Service Function Chaining S. Homma
Internet-Draft K. Naito
Intended status: Informational NTT
Expires: April 30, 2015 D. R. Lopez
Telefonica I+D
October 27, 2014
Analysis on Forwarding Methods for Service Chaining
draft-homma-sfc-forwarding-methods-analysis-00
Abstract
Some working groups of the IETF and other Standards Developing
Organizations are now discussing use cases of a technology that
enables data packets to traverse appropriate service functions
through networks. This is called Service Chaining in this document.
(Also, in Network Functions Virtualisation (NFV), a subject that
forwarding packets to required service functions in appropriate order
is called VNF Forwarding Graph.) This draft does not focus only on
SFC method, and thus, use the term "Service Chaining". SFC may be
one method to realize Service Chaining. There are several Service
Chaining methods to forward data packets to service functions, and
the applicable methods will vary depending on the service/network
requirements of individual networks.
This document presents the results of analyzing packet forwarding
methods and path decision patterns for achieving Service Chaining.
For forwarding data packets to the appropriate service functions,
distribution of route infromation and steering data packets following
the route infromation, are required. Examples of route information
are packet identifier and the routing configurations based on the
identifier. Also, forwarding functions are required to decide the
path according to the route information.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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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 April 30, 2015.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 4
3. Classification of Forwarding Methods and SP Decision Patterns 5
3.1. Forwarding Methods . . . . . . . . . . . . . . . . . . . 5
3.1.1. Method 1: Forwarding Based on Flow Identifiable
Information . . . . . . . . . . . . . . . . . . . . . 5
3.1.2. Method 2: Forwarding with Stacked Transport Headers . 6
3.1.3. Method 3: Forwarding Based on Service Chain
Identifiable Tags . . . . . . . . . . . . . . . . . . 7
3.2. Service Path Decision Patterns . . . . . . . . . . . . . 9
3.2.1. Pattern 1: End to End Static Service Path . . . . . . 9
3.2.2. Pattern 2: Dynamically Determined Service Path . . . 11
4. Consideration of Service Chaining Methods and Architecture
Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Analysis of 3.1. Forwarding Methods . . . . . . . . . . . 13
4.1.1. Analysis of Method 1 . . . . . . . . . . . . . . . . 13
4.1.2. Analysis of Method 2 . . . . . . . . . . . . . . . . 13
4.1.3. Analysis of Method 3 . . . . . . . . . . . . . . . . 14
4.2. Analysis of 3.2. Determination of Service Paths . . . . . 14
4.2.1. Analysis of Pattern 1 . . . . . . . . . . . . . . . . 14
4.2.2. Analysis of Pattern 2 . . . . . . . . . . . . . . . . 15
4.3. Example of selecting Methods and Patterns . . . . . . . . 16
4.3.1. Example A: Datacenter Network . . . . . . . . . . . . 17
4.3.2. Example B: Current Mobile Carrier Network . . . . . . 17
4.3.3. Example C: Fixed Mobile Convergence Network . . . . . 18
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
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6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 18
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
Service Chaining is a technology that enables data packets to
traverse the appropriate service functions deployed in a network.
This draft assumes that Service Chaining is achieved in the following
steps:
a. A classification function identifies data packets and determines
the set of services that will be provided for the packets and in
which order.
b. The path, that the packets will traverse for reaching the required
service functions, is established based on the result of step a.
c. Forwarding functions determine the appropriate destination and
forward each packet to the next hop according to the path.
d. A service function provides services to received packets and
return each packet to the 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 and the patterns used to
decide the paths will affect the mechanism of Service Chaining as
well as 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 analyzing forwarding
methods for Service Chaining.
OAM, security, and redundancy are outside the scope of this draft.
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2. Definition of Terms
Term "Classification", "Classifier" referred to draft-merged-sfc-
architecture-01. Term "Service Function", "Service Node" referred to
draft-ietf-sfc-dc-use-cases-01.
Service Chaining: A technology that lets data packets traverse a
series of service functions.
Classification: Locally instantiated policy and customer/network/
service profile matching of traffic flows for identification of
appropriate outbound forwarding actions.
Classifier (CF): The entity 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.
Service Node (SN): A virtual or physical device that hosts one or
more service functions, which can be accessed via the network
location associated with it.
