Internet DRAFT - draft-fu-sfc-topology
draft-fu-sfc-topology
Internet Engineering Task Force Q. Fu, Ed.
Internet-Draft China Mobile
Intended status: Informational J. Halpern
Expires: April 16, 2016 Ericsson
H. Deng
China Mobile
October 14, 2015
The topology of service function chaining
draft-fu-sfc-topology-01
Abstract
This document proposes a deployment topology of Service Function
Chaining(SFC). The topology is in accordance with the SFC
architecture in [I-D.ietf-sfc-architecture]. Currently, such
architecture only includes architectural concepts, principles, and
components used in the construction of composite services through
deployment of SFCs, without any instruction for the field deployment.
It is still difficult to map from the architecture to a real
deployment of SFC. In this document, we propose this topology which
will give instructions for the field deployments. We further propose
a VCPE usecase of SFC in the transport network, which explains the
details of the deployment topology.
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Topology of SFC in current network . . . . . . . . . . . . . 4
4. vCPE usecase of SFC . . . . . . . . . . . . . . . . . . . . . 5
5. Topology of VCPE Deployment . . . . . . . . . . . . . . . . . 6
6. Details of VCPE deployment in the MPLS-TP Network . . . . . . 8
7. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 9
8. Informative References . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The definition and instantiation of an ordered set of service
functions and subsequent 'steering' of traffic through them is termed
as Service Function Chaining (SFC). The definition of SFC can be
found in [I-D.ietf-sfc-problem-statement]. In
[I-D.ietf-sfc-architecture], an architecture for SFC is proposed,
which includes the basic architectural concepts, principles, and
components used in the construction of SFCs. The high level logical
architecture of SFC is shown in Figure.1, and a detailed architecture
is shown in Figure.2. The definition and functions for the
components in these figures can be found in
[I-D.ietf-sfc-architecture].
o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. +--------------+ +------------------~~~
. | Service | SFC | Service +---+ +---+
. |Classification| Encapsulation | Function |sf1|...|sfn|
+---->| Function |+---------------->| Path +---+ +---+
. +--------------+ +------------------~~~
. SFC-enabled Domain
o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1: High Level Logical Architecture for SFC
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+----------------+ +----------------+
| SFC-aware | | SFC-unaware |
|Service Function| |Service Function|
+-------+--------+ +-------+--------+
| |
SFC Encapsulation No SFC Encapsulation
| SFC |
+---------+ +----------------+ Encapsulation +---------+
|SFC-Aware|-----------------+ \ +------------|SFC Proxy|
| SF | ... ----------+ \ \ / +---------+
+---------+ \ \ \ /
+-------+--------+
| SF Forwarder |
| (SFF) |
+-------+--------+
|
SFC Encapsulation
|
... SFC-enabled Domain ...
|
Network Overlay Transport
|
_,....._
,-' `-.
/ `.
| Network |
`. /
`.__ __,-'
`''''
Figure 2: Detailed Architecture for SFC
However, the architecture proposed in [I-D.ietf-sfc-architecture]
provides little instructions for field deployment of SFC. The
definitons for each component are abstract and are difficult to be
mapped to current network. Therefore, in this document, a topology
of field deployment of SFC is proposed. We further propose a usecase
of vCPE using SFC to fully explain the topology.
2. Terminology
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 [RFC2119].
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3. Topology of SFC in current network
Figure.3 shows the topology of deployment of SFC in the current
network. In general, there are two choices of the deployment of the
SFs. One is to locate in the data centers of Operators. And the
other is to co-locate with the Openrator Gateways(GWs). Such GWs can
be in the aggregate networks or the core networks. These two
deployments both have their advantages. For the first one, the
traffic do not need to travel to the DC and back. For the second
one, it will be easier for us to manage and maintain these SFC
devices.
The Operator GWs should act as SCF(Service Classification Function)
and SFF (Service function Forwarder) in the SFC architecture. This
SFF should be responsible for adding SFC-header to the packets.
Multiple SFFs can be deployed after the GW in large scale use cases,
so as to avoid large volume of traffic returning to the GW
continiously.
The deployment topology of colocating the SCF and SFF will simplify
the classification and forwarding. SFF can add the SFC header to the
traffic flow directly according to the SCF result, and can support
re-classification easily. In the meantime, in some usecases, the SCF
can act as classifier of traffic flows so as to classify the traffic
that need to go through the SFC region and the others that do not
need. In the following VCPE usecase, we can show the colocation of
the GW with the SCF and the SFF can greatly simplify the network
deployment. However, such topology will complicate the Operator GW.
