SFC WG Ting. Ao
Internet-Draft Bo. Wu
Intended status: Standards Track ZTE Corporation
Expires: November 30, 2015 May 29, 2015
Hierarchical SFC for DC Interconnection
draft-ao-sfc-for-dc-interconnect-00.txt
Abstract
Sometimes some SFs of a SFC are provided by several DC networks.
That means a SFC may cross several SFs in different DC network. How
to establish such SFC that is across several DCs is what we want to
state. In this document, a hierarchical SFC method is proposed. It
will cover data plane, control plane for such hierarchical SFC. And
it includes requirements of the SFC Gateway for every DC network that
provide SF for SFC.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Architecture of Hierarchical SFC . . . . . . . . . . . . . . 3
3.1. SFC-GW . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Classifier for Inter-SF . . . . . . . . . . . . . . . . . 5
4. Encapsulation . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Overlap SFC encapsulation . . . . . . . . . . . . . . . . 6
4.2. Metadata SFC encapsulation . . . . . . . . . . . . . . . 6
4.3. Exchange SFC encapsulation . . . . . . . . . . . . . . . 7
5. Coordination . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. Information References . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Service Function Chain (SFC) is the chain with a series of ordered
Service Functions(SF). These SFs are distributed in a DC network or
some DC networks. So it's common that a SFC is across several DC
networks, which incurs the problem of DC network interconnection.
Every part of the SFC in one DC network is a SFC within DC network.
We call such SFC to be hierarchical SFC. And the part of such SFC
within a DC network is called to be Inter-SF. Inter-SF may contain
one or more SFs that are within one DC network, but is a logical SF
from the view of the hierarchical SFC.
This document is going to describe the architecture for such
scenario. And data plane and control plane will be provided to
specify how the hierarchical SFC works. Meantime, some concepts are
proposed.
2. Terminology
SFC(Service Function Chain): An ordered set of some abstract SFs.
H-SFC(Hierarchical SFC): A SFC that transfers one or more Data center
networks. Every Datacenter network provide a inter-SF for H-SFC.
Inter-SF: A logical SF that is provided by a SFC in Datacenter
network. For H-SFC, the Inter-SF in one Datacenter network is
regarded as a SF on the path of this H-SFC.
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I-SFC( Internal-SFC): A Service Function Chain within the Datacenter
network which is corresponding to the Inter-SF in H-SFC.
SFC-GW: A gateway for SFC in Datacenter network which is used to
interconnect with H-SFC.
3. Architecture of Hierarchical SFC
Hierarchical SFC is composed of an ordered of SFs or Inter-SFs.
Inter-SF is a logic SF that is composed of an ordered of SFs which
form a SFC in DC network. We can connect every SFC of every
Datacenter network as a whole H-SFC.
For more details about H-SFC, please see Figure 1. To setup such
H-SFC, we need to:
1) To deteremin what kind of service the Inter-SF should provide has
been determined by the Orchestration;
2) To establish the corresponding SFC in the Datacenter network of
the Inter-SF has been established by the controller of the Datacenter
network;
3) Inter-SF also has its SFID in H-SFC;
4) Inter-SF as next hop of the H-SFC also has its locator, which may
be the address of the SFC-GW. This locator information has been
exchanged with Controller1.
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+-------------+
| Controller1 |<-------------------------------------+
+-------------+ |
^ |
| |
+--------------+--------------+-----+----+-------------------+ |
| | | | |
| | .........|......... | |
| +--------------+ . +--------------+ . +--------------+ v
| | SFF1 | . | SFF2 | . | SFF3 | +-----------------+
| +--------------+ . +--------------+ . +--------------+ | |
| | . | . | | Orchestration |
| | . | . | | |
v v . v . v +-----------------+
+--------+ +-------------+ . +-------------+ . +-------------+ ^
--->| CF1 |---> | Inter-SF#1 |---.--> | Inter-SF#2 |--.-->| Inter-SF#3 |-----> |
+--------+ +-------------+ . +-------------+ . +-------------+ |
. .................. |
|| |
|| |
|| |
\/ |
(-------------------) |
/ +-------------+ \ |
/ | Controller2 |<---\-------------------------------+
/ +-------------+ \
/ ^ )--------------------\
/--------( | \
/ +------------+----------------+---------------+ \
/ | | | \
/ v | | \
/ +------------------------------+ v v \
/ | +----------+ +--------+ | +---------+ +---------+ \
<=============>| | SFC-GW |---->| CF2 |-|----->| SN#21 |---->| SN#31 | \
| | +----------+ +--------+ | +---------+ +---------+ \
| +-------^----------------------+ | |
| | | |
| +--------------------------------------------------+ |
| DC Network |
(--------------------------------------------------------------------------)
Figure 1 H-SFC architecture
In the Figure 1, the Inter-SF#1, Inter-SF#2, Inter-SF#3 which is
provided by a separate Datacenter network are an ordered set of a
Hierarchical SFC. For this H-SFC, it's a logical SF. But for this
datacenter network, it actually is a SFC within the datacenter
network.
