A Framework for Constructing Service Function Chaining Systems Based on Segment Routing
draft-li-spring-sr-sfc-control-plane-framework-00
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| Authors | Cheng Li , Zhenbin Li | ||
| Last updated | 2019-06-25 | ||
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draft-li-spring-sr-sfc-control-plane-framework-00
SPRING Working Group C. Li
Internet-Draft Z. Li
Intended status: Informational Huawei Technologies
Expires: December 28, 2019 June 26, 2019
A Framework for Constructing Service Function Chaining Systems Based on
Segment Routing
draft-li-spring-sr-sfc-control-plane-framework-00
Abstract
Segment Routing (SR) allows for a flexible definition of end-to-end
paths by encoding paths as sequences of topological sub-paths, called
"segments". Segment routing architecture can be implemented over an
MPLS data plane as well as an IPv6 data plane.
Service Function Chaining (SFC) provides support for the creation of
composite services that consist of an ordered set of Service
Functions (SF) that are to be applied to packets and/or frames
selected as a result of classification.
SFC can be implemented based on several technologies, such as Network
Service Header (NSH) and SR. This document describes a framework for
constructing SFC based on Segment Routing. The document reviews the
control plane solutions for route distribution of service function
instance and service function path,and steering packets into a
service function chain.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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 December 28, 2019.
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Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview of SR Based SFC Control Plane . . . . . . . . . . . 4
3. Stateless SR Based SFC . . . . . . . . . . . . . . . . . . . 6
3.1. Service Function Instance Route Distribution . . . . . . 7
3.2. Service Function Path Route Distribution . . . . . . . . 7
3.3. Steer Packets into SFC . . . . . . . . . . . . . . . . . 8
4. Stateful SR Based SFC . . . . . . . . . . . . . . . . . . . . 8
4.1. Service Function Route Distribution . . . . . . . . . . . 8
4.2. Service Function Path Route Distribution . . . . . . . . 8
4.3. Steer Packets into SFC . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
Segment routing (SR) [RFC8402]is a source routing paradigm that
explicitly indicates the forwarding path for packets at the ingress
node by inserting an ordered list of instructions, called segments.
When segment routing is deployed on MPLS dataplane, it is called SR-
MPLS [I-D.ietf-spring-segment-routing-mpls]. When segment routing is
deployed on IPv6 dataplane, it is called SRv6
[I-D.ietf-6man-segment-routing-header].
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Service Function Chaining (SFC) [RFC7665] provides an architecture
that supports the creation of composite service instances that
consist of an ordered set of Service Functions (SF) that are to be
applied to packets and/or frames selected as a result of
classification.
SFC can be implemented based on Network Service Header [RFC8300]. In
NSH-based SFC, per-SFC state, such as a mapping between Service Path
ID (SPI) and Service Index (SI) to next-hop forwarding, needs to be
maintained on nodes along the service function path, and it can
therefore be termed as "stateful SFC".
[I-D.ietf-bess-nsh-bgp-control-plane] defines the use of BGP as a
control plane for networks that support Service Function Chaining
(SFC) based on NSH and MPLS. The document introduces a new BGP
address family called the SFC AFI/SAFI with two route types: Service
Function Instance Route (SFIR) and Service Function Path Route
(SFPR). A NSH or MPLS based SFC can be constructed based on the
information of SFIR and SFPR.
SFC can also be instantiated based on SR. In SR, the forwarding path
is explicitly encoded into the packets on the SR source node. In SR-
based SFC, an SFC can be represented by a SID list explicitly
indicated by the source SR node. The SID in SID list may need to be
associated with service information in order to indicate network
service, such as Deep Packet Inspection (DPI). Therefore, no per-SFC
state needs to be maintained along with the service function path,
and it can therefore be termed "stateless SFC".
In order to construct SR-based SFC, several mechanisms are proposed,
including the mechanisms of Service Function Instance Route(SFIR) and
Service Function Path Route(SFPR) distribution, as well as the
mechanism of steering packets into an SFP. This document reviews
these solutions to describe a framework for the construction of a
service function chaining system based on Segment Routing.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.2. Terminology
MPLS: Multiprotocol Label Switching.
