SFC WG T. Ao
Internet-Draft ZTE Corporation
Intended status: Standards Track March 21, 2016
Expires: September 22, 2016
Analysis of the SFC scalability
draft-ao-sfc-scalability-analysis-01.txt
Abstract
SFC as a chain of a set of service function, should be scalable to
meet all kinds of requirements. The scalability of SFC means the SFC
could be elastic to accomodate one or more SFs join the SFC , or
leave the SFC. The document presents four cases for the scalability
of SFC, and analysis the data plane and the control plane to
implement the scalable SFC.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. 4 Use cases for scale-out/scale-in . . . . . . . . . . . . . 3
3.1. Join . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Redundancy . . . . . . . . . . . . . . . . . . . . . . . 3
3.3. By-pass . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.4. Failure or Remove . . . . . . . . . . . . . . . . . . . . 3
4. Data Plane Requirements . . . . . . . . . . . . . . . . . . . 4
5. Control Plane Requirements . . . . . . . . . . . . . . . . . 4
5.1. Centralized CP . . . . . . . . . . . . . . . . . . . . . 4
5.2. Distributed CP . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Information References . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Service Function Chain (SFC) is the chain with a series of ordered
Service Functions(SF). The SFC maybe changed because of load balance
, failure, or other management requirement. We call it SFC's
scalability. The SFC being scalable means that the Service Functions
can be added or removed from the path of this SFC. With this
capability, SFC is more flexible and elastic to adapt all kinds of
requirements.
In this document, we will present four use cases on SFC scale-out and
scale-in, and analysis some requirements to support such capability.
2. Terminology
SFC(Service Function Chain): An ordered set of some abstract SFs.
SFC Scale-out: One or more SFs are added into the path of the SFC for
the sake of load balance, protection or other new services
requirement.
SFC Scale-in: One or more SFs are removed from the path of the SFC
for the sake of the SFs are by-passed or the SFs are failed.
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3. 4 Use cases for scale-out/scale-in
3.1. Join
One or more new SFs are required to join the SFC for the traffic that
has been classified to get more Service Functions to process. This
case may be the opposite scenario of the by-pass. At this time, the
SFC is scaled out.
When a SF is needed to join the SFC, control plane need to notify the
previous SFF that a new SF joins the SFC as next SF and its next hop
should be this SF. In this case, SFF forward the traffic not only
according to the SFPID but also according to the metadata in the SFC
header.
3.2. Redundancy
One or more SFs are added into the SFC for Redundancy or Load balance
purpose. This case is different with the first case (section 3.1) in
that the SF is same with one of the SF that is on the path of the
SFC. The new SF is used to protect the current corresponding SF or
to offload the current corresponding SF. This is also a SFC scale-
out case.
In this case, control plane need to notify the previous SFF that a
new SF joins the SFC as a redundancy SF and its next hop should be a
group. To make sure the correctly forwarding, it's required that
there is a Flow id field in the SFC header so that SFF can select a
SF from group according to the Flow id.
3.3. By-pass
This is a SFC scale-in case. This use case has been described in
[draft-ietf-sfc-long-lived-flow-use-cases] and [draft-kumar-sfc-
offloads]. In these two draft, a SF is offload because it is not
necessary to steer the traffic to the SF to improve the performance.
3.4. Failure or Remove
When SF in one SFC is failed out or removed out because of the no
need of load balance or protection, the SFC is scaled in also.
For this case, it's also required that the previous SFF should be
notified that its next hop should be changed to the next SF of the
SF.
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From above SFC scale-out and scale-in cases, we can get some
requirements about control protocol that it should send out a message
about next hop modification to SFF to support such SFC dynamic scale.
4. Data Plane Requirements
For the load balance or protection switch case of the SFC scale
capability, it is required that there is a entropy field in the SFC
head so that SFF can forward the traffic to different load balance SF
according to this entropy field. The entropy field can be named as
Flow ID which should be in SFC header.
This requires Classifier not only classifies the traffic to different
SFPID, but also classifies the traffic with different Flow ID.
5. Control Plane Requirements
Control plane for SFC would be centralized or distributed.
5.1. Centralized CP
Controller is required to:
a) Send a message to SFF that the joined SF connected to set the
correct SFPID and its next hop.
b) Send register message to previous SFF with some information. Such
information not only includes next hop locator, but also includes an
indicator that if the next hop is a new joined SF or the next hop is
a new SF that added into a group. If the indicator is a new joined
SF, it means a new SF will join the SFC. If the indicator is a group
SF, it means a new SF will be added into a group for load balance or
protection.
c) Send de-register message to previous SFF with some information.
Such information not only includes next hop locator, but also
includes an indicator that if the next hop is the next SF because the
current SF is by-passed, or the next hop is the SF that is removed
from a group. If the indicator is the by-passed SF, it means the
current SF is by-passed or is leaving from the SFC. If the indicator
is group SF, it means the current SF will be removed into a
protection group that is for load balance or protection.
5.2. Distributed CP
Distributed CP can be used in Plug-and-Play scenario. Distributed CP
requires:
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a) The SF that needs to join the SFC or by-pass from the SFC should
notify the SFF it connects by a message.
b) The SFF should send a register message to the previous SFF with
some information. Such information not only includes next hop
locator, but also includes an indicator that if the next hop is a new
joined SF or the next hop is a new SF that added into a group. If
the indicator is a new joined SF, it means a new SF will join the
SFC. If the indicator is a group SF, it means a new SF will be added
into a group for load balance or protection.
c) The SFF send de-register message to previous SFF with some
information. Such information not only includes next hop locator,
but also includes an indicator that if the next hop is the next SF
because the current SF is by-passed, or the next hop is the SF that
is removed from a group. If the indicator is the by-passed SF, it
means the current SF is by-passed or is leaving from the SFC. If the
indicator is group SF, it means the current SF will be removed into a
protection group that is for load balance or protection.
6. Security Considerations
For the scalability of the SFC, security is very important to be
considered. Before allow the SF to join to the SFC, it is required
to make sure the SF's security first.
7. IANA Considerations
N/A
8. Information References
[I-D.ietf-sfc-nsh]
Quinn, P. and U. Elzur, "Network Service Header", draft-
ietf-sfc-nsh-02 (work in progress), January 2016.
[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>.
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Author's Address
Ting Ao
ZTE Corporation
No.889, BiBo Road
Shanghai 201203
China
Phone: +86 21 68897642
Email: ao.ting@zte.com.cn
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