Forwarder (FWD): The entity, responsible for forwarding data packets
along the service path, which includes delivery of traffic to the
connected service functions. FWD handles Forwarding Tables, which
is used for forwarding packets.
Control Entity (CE): The entity 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 user packets selected as
a result of classification. The implied order may not be a linear
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progression as the architecture allows for nodes that copy to more
than one branch.
Service Path (SP): The instantiation of a service chain in the
network. Packets follow a service function path through the
requisite service functions. SP shows a specific path of
taraversing SF instance. 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.
Service Chaining Domain (SC Domain): The domain managed by one or a
set of CEs.
Service Path Information (SPI): The information used to forward
packets to The appropriate SFs based on the selected service.
Examples of SPI include routing configurations for Forwarders,
transport headers for forwarding packets to required SFs, and
service/flow identifiable tags.
3. Classification of Forwarding Methods and SP Decision Patterns
3.1. Forwarding Methods
In Service Chaining, data packets are transferred to service
functions, which can be located outside the regular computed path to
the original destination. Therefore, a routing mechanism that is
different from general L2/L3 switching/routing may be required. The
routing mechanism can be classified into three methods in terms of
distribution of SPI and packet forwarding.
3.1.1. Method 1: Forwarding Based on Flow Identifiable Information
The mechanism of method 1 is shown in Figure 1. In this method,
routing configurations 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 may be an CE to handle this.
The flow identifiable information can be constructed with some fields
of L2 or L3 or combination of those. 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
identifable information and forwards the packets to the SFs according
to the configuration. This method does not require changing any
fields of the original packet frame.
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*Distribution model of SPI*
+----------------+
| 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 |
+-------+ +-------+ +-------+ +-------+
Fig.1 Forwarding Based on Flow Identifiable Information
3.1.2. Method 2: Forwarding with Stacked Transport Headers
The mechanism of method 2 is shown in Figure 2. In this method, the
CF classifies packets and stacks transport headers, e.g., MPLS or GRE
headers, onto the packets based on the classification. The
configuration about how FWDs handle the headers is pre-configured.
Each FWD forwards the packets to SFs following the outermost header.
The outermost header is removed after each forwarding or service
process. The actions are repeated until all headers are removed.
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*Distribution model of SPI*
+----------------+
| 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 FWD1 * the outermost transport 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 |
+--------+ +--------+ +--------+ +--------+
Fig.2 Forwarding with Stacked Multiple Transport Headers
3.1.3. Method 3: Forwarding Based on Service Chain Identifiable Tags
This method is shown in Figure 3. In this method, a CF classifies
each packet and attaches a tag for identifying the service or flows
on the packets based on the classification. The routing
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configuration based on the tags is sent to each FWD (from some CE) in
advance. Each FWD fowards packets to the SFs following the
configuration and the tag. After a packet has traversed all SFs, the
tag is removed.
*Distribution model of SPI*
+----------------+
| 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 FWD1
->Stack ID#2
... ... ...
//////////////////////////////////////////////////////////////////////
*Condition of Packet*
Locate: [CF] [FWD] [SF#1] [FWD]
+-------+ +-------+ +-------+ +-------+
Tag: | ID#1 | | ID#1 | | ID#1 | | ID#1 |
+-------+ +-------+ +-------+ +-------+
Packet:| PDU | | PDU | | PDU | | PDU |
+-------+ +-------+ +-------+ +-------+
Fig.3 Forwarding Based on Service Chain Identifiable Tags
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3.2. Service Path Decision Patterns
Since Service Chain contains only logical information (e.g. series of
services that are applied to flows and their sequences), the actual
instances, which are called Service Paths, are needed in order for
the forwarding process to work. In this process, an instance of
Service Path is created at certain points during a packet's delivery.
Therefore, to forward packets, the Service Chain needs to be turned
into an SP, which indicates specific FWDs (or switches, routers) and
SFs that the packets will be forwarded to. In the Service Chain to
SP change points, the paths that determine the Service Chaining are
classified into two patterns.
3.2.1. Pattern 1: End to End Static Service Path
The translation point is only a CF; that is, the SP is statically
pre-established as an end-to-end path. A CF inserts packets into the
appropriate pre-established path based on their classification. Each
FWD on the route has a routing table to uniquely determine the next
destination of packets, and each FWD statically forwards the received
packets to the next destination. FWDs require only a function to
receive indications of routing configurations from the CE. Pattern 1
can be achieved in the following ways.