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CF1 classifies the traffic and assign it a H-SFC. The traffic
traverses along the path according to this H-SFC. Whenever the
traffic enters into Inter-SF#n, it actually enters into the
corresponding Datacenter network through SFC-GW to begin its SFC.
The setup of this SFC in the datacenter is invisible to H-SFC. The
path of the SFC in the datacenter network is also invisible to H-SFC.
3.1. SFC-GW
SFC-GW is the component through which Inter-SF#n communicate with
H-SFC. For H-SFC, the SFC-GW can be considered as a SFF for the
corresponding Inter-SF#n,see Figure 2. And the SFC-GW's locator is
regard as the next hope address of the HSFC. Traffic enters into
Inter-SF#n arrives the SFC-GW firstly. And then the SFC-GW forwards
the traffic to the Classifier in Datacenter network.
When the traffic finishes this SFC in the Datacenter network, it
should be forwarded back to SFC-GW, and then be forwarded to next SF
or Inter-SF by the SFC-GW.
+------------------------------+ +---------+
| SFC-GW | =======>| SFF |
+------------------------------+ +---------+
| |
| |
v |
................................... v
. +------+ +------+ +------+ . +---------+
. | CF |-->| SF1 |-->| SF2 | . ========>| SF |
. +------+ +------+ +------+ . +---------+
................................... ^
^ *
* *
* *
ISFC view HSFC view
Figure 2 View of the SFC-GW
3.2. Classifier for Inter-SF
Classifier for Inter-SF receives the traffic from SFC-GW. For the
traffic, the Classifier classifies the traffic and maps the traffic
into corresponding SFC in the Datacenter network according to the
H-SFC header information. The Classifier assigns the traffic the SFC
header and the traffic is forwarded alone the SFP specified by the
SFC header.
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4. Encapsulation
As description in section 3, SFC in Datacenter network is invisible
to H-SFC. So it's not feasible to use the forwarding method of SFC
that is in one Datacenter network. We need to assign a new SFC
header for the specific SFC in the Datacenter network.
Here is the analysis for the methods to handle the SFC in the
Datacenter network.
4.1. Overlap SFC encapsulation
When the packets with H-SFC header arrives the Classifier in the
Datacenter network, this Classifier would assign a new I-SFC header
based on the H-SFC header. An example is showed like the following
format, Figure 3.
+------------------+
| Overlay Header |
+------------------+
| I-SFC Header |
+------------------+
| H-SFC Header |
+------------------+
| Original Packet |
+------------------+
Figure 3 View of the SFC-GW
The traffic with the above 2 layer-SFC header would be forwarded
according to the I-SFC header in the Datacenter network. H-SFC
header is just preserved in the packets. At the last SFF of the
Service Function Chain of the network, the I-SFC header is removed
from the packet and then the packet is forwarded to the SFC-GW of the
Datacenter network for further forwarding based on the H-SFC header.
With such encapsulation, H-SFC information is carried along the the
whole H-SFC life, so that the last SFF in the Datacenter center of
the I-SFC is not required to be aware of the H-SFC. This forwarding
method eliminates the last SFF's awareness of the H-SFC.
4.2. Metadata SFC encapsulation
In this method, H-SFC header is transferred as a metadata that is
stored in the I-SFC header. And at the last SFF of the I-SFC, the
SFF need to restore metadata information into H-SFC header, then pass
such traffic to SFC-GW.
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This method requires that the last SFF must transfer I-SFC header to
H-SFC header before forward the traffic to SFC-GW.
4.3. Exchange SFC encapsulation
In this kind of encapsulation, there is 1 layer SFC header with the
packet all the time. The Classifier in the Datacenter network maps
the H-SFC header to the I-SFC header. And the last SFF of the I-SFC
maps the I-SFC header back to H-SFC header.
This method requires the last SFF in Datacenter networknot only map
the I-SFC header back to H-SFC, but also must learn the mapping
information from controller.
5. Coordination
To be added later.
6. Summary
As we discuss above, H-SFC is very useful in the Service Function
Chain across several Datacenter networks so that the SFC is more
scalability. With the overlap SFC encapsulation, we keep the
principle that the two level SFC decouple as possible as it can. And
we can use the existing SFC in Datacenter to be a Inter-SF without
modification and with no new requirement for SFF.
7. Security Considerations
To be added later
8. IANA Considerations
N/A
9. Information References
[I-D.ietf-sfc-architecture]
Halpern, J. and C. Pignataro, "Service Function Chaining
(SFC) Architecture", draft-ietf-sfc-architecture-08 (work
in progress), May 2015.
[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-02 (work in
progress), January 2015.
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[I-D.ietf-sfc-nsh]
Quinn, P. and U. Elzur, "Network Service Header", draft-
ietf-sfc-nsh-00 (work in progress), March 2015.
[RFC7498] Quinn, P. and T. Nadeau, "Problem Statement for Service
Function Chaining", RFC 7498, April 2015.
Authors' Addresses
Ting Ao
ZTE Corporation
No.50, Ruanjian Road
Nanjing 210012
China
Phone: +86 25 88016576
Email: ao.ting@zte.com.cn
Bo Wu
ZTE Corporation
No.50, Ruanjian Road
Nanjing 210012
China
Email: wu.bo@zte.com.cn
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