Service Function Chaining Qi Xu
Internet Draft Huachun Zhou
Intended status: Standards Track Taixin Li
Expires: December 12, 2016 Guanglei Li
Guanwen Li
Beijing Jiaotong University
June 11, 2016
A Coordinated Forwarding Method for Hierarchical SFC
draft-xu-sfc-coordinated-forwarding-00.txt
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Abstract
Hierarchical SFC is a network architecture for implementing SFC the
chain with an ordered set of service functions which could be
deployed in multiple geographically dispersed networks. How to
forward traffic between networks in Hierarchical SFC is what the
draft wants to present.
This document proposes a mapping-based forwarding method with
coordinated orchestration by the translation of H-SFC and I-SFC to
forward traffic between networks in Hierarchical SFC.
Table of Contents
1. Introduction ................................................ 2
1.1. Assumptions ............................................ 3
1.2. Requirements Language................................... 3
2. Terminology ................................................. 3
3. Coordinated forwardind....................................... 3
3.1. Coordinated Control Planes.............................. 4
3.2. Mapping-based forwarding method......................... 5
4. Metadata Consideration....................................... 7
5. Security Considerations...................................... 7
6. IANA Considerations ......................................... 7
7. References .................................................. 7
7.1. Normative References.................................... 7
7.2. Informative References.................................. 7
Authors' Addresses ............................................. 9
1. Introduction
Hierarchical SFC is a network architecture for implementing SFC the
chain with an ordered set of service functions which could be
deployed in multiple geographically dispersed networks. Hierarchical
SFC is described in detail in [I.D. dolson-sfc-hierarchical] and
[I.D.ao-sfc-for-dc-interconnect], and is not repeated here.
Because of hierarchical SFC supports service decomposition which
means a SF chained by a SFC can be decomposed into several more
refined SFs, a SF might be logical wherever it is deployed. So it is
necessary to check the availability of SFs especially those logical
SFs in the procedure of orchestration.
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This document proposes that adding an interface in the SFC control
plane for coordination between different SFC control planes of
separate domains to achieve hierarchical service decompositions and
describes a mapping-based forwarding method between multiple SFC
domains for Hierarchical SFC in detail.
1.1. Assumptions
The following assumptions are made:
o A Hierarchical SFC-enabled network has multiple level network
domains. Each domain has their own control plane and data plane.
o Control planes of different domain can work coordinately, but
they are independent or non-transparent to each other. For
example Top-Level network domain just uses logical SFs, but don't
care how to construct a corresponding SFC for these logical SFs
in Lower-Level network domains.
1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Terminology
The reader should be familiar with the terms contained in [RFC7665],
[I-D.ietf-sfc-control-plane], [I-D.dolson-sfc-hierarchical] and [I-
D.ao-sfc-for-dc-interconnect].
H-SFC: The SFC in the Top-Level network domain.
I-SFC: The SFC in the Lower-Level network domain.
3. Coordinated forwardind
When receiving a service request, the control plane should decide a
SFC for it, select appropriate SFs of the SFC and make a SFP for the
SFC. Furthermore, a classification policy which binds the flow with
the request to a given SFC should be told to classifiers so that the
flow can pass through relevant SFs along the SFP.
But in hierarchical SFC, SFs might be logical which means it can be
decomposed to several less abstract, more refined SFs. Besides,
logical SFs always represent SFCs in SFC-enabled subdomains. So, how
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to guarantee the availability of logical SFs and forward SFC traffic
among multiple SFC-enabled domains is an important problem.
What follows in this document is going to describe how to solve
aforementioned problem.
3.1. Coordinated Control Planes
+----------------------+ C5
| SFC Control Plane +---->
| |
+---+----+----+----+---+
| | | |
| | | v
| | v C4
| v C3
v C2
C1
Figure 1: Interfaces of SFC Control Plane
[I-D.ietf-sfc-control-plane] presents a reference architecture of
the SFC control plane, including 4 kinds of interfaces between the
SFC control plane and various SFC data plane elements.
But in hierarchical SFC that SFs are distributed over multiple SFC-
enabled domains that the SFC needs to pass through, it is important
to provide an interface for coordination among those control planes
of separate domains.
Figure 1 shows the interface reference points of the SFC control
plane architecture. C1 is the interface between SFC Control Plane
and SFC Classifier;C2 is the interface between SFC Control Plane and
SFF;C3 is the interface between SFC Control Plane and SFC-aware
SFs;C4 is the interface between SFC Control Plane and SFC Proxy;C5
this document proposes is the interface between SFC Control Planes.
At the Top-level, the SFs that compose an SFC might be logical which
means they are actually SFCs composed by more refined SFs in the
Lower-Levels. To setup these logical SFs, it needs coordinated
orchestration between the control planes of the Top-level and the
Lower-levels. During the orchestration for the logical SF of a SFC
in the Top-Level, the control plane of the Top-Level should send an
instruction to the control plane of the corresponding Lower-Level.
When the latter receives this instruction that it is likely that the
Top-level receives a service request from users, Lower-Level would
construct or assign an I-SFC for this "service request" which is
from the Top-Level, and make a classification rules for classifier
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in the IBN who connects the Top-Level with the Lowe-Level to match
the received H-SFC with the corresponding I-SFC.
3.2. Mapping-based forwarding method
This section shows an example of the processing of traffic
forwarding between network domains. It is assumed that all logical
SFs of H-SFC have been constructed by Lower-Level subdomains and
relevant IBNs have known the classification rules.