3.2.1.1. SF Shared Model
Figure 4 shows the mechanism of this way. An SF is shared by
multiple SPs. In this way, the FWDs require a function to identify
packets and insert the packets into the next appropriate hop.
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*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
////////////////////////////////////////////////////////////////////////////
*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 ]-->
Fig.4 SF Shared Model
3.2.1.2. SF Dedicated Model
Figure 5 shows the mechanism of this style. An SF (instance) is used
by only one single SP; in other words, there is an SF instance per
SP. At each FWD, incoming packets are statically routed to a single
predefined next hop.
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*Path Structure*
+----+ +-----+ +------+ +-----+ +------+ +-----+ +------+
| |SC#1| FWD | |SF#1_1| | FWD | |SF#2_1| | FWD | |SF#3_1|SP#1
| |===================================================================>
| | +-----+ +------+ +-----+ +------+ +-----+ +------+
| | +-----+ +------+ +-----+ +------+ +-----+ +------+
| |SC#2| FWD | |SF#1_2| | FWD | |SF#2_2| | FWD | |SF#3_2|SP#2
| |===================================================================>
->| CF | +-----+ +------+ +-----+ +------+ +-----+ +------+
| |
. .
. .
. .
+-----+ +------+ +-----+ +------+
| |SC#n| FWD | | SF#4 | | FWD | | SF#5 |SP#n
| |===================================================================>
+----+ +-----+ +------+ +-----+ +------+
SC:Service Chain
/////////////////////////////////////////////////////////////////////////////
*How packets traverse*
Service Chain#1:
SP#1
[ CF ]--->[ FWD ]-->[SF#1_1]-->[ FWD ]-->[SF#2_1]-->[ FWD ]-->[SF#3_1]-->
Service Chain#2:
SP#2
[ CF ]--->[ FWD ]-->[SF#1_2]-->[ FWD ]-->[SF#2_2]-->[ FWD ]-->[SF#3_2]-->
:
Service Chain#n:
SP#n
[ CF ]--->[ FWD ]-->[ SF#4 ]----------------------->[ FWD ]-->[ SF#5 ]-->
Fig.5 SF Dedicated Model
3.2.2. Pattern 2: Dynamically Determined Service Path
The mechanism of this style is shown in Figure 6. The translation
points are a CF and FWDs. The SP is established by a series of
multiple paths, which are sectioned by CFs and FWDs. Each path
determined by CFs and FWDs is referred to as a segmented path in this
draft. CFs or FWDs that determine the next segmented path may
require notification of routing configurations 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
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information or load conditions of servers and selects an optimal
segmented path based on that information. The CE may have the
selection mechanism and may notify CSs/FWDs of it.
*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
////////////////////////////////////////////////////////////////////////////
*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 ]-->
Fig.6 Dynamically Determined Service Path
4. Consideration of Service Chaining Methods and Architecture 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 3.1. Forwarding Methods
4.1.1. Analysis of Method 1
This method can achieve Service Chaining without adding any headers
to packets, so it may not cause any increase in packet size or be
subject to MTU restrictions. Furthermore, this method does not
require additional functions within SFs to be applied to any headers
because data packets are transported in original format. Therefore,
it will be easier to use legacy SFs for network operators.
However, forwarding entries or static configuration for a flow at
each FWD is required. For example, if there are 10,000 flows to be
handled at a CF/FWD, the routing 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 Service Chain
per user (which means that individual users have their own policies),
because some large carriers have over a million users and even more
flows. Another concern is the traffic increase in the control plane
because route setting is required for each flow. Moreover, it may be
hard to use this method if some service functions 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 routing tables. The results of
the above analysis suggest that this method may be suitable for
networks with a limited number of flows.
4.1.2. Analysis of Method 2
In this method, none of the FWDs require any specific routing tables
for Service Chaining, but they require a function to forward packets
based on header information, and to remove the outermost header from
the received packets. Therefore, the control plane would be simple
because the SC controller would not be required to manage the routing
configuration of FWDs. Also, there are already several technologies
proposed that can be used to achieve this method, such as MPLS.
