiple sub-domains.
At the lower level in the hierarchy, each sub-domain contains an
independently administrated Service Chaining network, generally
comprised of multiple instances of multiple types of hosts, most
likely (but not necessarily) within the same data center. There is
no need for knowledge of the "big picture" at the level of the SF-
sub-domain except as required to forward packets to the other SFs
that are the next hop of each chain.
Note that different encapsulation methods can be used at each layer
in the hierarchy, provided the SF domain-Proxy can translate between
them. For example, MPLS could be used to deliver packets from
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network edge to the SF clusters within data centers, and NSH
[I-D.ietf-sfc-nsh] could be used within the data center.
Details of Top Level of Hierarchy
In this pattern, referring to Figure 11, network-wide Service
Chaining orchestration is only concerned with creating service paths
from network edge points to sub-domains within data centers and
configuring classifiers at a coarse level to get the correct hosts'
traffic onto paths that will arrive at appropriate sub-domains. The
figure shows one possible service chain passing from edge, through
two sub-domains, to network egress.
This top level of orchestration may attach metadata to provide
context from the network edge into the data center.
+------------+
|Sub-domain#1|
| in DC1 |
+----+-------+
|
.------+---------. +--+
+--+ / / | \--|CF|
--->|CF|--/---->' | \ +--+
+--+ / SC#1 | \
| | |
| | .------>|--->
| / / |
\ | / /
+--+ \ | / / +--+
|CF|---\ V / /---|CF|
+--+ '------+---------' +--+
|
+----+-------+
|Sub-domain#2|
| in DC2 |
+------------+
Figure 11: Network-wide view of Top Level of Hierarchy
The orchestration at this top level must ensure bidirectional path
symmetry so that inbound packets traverse sub-domains in the reverse
order as outbound packets.
Because classifiers must have rules to handle any traffic passing
through the network, we believe that a useful approach to
classification will be to assign traffic to service function paths on
the basis of coarse classification like subscriber tier, tenant or
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VRF identifier. These classification rules could be relatively
static, changing in response to provisioning but not in response to
traffic.
In some networks, it might be possible to create a rule per
residential subscriber, resulting in rule updates when subscribers
are assigned IP addresses. However, with judicious allocation of IP
blocks, entire classes of subscribers could be classified with IP-
prefix rules. Similarly, in a mobile network path selection could be
based on the APN (Access Point Name) identifier.
Hence, there are methods of globally managing very large networks by
choosing a suitable classification granularity.
Details of Lower Levels of Hierarchy
Within each SF sub-domain, there are:
1. An IBN to receive incoming data packets on any of the configured
service chains and load-balance (if necessary) traffic to
classifiers,
2. Classifier(s) to select internal service chain to use,
potentially based on stateful flow analysis, DPI, etc.
3. Service components comprised of FWD and SF.
Local Service Chaining orchestration is concerned with providing
viable paths to various functions, providing failure recovery, NFV
elasticity, etc.
Classification within each sub-domain can be concerned with
determining the local service paths for individual transport-layer
flows based on ports, DPI and meta-data provided by the higher-level
chain.
For any classifier that is transport-layer-stateful, it is most
efficient for the same classifier instance to handle traffic in both
directions of a bidirectional connection. State tracking may require
that service function paths begin and terminates at the same node
with the flow state, where the same classifier instance can be used
for both directions of traffic.
4. Consideration on Forwarding Methods and Paths Selection Patterns
This chapter presents the results of analyzing the forwarding methods
and architecture patterns in chapter 3.
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4.1. Analysis of Forwarding Methods
4.1.1. Analysis of Method 1: Using Flow Identifiable Information
Data Plane Aspects
This method can achieve Service Chaining without changing packet
format, such as attaching any header on packets, so it may not
imply any overhead or be subject to MTU restrictions.
Furthermore, this method does not require additional functions for
SFs to apply or handle any header because data packets are
transported unaltered. Therefore, it will be easier to use legacy
SFs for network operators.
On the other hand, it is difficult to forward a packet to same
FWDs several times because flow identifiable information is not
basically changed in the forwarding processes. For example,
distinction of incoming ports will be required for FWD to resolve
the next hop appropriately when a packet traverses it several
times.