+---------------+
| SF#2 |
+-----^---+-----+
| |
| |
| |
+---------+ +---------+ +--+---v--+ +---------+
| CF #1 +----> SFF #1 +-------> SFF #2 +-------> SFF #3 +---->
+---------+ +--+---^--+ +---------+ +--+---^--+
| | | |
| | +-----v---+-----+
+----------------------------+ | complex SF#3 |
| | | | +---------------+
| +-----v---+-----+ |
| | complex SF#1 | |
| +-----+------^--+ | Top-Level
| | | |
+------------------------------------------------------------------+
| | | |
+------------------------------------------------------------------+
| | | |
| +----------------+ | Lower-Level
| | | | | |
| | | +--+-----+ | |
| | | | SFF <----------------------------------+
| | | +--------+ | | |
| | | | | |
| | | | | |
| | | +--------+ | | +--------+ +--------+ |
| | +---> CF +-------->SFF #1.1+---->SFF #1.2+--+
| | +--------+ | | +--+--^--+ +--+--^--+
| +----------------+ | | | | |
| IBN | | | | |
| | +--v--+--+ +--v--+--+
| | | SF#1.1 | | SF#1.2 |
+----------------------------+ +--------+ +--------+
Figure 2: An example of Hierarchical SFC
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Below is the working process:
1. The IBN receives an H-SFC encapsulated packet from a Top-Level
network domain.
2. To select an appropriate I-SFC encapsulation for the packet
within the Lower-Level network domain, reclassification would be
performed by classifier module of the IBN according to H-SFC
header information and classification rules, as the example of
figure 3. Extraordinarily, the last SI of I-SFC MUST be the IBN
so that the flow can go back to the H-SFC through the IBN when
the I-SFC is over.
+--------+--------+ +----------+----------+
| H-SFC | SF | | I-SFC | SF |
+-----------------+ +-----------> +---------------------+
| 8/2 | FW | | 6/3 | EdgeFW |
+--------+--------+ + +---------------------+
| | 6/2 | AppFW |
| +---------------------+
| | 6/1 | IBN |
+-----------> +----------+----------+
Figure 3: An example of Reclassification
3. The IBN stores the entire original H-SFC header information, as
well as the mapping relation of H-SFC and I-SFC.
4. After reclassification, original H-SFC header of the packet would
be replaced by the I-SFC header so that the packet could traverse
the Lower-Level domain along the SFP of I-SFC.
5. When the I-SFC encapsulated packets return to the IBN at the end,
the SFF module of the IBN would parse the I-SFC header of the
packets to check whether the I-SFC is over.
6. For returning traffic from Lower-Level to Top-Level, IBN MUST
look up the mapping relation to remove the I-SFC header and
retrieve the original H-SFC header for the packets.
7. Before the packets with the original H-SFC header return to the
Top-level domain, IBN MUST decrement the value of SI of the H-SFC
header. If necessary, IBN would modify or consume or produce
metadata according to the policy of the complex SF.
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4. Metadata Consideration
Because the IBN is regarded as a Service Function to the Top-level
domain, it should provide the ability to handle the metadata in the
NSH header if necessary.
For example, it is common that checking the liveness of the service
function of a service function path before the traffic selected by a
Classifier traverse the network along a SFC which has been describe
in [I-D.penno-sfc-trace-03]. Therefore the IBN must be able to add
its identifying information at the end of the existing NSH headers
as a Service Function.
5. Security Considerations
TBD.
6. IANA Considerations
TBD.
7. References
7.1. Normative References
[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>.
7.2. Informative References
[I-D.dolson-sfc-hierarchical]
Dolson, D., Homma, S., Lopez, D., Boucadair, M., D.Liu,
and Ao, T., "Hierarchical Service Function Chaining",
draft-dolson-sfc-hierarchical-05 (work in progress), March
2016.
[I-D.ao-sfc-for-dc-interconnect]
Ao, T. and W. Bo, "Hierarchical SFC for DC
Interconnection", draft-ao-sfc-for-dc-interconnect-01(work
in progress), October 2015.
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[I-D.ietf-sfc-dc-use-cases]
Komma, 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-control-plane]
Boucadair, M., Ed., "Service Function Chaining (SFC)
Control Plane Components & Requirements", draft-ietf-sfc-
control-plane-06 (work in progress), May 2016.
[I-D.unify-sfc-control-plane-exp]
Szabo, R., Sonkoly, B., "A Multi-Domain Multi-Technology
SFC Control Plane Experiment: A UNIFYed", draft-unify-sfc-
control-plane-exp-00 (work in progress), March 2016.
[1] Sahhaf, Sahel, et al. "Network service chaining with
optimized network function embedding supporting service
decompositions." Computer Networks (2015): 492-505.
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Authors' Addresses
Qi Xu
Beijing Jiaotong University
Beijing 100044 P.R. China
Email: 15111046@bjtu.edu.cn
Huachun Zhou
Beijing Jiaotong University
Beijing 100044 P.R. China
Email: hchzhou@bjtu.edu.cn
Taixin Li
Beijing Jiaotong University
Beijing 100044 P.R. China
Email: 14111040@bjtu.edu.cn
Guanglei Li
Beijing Jiaotong University
Beijing 100044 P.R. China
Email: 15111035@bjtu.edu.cn
Guanwen Li
Beijing Jiaotong University
Beijing 100044 P.R. China
Email: 14120079@bjtu.edu.cn
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