SID: Segment Identifier.
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SR: Segment Routing.
SR-MPLS: Segment Routing with MPLS data plane.
SRH: Segment Routing Header.
SFIR: Service Function Instance Route
SFPR: Service Function Path Route
Further, this document makes use of the terms defined in [RFC7665]
and [I-D.xuclad-spring-sr-service-programming].
2. Overview of SR Based SFC Control Plane
As per [RFC7665], the architecture of SFC consists of classifiers,
Service Function Forwarders (SFFs), Service Functions (SFs) and SFC
proxies, see Figure 1.
+-----+ +-----+ +-----+
| | | SFC | | |
| SF1 | |Proxy|---| SF2 |
+-----+ +-----+ +-----+
| |
+--------------+ | |
| Service | SFC +------+ +------+
|Classification| Encapsulation | SFF1 | | SFF2 |
---->| Function |+---------------->| |--------| |-------->
| | | | | |
+--------------+ +------+ +------+
SFC-enabled Domain
Figure 1. SFC Architecture
In order to construct a service function chain, SFIR and SFPR should
be distributed to classifiers and SFFs. Also, the rules of steering
packets into specific service function paths should be configured at
the classifier. [I-D.ietf-bess-nsh-bgp-control-plane].
In SR, a source node can explicitly indicate the forwarding path for
packets by inserting an ordered list of instructions. These packets
steering policies, known as SR policy, can be installed by a central
controller via BGP [I-D.ietf-idr-segment-routing-te-policy] or other
mechanisms.
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When SFC is constructed based on SR, SFPR and pakcet steering rules
can be installed by SR policy at the ingress node, which plays the
role of classifier in the SFC architecture. In other words, SFPR
does not need to be distributed to all the nodes along the service
function path. The architecture of SR based SFC is illustrated in
Figure 2.
+-----+ +-----+ +-----+ +-----+
| | | | | SR | | |
|SR-C | | SF1 | |Proxy|---| SF2 |
+-----+ +-----+ +-----+ +-----+
| | |
| | |
+--------------+ +------+ +------+
| | SFC Encap/SR | SFF1/| | SFF2/|
---->|CF/SR ingress |+---------------->| SR |--------| SR |-------->
| | | | | |
+--------------+ +------+ +------+
SFC-enabled Domain
Figure 2. SR based SFC architecture.
o CF/SR ingress: an SR ingress node plays the role of Classifier in
the SFC architecture, and it connects to an SR controller, where
the SR policies originate.
o SR-C: SR Controller (SR-C) is connected to the SR ingress node,
and may be attached to any node in the network. SR-C is capable
of discovering topology, and calculating constrained paths for
service function chains.
o SFF/SR nodes: the SFF component in SFC architecture, which enables
SR to steer packets to SFs.
o SFn: Service Functions, can be SR-aware or SR-unaware. If an SF
is SR-unaware then SR proxy is needed.
o SR proxy: A proxy between SR nodes/SFF and SR-unaware SF.
There are two solutions to encode SFC in the SR data plane.
[I-D.xuclad-spring-sr-service-programming] defines data plane
functionality required to implement service segments and achieve
service programming in SR-enabled MPLS and IP networks. It can be
termed "Stateless SFC" since no per-SFC state is maintained on the SR
nodes along the service function path.
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The second solution can be termed "Stateful
SFC"[I-D.guichard-spring-nsh-sr], since it still maintains per-SFC
state on nodes. [I-D.guichard-spring-nsh-sr]describes two modes:
o NSH-based SFC with SR-based transport tunnel: SR is used as
transport tunnel to route packets between classifier and SFF or
SFFs. Service plane routing relies on NSH.
o SR-based SFC with Integrated NSH Service Plane: The Service
Function Path is encoded within the SR segment-list, while the NSH
only maintains the service plane context information, which will
be used at NSH-aware SFs, and at SFFs for caching of SR segment-
lists.
In order to support these data plane encodings, control plane
mechanisms are required. The existing control plane mechanisms are
shown in table 1.