Control Plane Aspects
This method might be achieved by using existing control
mechanisms. For example, openflow, which is able to provide
flexible forwarding control, would be available for creating SPs.
However, this methoed might require FWDs to configure forwarding
entries for each flow to each FWD. For example, if there are
10,000 flows to be handled at a CF/FWD, the forwarding table for
each CF/FWD uses 10,000 flow entries at most. Therefore, it might
not be feasible for large-scale networks such as carrier networks
that handle a SC per user (which means that individual users will
be associated with different policies), because some large
carriers have over a million users and even more flows. In
addition, control signaling would increase because forwarding
configuration for each flow to each FWD is required. Moreover, it
may be hard to use this method if some SFs modify header fields of
a packet or frame, for example, NAT/NAPT, in a chain. For
example, if a NAT changes the IP address of packets dynamically,
the FWDs that follow need to renew their forwarding tables. This
method also have restriction about forwarding based on high-layer
information, such as application information in packet payload.
The process of detecting high-layer information is usually heavy
compared with L2 or L3 forwarding process, and most existing
forwarding functions have capability to refer only under L4
headers. Therefore, it will be difficult to use this method to
forward packets along SPs decided by detecting high-layer
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information since individual L2-4 packet headers may not retain
enough information. An example of this type of problem is a video
streaming imbedded within a web page. The identifiable
information at the L2-4 level does not allow differentiation
between the video stream and the rest of the frame, and thus the
all traffic on the web page is forwarded following the same SC.
The results of the above analysis suggest that, although this method
is beneficial in terms of impact to existing network, it would not be
scalable. Therefore, this method might be suitable for networks with
a limited number of flows.
Measurements taken in multiple residential service providers'
networks indicate that for each 1Gbps of traffic the sustained rate
of new flows can range from 1,000 flows/s to 30,000 flows/s. From
this, for example, there would be between 10,000 and 300,000 new
flows/s on a 10 Gbps link. Therefore, in some networks at some times
of day, this method using 5-tuple as flow identifiable information
would require sustaining up to 300,000 table updates per second for
each FWD. This incurs a significant amount of control traffic and
computational effort.
4.1.2. Analysis of Method 2: Stacking Headers
Data Plane Aspects
In this method, SP information is attached on each packet as
headers for forwarding, and the number of the headers increases
depending on the number of SFs which the packet will traverse.
This means that the size of each packet increases. Packet sizes
may be restricted by the minimum available MTU of any link in the
network and exceeding the MTU will require to fragment the
original packets. Fragmentation adds a new source of errors and
may require forwarding processes to be more complex. For example,
the whole original packet will be discarded even if one of
fragments of the packet gets lost, or in terms of SF equipment, it
would be very wasteful of CPU if fragmented packets need to be
reassembled at every SF resources, and some equipment has
restricted resources and memory for reassembly. Fragmentation
will also cause an increase in traffic as more packets have to be
processed by the network.
Moreover, this method requires SF to be applied to the headers
because they receive packets with optional headers. Therefore SFs
will be required to be able to recognize the headers, or proxy
functions, which remove the headers before inserting packets into
SFs and re-attach the appropriate headers on the returned packet,
will be required. In addition, when a SF is used by multiple SCs,
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it will be challenging for SFs to process packets because header
length attached on each packet may vary and SFs are required to
have a mechanism to recognize the header length for each packet.
Control Plane Aspects
In this method, none of the FWDs require any specific forwarding
tables for Service Chaining or interface to receive forwarding
configuration information. In short, FWDs are stateless or
eliminated at hops, and this method has advantages of high scale
in SPs managements and lower latency. In addition, no CEs will be
required to manage the forwarding configuration of FWDs for
Service Chaining, and so the control mechanism might become simple
compared with other methods.
On the other hand, some relay nodes such as switches or SFs are
required to have a function to remove the outermost header from
the received packets. FWDs also don't have to identify flows or
services, so cannot change the following SPs. Moreover, CF must
grasp all of addresses of relay nodes which packets will traverse,
and it will require any CE to manage addresses of relay nodes and
a link between CF and the CE. There are already several existing
technologies that can be used to achieve this method, such as
segment routing.
The results of the above analysis indicate that this method would be
appropriate when the number of SFs in a SC is small, and most SFs are
deployed in a single domain. On the other hand, it may be unsuitable
in cases where there are many SFs in a chain, or packets have to
traverse multiple domains.