However, the more the SFs packets traverse, the more headers have to
be added to the packet and this in turn means that the packet size
increases. But packet sizes are restricted by the minimal available
MTU of any link in the network path and exceeding the MTU will
require to fragement the original packet before starting to add more
headers required to the service chaining. This requires more
complexity in processing due to the fragementation, adds a new source
of errors, as fragments of packets can get lost and so the whole
original packet will get discared, and also will cause an increase in
traffic as more packets have to be processed by the network.
Moreover, from a hardware point of view, it might be challenging for
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FWDs or SFs to process packets with variable length headers. In
terms of SF equipments, if fragmented packets need to be reassembled
at every SF, this would be very wasteful of CPU resources, and some
equipment has restricted resources and memory for reassembly. The
results of the above analysis indicate that this method would be
appropriate when the number of SFs in an SC is small, or most packets
are forwarded to a static SP. On the other hand, it may be
unsuitable in cases where there are many SFs in a chain.
4.1.3. Analysis of Method 3
In this method, a tag is defined for each Service Chain. By adopting
single fixed-length tags, this method can prevent an increase in the
amount of traffic in the data plane, and can provide an upper bound
on packet size. (Problems which happen as a result of exceeding MTU
are stated in 4.1.2.) This method also enables FWDs to save
resources when handling flow entries. Therefore, this method has
many advantages in terms of scalability, and it might be appropriate
for use in large-scale networks.
However, this method might require renewal of equipments, or
Operating Systems (OSes) installed in hardware, or softwares, or any
other components to realize the method in network which includes SFs,
if this tag handling is an entirely new mechanism. Furthermore
discussion might be required to deploy such standardized
technologies.
4.2. Analysis of 3.2. Determination of Service Paths
4.2.1. Analysis of Pattern 1
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 determination of the next hop.
Moreover, it is not necessary to maintain the state of each flow.
However, this pattern will impact the flexibility of the SCs, as
adding new SFs to a SC, removing SFs from a SC, or migrating SFs to
other locations requires an update or new creation of a path in the
Service Path. Furthermore, unified management of FWDs and SFs in an
SC domain would be required in setting end-to-end paths. Therefore,
the management system of SPs, for example, a CE, for wide-area
networks that include several segments may be massive and complex.
Figure 7 shows the case in which SPs are established across multiple
datacenters in pattern 1. In Figure 7, a CE manages multiple
datacenters as a single SC domain for establishing SPs across
multiple datacenters.
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In pattern 4.2.1.2 (SF Dedicated Model), the number of flow entries
that FWDs hold can be extremely small, as FWDs hold only static next-
hop information. Also, the CF function would be simple, as the CF
only determines the gateway of each SP. However, because the SF
(instance) is settled for each SP, resource usage would be high if
there were many SPs.
+--------------+
+-----------+Control Entity+----------+
| +--------------+ |
| |
************ | *********************************** | *****************
* | | *
* /------+------\ /------+------\ *
* / Datacenter#1 \ /------\ / Datacenter#2 \ *
* +----+ \ / WAN \ / \ *
* | |======================================================> SP#1 *
* | CF |======================================================> SP#2 *
* : : : *
* | |======================================================> SP#n *
* +----+ / \ / \ / *
* \---------------/ \------/ \-------------/ *
* *
* SC Domain *
**********************************************************************
Fig.7 Establishment of SPs Accross Multiples DCs in Pattern 1
4.2.2. Analysis of Pattern 2
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 load condition of SFs.
Furthermore, 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 into several small areas for WANs, which would
enable a simpler configuration of each CE. Figures 8 shows the case
in which SPs are established across multiple datacenters in pattern
2. In Figure 8, 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.
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However, the (fault) monitoring of the whole SC can get harder as
multiple domains are part of the SC. On the other hand each domain
can perfom its fault management as required (and 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.
Synchronization of
Service Chain info.
+-------------------------------------+
| |
v v
+--------------+ +--------------+
|Control Entity| |Control Entity|
+------+-------+ +------+-------+
| |
************ | ************* ********** | **************
* | * * | *
* /------+------\ * * /------+------\ *
* / Datacenter#1 \ * /------\ * / Datacenter#2 \ *
* +----+ +-----+ * / WAN \ * +-----+ | *
* | |==========>| | * | | * | |===========> SP#1*
* | CF |==========>| FWD |===============>| FWD |===========> SP#2*
* : : : * | | * : : : *
* | |==========>| | * \ / * | |===========> SP#n*
* +----+ +-----+ * \------/ * +-----+ / *
* \---------------/ * * \-------------/ *
* * * *
* SC Domain#1 * * SC Domain#2 *
**************************** ***************************
Fig.8 Establishment of SPs Accross Multiples DCs in pattern 2
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.