There are other deployments that the SCF and/or the SFF are located
outside the GW, in which case interaction and interface between the
GW, the SCF, and the SFF is required.
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+---------------+
|SFC Unaware SF3|
+------+--------+
|
|
+-----+ +-----+ +----+----+
| SF1 | | SF2 | |SFC Proxy|
+--+--+ +--+--+ +--+------+
| | |
+------+ | +-----+
| | |
+--+-+ +-+--+ +-+--+
|SFF1| |SFF2| |SFF3|
+--+-+ +-+--+ +-+--+
| | |
+-+-----+------+--+
|GW |
+------+ | +-----+ +-----+ | +----------+
| User +-------------+-+ SCF +-+ SFF +-+-----------+ Internet |
+------+ | +-----+ +-----+ | +----------+
+-----------------+
Figure 3: Topology for SFC in the Mobile Networks
4. vCPE usecase of SFC
In this document, we also propose a usecase of Service Function
Chaining (SFC) to realize virtual CPE in the Transport Network. Such
VCPE would provide value-added services, including L4-L7 network
functions to the traditional transport network customers. In order
to flexibly control the traffic flow, we also introduce SDN-
controller (Software Define Network Controller) into the transport
network. The SDN-controller is responsible for directing the traffic
of certain enterprise customer, who has paid for the VCPE services,
to the VCPE servers.
The concept of VCPE is to shift most of the networking and service
functionalities from the customer side to the network side. In this
way, the customer side's equipment, that is the CPE, can be
simplified. The VCPE refers to one or a set of equipments at the
network side to execute the networking and service functionalities
used to be executed at the CPE. In such architecture, the CPE can be
a simple L2 switch, which is only responsible for forwarding packets
to a certain next hop. The VCPE can be realized by a SFC in the
physical network or the virtual network, in which the traffic of each
customer is directed to one or several Service Founctions (SF)
specified by the customer.
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5. Topology of VCPE Deployment
Following the topology given in the previous section, we will propose
a usecase of VCPE deployment in the current Transport network. The
traditional transport network uses static allocation mechanism in
general. In order to provide network connection between different
locations for the enterprise customers, traditional transport network
should allocate dedicated lines between each pair of the locations.
Such architecture is not suitable when the enterprise customers
require LAN access, and moreover, L3-L7 functions among different
locations. Therefore, we introduce Virtual Customer Premise
Equipment (VCPE) into the Transport network. By utilizing SFC, the
VCPE can provide value-added services, such as firewall (FW), NAT,
and etc., to the traditional transport network customers. With the
emergance of the NFV technologies, these services can be one or a set
of VNFs on the VCPE servers. Such architecture provides an agile
mechanism for operators to launch value-added services for the
transport network.
Figure 4 shows the topology of deployment of the usecase for VCPE in
the transport network. The solid lines indicate data traffic flows,
while the dash lines indicate control traffic flows. In this
architecture, the CPEs are located at different branches of the
enterprise customer, and act as L2 forwarding switches. The VCPE is
located at the DC, or co-located with the aggregate GW.
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+-----------------------+
.....+ SDN-Controller +............
: +----+------------------+ :
: : :
: : +------------------------+ :
: : | VCPE | :
: : | +---+ +---+ +---+ | :
: : | |SF1| |SF2| |SF3| | :
: : | +-+-+ +-+-+ +-+-+ | :
: : | | | | | :
: : | +-+--+ +-+--+ +-+--+ | :
: : | |SFF1| |SFF2| |SFF3| | :
: : + +-+--+ +-+--+ +-+--+ | :
: : +---+-------+-------+----+ :
: : +---+ | +---+ :
: : | | | :
+---+------+ : +--+---+---+-+ +----+-----+
| +-+---+ | .......++---+ +---+| | +-+---+ |
| | CPE +--+---------++SCF+--+SFF++-----+--+ CPE | |
| +-----+ | |+---+ +---+| | +-----+ |
|Enterprise| | Aggregate | |Enterprise|
| Branch | | Network GW | | Branch |
+----------+ +------------+ +----------+
Figure 4: Topology of Deployment of VCPE in the transport network
All of the CPEs and the Aggregate Network GW can be controlled by the
SDN-controller. When the enterprise customer selects a set of the
value-added services, the SDN-controller will inform the CPE of the
customer to direct the traffic flow to a certain Aggregate Network GW
connected to the VCPE. The GW acts as SCF and SFF in the SFC region.
It is responsible for classifing the traffic flow of the customers
and adding SFC header. And then it will act as SFF and forward the
traffic tothe other SFFs in the VCPE based on the SFP (Service
Function Path). When finishing the SFP, the GW will remove the SFC
header and forward the traffic flow to the destination CPE. All
these traffic flows are directed under the control of the SDN
controller.