4.1.3. Analysis of Method 3: Using Service Chain Identifier
Data Plane Aspects
The common features of this method and the individual features of
each approach to map service chain identifiers in terms of data
plane aspects are described below.
o Common features of method3
In this method, a service chain identifier, defined for each
SC, is mapped into each packet. FWDs recognize the next hops
of received packets from the identifiers independent of any
information of original packets. Therefore, SFs which modify
original packet format can also be used. In addition, it is
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easy to change the following SPs on a route by renewing the
identifier.
On the other hand, attachment of an identifier might expand
packet size, and it would cause an increase of traffic amount
or problems which happens as a result of exceeding MTU (The
problems are stated in Section 4.1.2.). However, by adopting a
single fixed-length identifier, the problems might be
prevented. Or, when overloading the identifier on an existing
field, such as MAC address, packet size is not changed and such
issues would not occur.
Moreover, forwarding along SPs is provided based on service
chain identifiers, and so if there are network nodes which are
unaware of the identifiers, such as routers without functions
to forward packets based on the identifiers, in a SC domain,
some tunnel would be required for passing packets over them.
o Tagging an extra header:
In this approach, the identifiers are prepended to packets, and
so a single mapping mechanism could be used independently of
the formats of the target packets.
Conversely, this approach requires SFs to parse the extra
headers (Problems which happens as result of inserting packet
with optional headers into SFs are stated in Section 4.1.2).
In case that an existing header, which SFs can recognize, is
used as a service identifiable tag, this problem might be
restricted. For example, some SFs can recognize VLAN- tags,
and they would not need any improvement for the SFs if they are
used as service identifiable tags. However, using an existing
header might have some effects on the original uses.
o Inserting into an optional field:
In this approach, service chain identifiers are inserted in
some field of the original packets, and the packets seem normal
formats from SFs. Therefore, any improvement for enabling SFs
to handle the identifiers would not be required.
Meanwhile, identifier insertion or packet forwarding mechanisms
would vary depending on the formats of the original packets,
because positions where identifiers are inserted are different
for each packet format. For example, optional field positions
of IPv4 and IPv6 headers are different. Furthermore,
especially, the inserting approach, using IPv4 optional fields,
might have some problems. For example, some server OS and
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applications strip the IPv4 optional field due to security
concerns. Therefore, it appears this is a difficult solution
for IPv4 networks.
Also, in case that existing field is used for storing the
identifier, amount of identifier information might be small
compared with tagging an extra header approaches.
o Overloading on a destination or source address:
In this approach, a destination or source address is used for
identifying service chain which the packet belongs to in
addition to original usage, and so packets size increase caused
by attaching additional headers does not occur. Also, any
improvement for enabling SFs or any other network equipment to
handle the identifiers would not be required, because the
packets seem normal formats from them. In other words, this
approach can coexist with legacy equipment.
Meanwhile, the addresses for Service Chaining are overwritten
on the original address in this approach, and so an additional
encapsulation would be required during the Service Chaining
process when retaining the original address information.
Therefore, for cases when L2 or L3 addresses are used for
identifying subscribers, the overloading approach might require
the MTU expansion for additional encapsulation. Moreover, when
using L2 addresses as service chain identifier and sending
packets to another L2 domain across a L3 domain, an extra means
such as L3 tunnel is required.
Control Plane Aspects
The common features of this method and the individual features of
the overloading approach in terms of control plane aspects are
described below.
o Common features of method3
This method enables FWDs to save resources for managing
forwarding tables and allows all SPs to be established in
advance in most of cases. This prevents an increase of control
signals such as openflow or Gx/Sd, and also enables changing
the following SPs without changing forwarding configuration of
FWDs.
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On the other hand, this method requires a new control mechanism
based on service chain identifiers, therefore, FWDs, CE and
interface between them have to be updated to apply forwarding
configuration based on the identifiers.
o Overloading on a destination or source address:
Overloading approach might be achieved without new control
mechanisms or drastic remodeling of existing control entities.
For example, MAC chaining can be established by using
programmed standard openflow switches.
On the other hand, in the overloading approach, each SP is
composed of a set of unique addresses, and thus FWDs are
required to have addresses as many as service chains which pass
through them.