+------------------------------------------------------------+
| SR based SFC | SFIR | SFPR | Steering policy|
+-------------------+-----------+-----------+----------------+
| | BGP | BGP | BGP |
|Stateless | BGP-LS | PCEP | PCEP |
| | IGP | | |
+-------------------+-----------+-----------+----------------+
|NSH-based SFC | BGP | BGP | BGP |
|with SR-based | | PCEP | |
|transport tunnel | | | |
| | | | |
| | | | |
+-------------------+-----------+-----------+----------------+
|SR-based SFC | BGP | BGP | BGP |
|with Integrated | BGP-LS | PCEP | PCEP |
|NSH Service Plane | IGP | | |
| | | | |
+-------------------+-----------+-----------+----------------+
Table 1. SR based SFC Control Plane Solutions
3. Stateless SR Based SFC
As describe in [I-D.xuclad-spring-sr-service-programming], service
instances are associated with a segment, called a service SID. These
service SIDs are leveraged as part of a SID-list to steer packets
through the corresponding services.
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3.1. Service Function Instance Route Distribution
To associate a segment with a service, service information, such as
Service Function Type(SFT), should be included in segment
distribution.
To associate a segment with a service, service information, such as
Service Function Type (SFT), should be included in segment
distribution. [I-D.dawra-idr-bgp-ls-sr-service-segments] specifies
the extensions to BGP-LS for discovery and advertisement of service
segments so as to enable setup of service programming paths using
Segment Routing. [I-D.dawra-idr-bgp-ls-sr-service-segments]extends
SRv6 Node SID TLV [I-D.dawra-idr-bgpls-srv6-ext] and SR-MPLS SID/
Label TLV [I-D.ietf-idr-bgp-ls-segment-routing-ext] to associate the
Service SID Value with Service-related Information using Service
Chaining Sub-TLV. The Service Chaining Sub-TLV contains information
of Service SID value, Function Identifier (Static Proxy, Dynamic
Proxy, Shared Memory Proxy, Masquerading Proxy, SR Aware Service
Etc.), Service Type (DPI, Firewall, Classifier, LB etc.), Traffic
Type (IPv4 OR IPv6 OR Ethernet) and Opaque Data (such as brand and
version, other extra information). This extension works for both SR-
MPLS and SRv6.
[I-D.ietf-bess-nsh-bgp-control-plane] proposes a BGP-based SFC
control plane solution, and it works for SR-MPLS as well. Service
function instance route distribution can use SFIR in SFC AFI/SAFI.
SFPR and steering rules for the classifier can be distributed by SR
policy, which is defined in [I-D.ietf-idr-segment-routing-te-policy].
BGP control plane of SRv6-based SFC still needs to be defined.
IGP extensions are proposed by [I-D.xu-isis-service-function-adv] and
[I-D.xu-ospf-service-function-adv]. . In IS-IS solution, SFFs within
the SFC domain need to advertise each SF they are offering by using a
new sub-TLV of the IS-IS Router CAPABILITY TLV [RFC4971]. This new
sub-TLV is called Service Function sub-TLV, and it can appear
multiple times within a given IS-IS Router CAPABILITY TLV or when
more than one SF needs to be advertised. OSPF extensions are
similar, and use the OSPF Router Information (RI) Opaque LSA
[RFC4970] to carry Service Function sub-TLV.
However, due to IGP flooding issues, IGP extensions are not very
appropriate, and the drafts have expired for a long time.
3.2. Service Function Path Route Distribution
With SR, the SFPR does not need to be distributed to nodes along the
SFP but only to the ingress node. SFPR and steering rules for the
classifier can be distributed by SR policy. The BGP extension is
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defined in [I-D.ietf-idr-segment-routing-te-policy]. The PCEP
extension is defined in [I-D.barth-pce-segment-routing-policy-cp].
3.3. Steer Packets into SFC
In SR, packet steering rules are learned through SR policy. Thus,
there is no need to install other rules in the classifier, which is
the SR source node.