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4.3.1. Example A: Datacenter Network
The conditions of network A are as follows:
1. The network is used for several business offices as a single DC.
2. Service Chain varies per office (not per user).
3. The number of SF included in for each Service Chain is few. (e.g.
within 5.)
4. SF (instance) cost is not so high.
5. MTU should not be restricted.
6. Service Chains do not fork paths through end-to-end. (As
monitoring, or controlling will be harder, some operators may not
want to change paths after packets got into a service chain.)
On the basis of conditions 4 and 6, Pattern 1 (SF Dedicated Model)
would be selected. In this case, any method would be applicable.
(Even if method 2 is selected, only one header that shows the gateway
to the specific SC is stacked on packets. This does not restrict the
MTU.)
4.3.2. Example B: Current Mobile Carrier Network
The conditions of network B are as follows:
1. The network handles millions of users.
2. Service Chain (SF set and order) is predefined and limited.
3. The number of SF, included in for each Service Chain, is few.
(e.g. within 5.)
4. The user chooses or the provider can choose for the user a
predefined Service Chain to adopt to their traffic.
5. SFs are located in (S)Gi-LAN.(Term referred to draft-ietf-sfc-use-
case-mobility-01)
6. Service Chains do not require to fork paths through end-to-end.
On the basis of conditions 1, 2, and 5, Pattern 1 (SF Shared Model)
would be selected because the architecture would be simple.
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On the basis of conditions 3 and 4, method 1 (unless the
configuration or forwarding table does not increase explosively) or 3
would be applicable.
4.3.3. Example C: Fixed Mobile Convergence Network
Conditions of the network A is as follows:
1. The network handles millions of users.
2. The user chooses or the provider can choose for the user multiple
SFs to adopt to their traffic.
3. Many SFs (e.g. 5 or more,) are included in for each Service Chain.
4. SFs are located in multiple DCs.(e.g. Some delay sensitive SFs,
or SFs which should be placed near users' locations are installed
in DCs located locally, and added-value SFs are installed in DCs
located centrally.)
5. There are some expansive SFs (instance) that should be shared by
several SPs.
6. Service Chains may be forked according to the process of SF.
On the basis of conditions 1, 2, 3, 4, and 5, Method 3 would be
applicable in terms of scalability. Pattern 2 should be selected
based on conditions 1 and 6. Although the operation would be
complex, there may be a case in which some carriers set multiple DCs
and separate SC domains according to their network or service policy.
The use case and architecture pattern is introduced in draft-ietf-
sfc-dc-use-cases-01.
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):
Hiroshi Dempo
NEC
David Dolson
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Sandvine
Ron Parker
Affirmed Networks
Paul Quinn
Cisco Systems
Martin Stiemerling
NEC
7. IANA Considerations
This memo includes no request to IANA.
8. References
[I-D.ietf-sfc-architecture]
Halpern, J. and C. Pignataro, "Service Function Chaining
(SFC) Architecture", draft-ietf-sfc-architecture-02 (work
in progress), September 2014.
[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-01 (work in
progress), July 2014.
[I-D.ietf-sfc-problem-statement]
Quinn, P. and T. Nadeau, "Service Function Chaining
Problem Statement", draft-ietf-sfc-problem-statement-10
(work in progress), August 2014.
[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-01 (work in
progress), July 2014.
[I-D.quinn-sfc-nsh]
Quinn, P., Guichard, J., Fernando, R., Surendra, S.,
Smith, M., Yadav, N., Agarwal, P., Manur, R., Chauhan, A.,
Elzur, U., Garg, P., McConnell, B., and C. Wright,
"Network Service Header", draft-quinn-sfc-nsh-03 (work in
progress), July 2014.
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[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022, January
2001.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, June 2011.
Authors' Addresses
Shunsuke Homma
NTT, Corp.
3-9-11, Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Email: homma.shunsuke@lab.ntt.co.jp
Kengo Naito
NTT, Corp.
3-9-11, Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Email: naito.kengo@lab.ntt.co.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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