The results of the above analysis indicate that this method has many
advantages in terms of scalability, and it might be appropriate for
use in large-scaled networks in which there are so many SFs and
various types of flows. On the other hand, when the identifier
handling mechanism is an entirely new architecture such as
SFC[RFC7665], renewal or introduction of several equipment such as
FWDs and CE will be required.
4.2. Analysis of Service Path Selection Patterns
4.2.1. Analysis of Pattern 1: Static SP Selection
In this pattern, the mechanism of FWDs would be simpler than the one
in pattern 2 because FWDs do not require any functions to select
paths or retrieve any information for next hop resolution purposes.
Moreover, it is not necessary to maintain the state of each flow.
Therefore, existing network virtuarizing techniques, such as VxLAN or
MPLS, can be used to achieve Service Chaining in this pattern.
Especially, network slicing model does not require any special
forwarding mechanisms.
On the other hand, this pattern has restriction in the management of
SPs. When adding new SFs to a SC, removing SFs from a SP, or
migrating SFs to other locations, re-establishment of SP would be
required. This restriction in network slicing model would be more
strict because this model need to establish a new network for adding
a SP. For relaxing the restriction, it is desirable to use this
pattern together with a means, such as load balancer, which enable to
add the same kind SFs into a SP without changing the configuration of
the SP. Or the restriction would be relaxed when network
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virtuarizing technique progresses significantly and network operaters
can install SFs more freely.
In addition, this pattern would also have restriction for use in wide
area networks which include multiple domains. This pattern requires
unified management of FWDs and SFs, in an SC domain, for setting end-
to-end paths. Therefore, the management system of SPs, for example,
a CE, for wide-area networks that include several segments might be
massive and complex. Figure 12 shows the case in which SPs are
established across multiple datacenters in pattern 1. In this case,
a CE (or a set of CEs) manages multiple datacenters as a single SC
domain for establishing SPs across the datacenters.
+--------------+
. . . . . . . . . . |Control Entity| . . . . .
. . +--------------+ .
. . .
* * . * * * * . * * * * * * * * * * * * * * * * . * * * * * * * * *
* . . . *
* . . . *
* . .-----. .-----------. .-----. *
* +----+ / DC#1 \ / WAN \ / DC#2 \ *
* | |=====================================================> SP#1 *
* | CF |=====================================================> SP#2 *
* : : : *
* | |=====================================================> SP#n *
* +----+ \ / \ / \ / *
* '-----' '-----------' '-----' *
* *
* SC Domain *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Figure 12: Establishment of SPs across Multiples DCs in Pattern 1
4.2.2. Analysis of Pattern 2: Dynamic SP Selection
In this pattern, SPs are established with a combination of segmented
paths, so it enables SPs to be established flexibly (which means, CEs
do not need to constantly manage the entire end-to-end SP) based on
additional information such as the SF load conditions.
Furthermore, as described in the previous section, in cases where
some SPs traverse multiple datacenters across a WAN, SPs could be
established with a combination of segmented paths that each
datacenter determines independently based on the Service Chain
information. Therefore, it might be possible to separate SC domains
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into several small areas for WANs, which would enable a simpler
configuration of each CE. Figure 13 shows the case in which SPs are
established across multiple datacenters in pattern 2. In Figure 13,
each CE manages a single datacenter independently, and the CEs
synchronize the Service Chain information for establishing and
determining the appropriate segmented SPs in each domain.
However, the (fault) monitoring of the whole SC can become more
difficult, as multiple domains are part of the SC. On the other
hand, each domain can perform its management as required (and this is
probably better as it is more specific). This will require an
overarching (fault) monitoring where information from multiple SC
domains is collected and aggregated to get a full view of the end-to-
end service of the SC.
Moreover, in this pattern, some FWDs may require additional
mechanisms to select the next segmented path, and the FWDs must
maintain the states of each flow because some SFs require a stateful
process, and the FWDs need to insert packets into the same SF
instances in the same session.
In case that SC information is conveyed to some components via data
plane as any encapsulation, a new protocol such as SFC [RFC7665] will
be required.
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Synchronization of
Service Chain info.
+--------------------------------------+
| |
v v
+--------+ +--------+
| CE#1 | | CE#2 |
+--------+ +--------+
. .