4. Stateful SR Based SFC
"Stateful SFC" [I-D.guichard-spring-nsh-sr]proposes two modes of SR
based SFC:
o NSH-based SFC with SR-based transport tunnel
o SR-based SFC with Integrated NSH Service Plane
4.1. Service Function Route Distribution
For NSH-based SFC with SR-based transport tunnel, service information
is maintained by NSH while SR is only used for transport between
SFFs, so [I-D.ietf-bess-nsh-bgp-control-plane] can be used for this
mode.
To indicate NSH, an SFF label [I-D.ietf-mpls-sfc-encapsulation]
should be inserted as the last label in the label stack in SR-MPLS.
The control plane of SFF is also described in
[I-D.ietf-bess-nsh-bgp-control-plane]. For choosing/configuring SR
as the transport tunnel, BGP route of SFF's BGP Tunnel Encapsulation
Attribute Type should be "SR TE Policy Type"
[I-D.ietf-idr-segment-routing-te-policy]. For SR-based SFC with
Integrated NSH Service Plane, there is no control plane solution as
yet defined.
4.2. Service Function Path Route Distribution
Same as SFIR distribution, SFPR BGP distribution in NSH-based SFC
with SR-based transport tunnel is identical to the mechanism defined
in [I-D.ietf-bess-nsh-bgp-control-plane]. PCEP extension for SFPR
distribution can reuse the NSH based SFC extension defined in
[I-D.wu-pce-traffic-steering-sfc]. For SR-based SFC with Integrated
NSH Service Plane, control plane solution is to be added in other
documents.
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4.3. Steer Packets into SFC
For NSH-based SFC with SR-based transport tunnel, it is the same with
the NSH based SFC. The Classifier is responsible for determining to
which packet flow a packet belongs (usually by inspecting the packet
header), imposing an NSH, and initializing the NSH with the SPI of
the selected SFP and the SI of its first hop
[I-D.ietf-bess-nsh-bgp-control-plane]. For SR-based SFC with
Integrated NSH Service Plane, control plane solution is to be added
in other document.
5. IANA Considerations
This document does not require any IANA actions.
6. Security Considerations
This document does not introduce additional security requirements and
mechanisms.
7. Acknowledgements
TBA
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
8.2. Informative References
[I-D.barth-pce-segment-routing-policy-cp]
Barth, C., Koldychev, M., Sivabalan, S., and C. Li, "PCEP
extension to support Segment Routing Policy Candidate
Paths", draft-barth-pce-segment-routing-policy-cp-02 (work
in progress), March 2019.
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[I-D.dawra-idr-bgp-ls-sr-service-segments]
Dawra, G., Filsfils, C., daniel.bernier@bell.ca, d.,
Uttaro, J., Decraene, B., Elmalky, H., Xu, X., Clad, F.,
and K. Talaulikar, "BGP-LS Advertisement of Segment
Routing Service Segments", draft-dawra-idr-bgp-ls-sr-
service-segments-01 (work in progress), January 2019.
[I-D.dawra-idr-bgpls-srv6-ext]
Dawra, G., Filsfils, C., Talaulikar, K., Chen, M.,
daniel.bernier@bell.ca, d., Uttaro, J., Decraene, B., and
H. Elmalky, "BGP Link State Extensions for SRv6", draft-
dawra-idr-bgpls-srv6-ext-06 (work in progress), March
2019.
[I-D.filsfils-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J.,
daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
Network Programming", draft-filsfils-spring-srv6-network-
programming-07 (work in progress), February 2019.
[I-D.gandhi-spring-udp-pm]
Gandhi, R., Filsfils, C., daniel.voyer@bell.ca, d.,
Salsano, S., Ventre, P., and M. Chen, "UDP Path for In-
band Performance Measurement for Segment Routing
Networks", draft-gandhi-spring-udp-pm-02 (work in
progress), September 2018.
[I-D.guichard-spring-nsh-sr]
Guichard, J., Song, H., Tantsura, J., Halpern, J.,
Henderickx, W., Boucadair, M., and S. Hassan, "NSH and
Segment Routing Integration for Service Function Chaining
(SFC)", draft-guichard-spring-nsh-sr-01 (work in
progress), March 2019.