There could be another architecture without the SDN controller, in
which case, the SCF is used to classify which flow shoud go through
the VCPE and enter the SFC region, and which flow should follow the
traditional transport network routine and should be forwarded
directly to the destination CPE.
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6. Details of VCPE deployment in the MPLS-TP Network
Since MPLS-TP is widely used in the current transport network, we are
going to propose this usecase based on the MPLS-TP transport network.
The traditional transport network is only responsible for providing
MPLS-TP connection between each two destinations. No L3-L7 services
can be provided based on it. By introducing VCPE at the aggregate/
core network, and using SFC, multiple L3-L7 services can be provided
using the widely deployed MPLS-TP network.
In the MPLS-TP packet, the PW lable, adhere to the packet by the CPE
device at the customer side of the PTN network, can be used to
classify service type. Such information can be used for Service
Clasification Function. Extra label can also be added into the PW
lable to indicate user/network specifics. Therefore, the SFC can do
the service clasification mapping based on the PW lable in the MPLS-
TP packets. In the meantime, MPLS-TP packets should also be
transfered to L3 packets before entering the Service Function Region,
and should be re-encapsulated to the MPLS-TP packets after leaving
the Service Function Region. According to the deployment topology,
the aggregate GW is acting as both ingress and egress GW of the SFC
region. In this case, the aggregate GW should record the mapping
relationship of the IP address and PW/LSP label of each packet, and
should make sure pf adding the exact same MPLS-TP header to the
packets when they finish the SFP and exit the SFC region, so that the
packet can continue its path in the transport network using the MPLS-
TP header. Therefore, in the MPLT-TP network, the aggregate GW
shoule follow the following steps when an MPLS-TP packet arrives at
the aggregate network.
1) Mapping PW lable to a certain Service Founction Path
2) Recording mapping between IP address and PW/LSP lable, so as to
re-encapsulate the L3 packets with a certain IP address.
3) Transfering MPLS-TP packets to L3 packets by taking off the MPLS-
TP header.
4) Adding SFC header into the L3 packets.
5) Acting as the SFF by forwarding the L3 packets according to the
SFP.
6) Taking off the SFC header when the SFP finishes.
7) Transfering the L3 packets to MPLS-TP packets by adding
corresponding MPLS-TP header according to the recorded mapping.
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8) Forwarding the MPLS-TP Packets to the destination.
For step 2, the following table should be maintained by the GW, in
which SFP indicates Service Function Path.
IP address | LSP label |PW label | SFP
-----------+-----------+---------+------
IP1 | LSP1 | PW1 | SFP1
IP2 | LSP2 | PW2 | SFP2
IP3 | LSP3 | PW3 | SFP3
Figure 5: Mapping table in the GW
This proposed approach can reuse the existing MPLS-TP network, so
that operators can use the same transport network platform to support
both the traditional private line service and value added NFV
services. From the proposed steps, we can see that colocate the SCF
and the SFF with the GW can greatly simplify the whole deployment,
since we don't need to coordinate the mapping info between the SCF
and the GW and the SFF.
7. Conclusion
In this document, a topology of SFC is proposed. Such topology
follows the definition and components of the SFC architecture in
[I-D.ietf-sfc-architecture]. Comparing with the abstract
architecture proposed, such topology provides deployable guidelines
for SFC.
A usecase of VCPE using SFC in the MPLS-TP transport network is
further proposed to detailed the deployment topology. Such usecase
provides an agile mechanism for launching new value-added services in
the transport network. SFC is used in the VCPE to chain different
SFs for different flows according to the customers' specification.
In the meantime, traffic flows are directed with the help of the SDN-
controller according to the customers' specification.
8. Informative References
[I-D.ietf-sfc-architecture]
Halpern, J. and C. Pignataro, "Service Function Chaining
(SFC) Architecture", draft-ietf-sfc-architecture-11 (work
in progress), July 2015.
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[I-D.ietf-sfc-problem-statement]
Quinn, P. and T. Nadeau, "Service Function Chaining
Problem Statement", draft-ietf-sfc-problem-statement-13
(work in progress), February 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
Authors' Addresses
Qiao Fu (editor)
China Mobile
Xuanwumenxi Ave. No.32
Beijing
China
Email: fuqiao1@outlook.com
Joel. Halpern
Ericsson
Email: jmh@joelhalpern.com
Hui Deng
China Mobile
Xuanwumenxi Ave. No.32
Beijing
China
Email: denghui@chinamobile.com
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