* * * * * * . * * * * * * * * * * * * . * * * * * *
* . * * . *
* .-------------. * * .------------. *
* / DC#1 \ * .------. * / DC#2 \ *
* +----+ +-----+ * / WAN \ * +-----+ | *
* | |=========>| | * | | * | CF/ |==========> SP#1 *
* | CF |=========>| FWD |===============>| FWD |==========> SP#2 *
* : : : * | | * : : : *
* | |=========>| | * \ / * | |==========> SP#n *
* +----+ +-----+ * '------' * +-----+ | *
* \ / * * \ / *
* '-------------' * * '-----------' *
* SC Domain#1 * * SC Domain#2 *
* * * * * * * * * * * * * * * * * * * * * * * * * * * *
Figure 13: Establishment of SPs Across Multiples DCs in pattern 2
Also, the detailed analysis of the establishment of "Hierarchical
Service Path domains" is shown in the following section.
4.2.2.1. Analysis of Hierarchical Service Path domains
The dynamic selection of SPs pattern allows multiple independent
domains of administration. (In the example, two levels were shown,
but the pattern could be extended to multiple levels.)
This pattern allows even the largest networks to implement SC from
the edges of the network by using coarse-grained classification.
Classification choices can be made that are feasible within the
constraints of the edge classifiers and FWDs. There is no need to
maintain flow state or react to traffic at the top level.
This pattern allows control of sub-domains to be delegated to
different owners. Each domain is simpler to comprehend than would be
the case by dealing with a single flat network. Furthermore,
failures and errors are localized (See Figure 14.).
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+----------+
|Top-level | . . . . . . . . . . . . . . . . . . . . .
|Control | .
|Entity | +------------+ +--------+ .
+----------+ |sub-domain#1|. . .| CE#1 | .
. +-----+------+ +--------+ .
. | .
. .------+---------. +---+ .
. +---+ / \--|CF |. . . .
. . . .|CF |--/ \ |FWD| .
. |FWD| / \+---+ .
. +---+ | | .
. | | .
. | | .
. +---+ \ / .
. |CF | \ / +---+ .
. . . .|FWD|---\ /---|CF | . . .
+---+ '------+---------' |FWD|
| +---+
+--------+ +------------+
| CE#2 |. . .|sub-domain#2|
+--------+ +-----+------+
Figure 14: Multiple Control Entities in Hierarchical Service Chaining
This hierarchical model supports the management of large networks by
adhering to these principles:
1. At higher levels of hierarchy, packet classification is coarse,
to minimize state and control-plane chatter.
2. At lower levels of hierarchy, packet classification can be more
granular because classifiers in the lower levels deal with a
subset of the entire network: fewer flows, lower bit-rate and a
subset of network policy.
However, in this model, a new component that can proxy between the
different domains, termed "Internal Boundary Node (IBN)," will be
required. It has some commonality with the legacy SF proxy discussed
in [I-D.song-sfc-legacy-sf-mapping].
This model also requires some coordination of path information within
the IBN, since the IBN must map packets back and forth between
domains. Solving this probably requires sharing metadata
dictionaries among controllers and inventing a scheme that provides a
level of indirection by naming path identifiers and metadata values.
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4.3. Example of selecting Methods and Patterns
In this section, clarifications about the most suitable method and
pattern are made for the following example networks based on the
results of the above analysis.
4.3.1. Example#1: Enterprise Datacenter Network
The conditions of the target network are as follows:
Network type: Network with a single DC.
Intended service: For providing several network service to traffic
of one or several business offices.
Variation of service: A group of adopting network service varies per
office.
The number of SFs included in a service chain: Less than 5 (ref.
section 3.2.1. Sample north-south service function chains in
[I-D.ietf-sfc-dc-use-cases]).
Features of SFs: SFs are set statically, and SFs are exclusively
used for each service.
On the basis of the conditions "network type" and "features of SFs",
pattern 1 with SF dedicated model would be selected.
As the condition "variation of service" describes, such network
requires few flow entries for each FWD, so method 1 would be
applicable. Method 1 also does not require SFs to have any
additional mechanism to apply any header, thus the impact of
implementing this method would be less than other methods.
4.3.2. Example#2: Current Mobile Service Providers Network
The conditions of the target network are as follows:
Network type: Network with a single DC (e.g., (S)Gi-LAN (3GPP,
[TS.23.203])).