[I-D.ietf-6man-segment-routing-header]
Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment
Routing Header (SRH)", draft-ietf-6man-segment-routing-
header-21 (work in progress), June 2019.
[I-D.ietf-bess-nsh-bgp-control-plane]
Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L.
Jalil, "BGP Control Plane for NSH SFC", draft-ietf-bess-
nsh-bgp-control-plane-11 (work in progress), May 2019.
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[I-D.ietf-idr-bgp-ls-segment-routing-ext]
Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
and M. Chen, "BGP Link-State extensions for Segment
Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-15
(work in progress), May 2019.
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Jain, D., Mattes, P., Rosen,
E., and S. Lin, "Advertising Segment Routing Policies in
BGP", draft-ietf-idr-segment-routing-te-policy-06 (work in
progress), May 2019.
[I-D.ietf-mpls-sfc-encapsulation]
Malis, A., Bryant, S., Halpern, J., and W. Henderickx,
"MPLS Transport Encapsulation For The SFC NSH", draft-
ietf-mpls-sfc-encapsulation-04 (work in progress), March
2019.
[I-D.ietf-spring-segment-routing-mpls]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-22
(work in progress), May 2019.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
bogdanov@google.com, b., and P. Mattes, "Segment Routing
Policy Architecture", draft-ietf-spring-segment-routing-
policy-03 (work in progress), May 2019.
[I-D.li-idr-sr-policy-path-segment-distribution]
Li, C., Chen, M., Dong, J., and Z. Li, "Segment Routing
Policies for Path Segment and Bidirectional Path", draft-
li-idr-sr-policy-path-segment-distribution-01 (work in
progress), October 2018.
[I-D.li-pce-sr-bidir-path]
Li, C., Chen, M., Cheng, W., Li, Z., Dong, J., Gandhi, R.,
and Q. Xiong, "PCEP Extensions for Associated
Bidirectional Segment Routing (SR) Paths", draft-li-pce-
sr-bidir-path-05 (work in progress), March 2019.
[I-D.li-pce-sr-path-segment]
Li, C., Chen, M., Cheng, W., Dong, J., Li, Z., Gandhi, R.,
and Q. Xiong, "Path Computation Element Communication
Protocol (PCEP) Extension for Path Segment in Segment
Routing (SR)", draft-li-pce-sr-path-segment-05 (work in
progress), March 2019.
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[I-D.wu-pce-traffic-steering-sfc]
Wu, Q., Dhody, D., Boucadair, M., Jacquenet, C., and J.
Tantsura, "PCEP Extensions for Service Function Chaining
(SFC)", draft-wu-pce-traffic-steering-sfc-12 (work in
progress), June 2017.
[I-D.xu-isis-service-function-adv]
Xu, X., Wu, N., Shah, H., and L. Contreras, "Advertising
Service Functions Using IS-IS", draft-xu-isis-service-
function-adv-05 (work in progress), May 2017.
[I-D.xu-ospf-service-function-adv]
Xu, X., Wu, N., Shah, H., and L. Contreras, "Advertising
Service Functions Using OSPF", draft-xu-ospf-service-
function-adv-02 (work in progress), June 2014.
[I-D.xuclad-spring-sr-service-programming]
Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca,
d., Li, C., Decraene, B., Ma, S., Yadlapalli, C.,
Henderickx, W., and S. Salsano, "Service Programming with
Segment Routing", draft-xuclad-spring-sr-service-
programming-02 (work in progress), April 2019.
[RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July
2007, <https://www.rfc-editor.org/info/rfc4970>.
[RFC4971] Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed.,
"Intermediate System to Intermediate System (IS-IS)
Extensions for Advertising Router Information", RFC 4971,
DOI 10.17487/RFC4971, July 2007,
<https://www.rfc-editor.org/info/rfc4971>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/info/rfc7665>.
[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
Li & Li Expires December 28, 2019 [Page 12]
Internet-Draft SR based SFC Control Plane June 2019
Authors' Addresses
Cheng Li
Huawei Technologies
Email: chengli13@huawei.com
Zhenbin Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: lizhenbin@huawei.com
Li & Li Expires December 28, 2019 [Page 13]