Intended service: For providing network access service and several
network service to traffic of millions customers.
Variation of service: Service varies per user or applications.
The number of SFs included in a service chain: Around 5(ref.
examples of service in [I-D.ietf-sfc-use-case-mobility].).
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Features of SFs: Many SFs are hardware equipment and they are
deployed statically. Also, many SFs are used for several service.
A function to inspect user traffic in detail, such as TDF (3GPP,
[TS.23.203]), is located at the ingress of the network, and it
might behave as a CF.
On the basis of the conditions "network type" and "features of SFs,"
pattern 1 with SF shared model would be selected. In such network,
classification based on deep packet inspection such as application
type inspections is done, and paths branching will not be happen.
As the other conditions describe, the operator must handle millions
of flows and the flows traverse multiple SFs, so method 3 would be
applicable. Configuring such amounts of flows among large scale
network might be too much work for operators.
The examples of concrete service of such network are described as
follows:
1. HTTP Modification
Packet Gateway(P-GW), which is defined in 3GPP (ref. [tS.23.203]),
detects traffic to the specific website and that traffic must be
sent through a special element to insert additional data to the
HTTP header or advertisement to the HTTP traffic, so the
destination site can apply specific deals with the operator's
customer (simplify DRM, premium service, etc.) That would require
flow entries with mobile source IP, destination IP and port.
2. VoLTE Calls
VoLTE calls are sent via a special SP. The VoLTE control plane
selects all application network elements. But to reach
application network elements it fully relies on standard routing
and switching mechanisms. With Service Chaining it is possible to
select the SP which can provide required QoS. That would require
to set flow entries with mobile source IP, destination IP and
port.
3. Secure Internet Access
Some customers' HTTP traffic is forwarded to one or more security
functions to inspect for malware. This case would require flow
entries with source IP, destination IP and port.
4. Content Optimizer
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Based on the policy rules, a SC/SP with the Content Optimization
might be provided. Content optimization primarily affects video
and HTTP traffic, and saves valuable radio resources in the
specific radio cells during times of congestion. A controller
might monitor Key Performance Indicators (KPIs) of the radio
network to detect congestion. When congestion is detected, the
controller might enforce a content optimization policy for the
users on the congested radio cell. Most resource-expensive
traffic can be transcoded by a content optimizer to save
bandwidth. Selecting traffic for optimization would require to
set flow entries with mobile source IP, destination IP and port.
Also, content optimization might require changing SCs/SPs assigned
to users flows based on the result of KPI monitoring or the time
of day.
On the other hand, method 1 might be also selected with pattern 1
with SF dedicated model. For example, the series of the above
service might be achieved by static configured flow entries, for
example, with incoming port. However, it will require many incoming
ports for FWDs when the operator would like to share a SF with
multiple SCs, and it will not be scalable.
4.3.3. Example#3: Fixed and Mobile Converged Service Providers Network
The conditions of the target network are as follows:
Network type: Network with multiple DCs (e.g., SFs are deployed at
multiple DCs based on their applications).
Intended service: For providing network access service or several
network service to traffic of millions customers.
Variation of service: Service varies per user. Also, the service
assigned to each flow might vary based on using applications.
The number of SFs included in a service chain: More than 5.
(Various services such as enriched security service and value
added services would be provided)
Features of SFs: Many SFs are deployed as VNFs (Virtualized Network
Functions), and some SFs are shared with multiple SCs. Also, some
SFs changes the following SPs dynamically based on the result of
the process.
On the basis of the conditions "network type" and "features of SFs,"
pattern 2 would be selected. Pattern 2 allows hierarchical approach
which enables operators to deploy SFs in multiple domains easily
based on service requirements. For example, operators can deploy SFs
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into several domains based on application types. This concept is
introduced in [I-D.ietf-sfc-dc-use-cases].
From the above conditions describe, the operator must handle enormous
flows and paths branching, thus method 3 will be appreciable for such
network. Especially, security scenario sometimes requires paths
branching based on the result of packet inspection such as processes
of DPI or traffic analyzer. Some security functions such as web
application firewall (WAF) are specialized for each application, and
it might be inefficient to insert all traffic into such SFs.
Therefore, for inserting only target packets to appropriate security
functions, classifying and paths branching based on packet inspection
would be required.
5. Acknowledgements
The authors would like to thank Konomi Mochizuki and Lily Guo for
their reviews and comments.
6. Contributors
The following people are active contributors to this document and
have provided review, content and concepts (listed alphabetically by
surname):
Poul Bottorff
Hewlett Packard Networking
Mohamed Boucadair
France Telecom
Nicolas Bouthors
Qosmos
Hiroshi Dempo
NEC
Christian Jacquenet
France Telecom
Ron Parker
Affirmed Networks
Chuong D. Pham
Telstra
Paul Quinn
Cisco Systems
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7. IANA Considerations
This memo includes no request to IANA.
8. References
[I-D.dolson-sfc-hierarchical]
Dolson, D., Homma, S., Lopez, D., Boucadair, M., and D.
Liu, "Hierarchical Service Function Chaining", draft-
dolson-sfc-hierarchical-04 (work in progress), December
2015.
[I-D.fedyk-sfc-mac-chain]
Bottorff, P., don.fedyk@hpe.com, d., and H. Assarpour,
"Ethernet MAC Chaining", draft-fedyk-sfc-mac-chain-01
(work in progress), January 2016.
[I-D.ietf-sfc-dc-use-cases]
Surendra, S., Tufail, M., Majee, S., Captari, C., and S.
Homma, "Service Function Chaining Use Cases In Data
Centers", draft-ietf-sfc-dc-use-cases-04 (work in
progress), January 2016.
[I-D.ietf-sfc-nsh]
Quinn, P. and U. Elzur, "Network Service Header", draft-
ietf-sfc-nsh-02 (work in progress), January 2016.
[I-D.ietf-sfc-use-case-mobility]
Haeffner, W., Napper, J., Stiemerling, M., Lopez, D., and
J. Uttaro, "Service Function Chaining Use Cases in Mobile
Networks", draft-ietf-sfc-use-case-mobility-05 (work in
progress), October 2015.
[I-D.song-sfc-legacy-sf-mapping]
Song, H., You, J., Yong, L., Jiang, Y., Dunbar, L.,
Bouthors, N., and D. Dolson, "SFC Header Mapping for
Legacy SF", draft-song-sfc-legacy-sf-mapping-06 (work in
progress), August 2015.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
DOI 10.17487/RFC3022, January 2001,
<http://www.rfc-editor.org/info/rfc3022>.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <http://www.rfc-editor.org/info/rfc6146>.
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[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, DOI 10.17487/RFC6296, June 2011,
<http://www.rfc-editor.org/info/rfc6296>.
[RFC7498] Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for
Service Function Chaining", RFC 7498,
DOI 10.17487/RFC7498, April 2015,
<http://www.rfc-editor.org/info/rfc7498>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<http://www.rfc-editor.org/info/rfc7665>.
Authors' Addresses
Shunsuke Homma
NTT, Corp.
3-9-11, Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Phone: +81 422 59 3486
Email: homma.shunsuke@lab.ntt.co.jp
Kengo Naito
NTT, Corp.
3-9-11, Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Email: k.naito@nttv6.jp
Diego R. Lopez
Telefonica I+D.
Don Ramon de la Cruz, Street
Madrid 28006
Spain
Phone: +34 913 129 041
Email: diego.r.lopez@telefonica.com
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Martin Stiemerling
NEC Laboratories Europe / Hochschule Darmstadt
Kurfuerstenanlage 36
Heidelberg 69115
Germany
URI: ietf.stiemerling.org
David Dolson
Sandvine
408 Albert Street
Waterloo, Ontario N2L 3V3
Canada
Email: ddolson@sandvine.com
Alexey Gorbunov
Nokia
6000 Connection Drive
Irving, Texas 75039
USA
Phone: +1 214 516 11 41
Email: Alexey.gorbunov82@gmail.com
Nicolai Leymann
DT
Winterfeldtstrasse 21-27
Berlin 10781
Germany
Phone: +49 (0)30 835392761
Email: n.leymann@telekom.de
Paul Bottorff
Hewlett Packard Enterprise
8000 Foothills Blvd.
Roseville, CA
USA
Email: paul.bottorff@hpe.com
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Don Fedyk
Hewlett Packard Enterprise
153 Taylor Street
Littleton, MA
USA
Email: don.fedyk@hpe.com
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