Internet DRAFT - draft-xu-sfc-using-mpls-spring
draft-xu-sfc-using-mpls-spring
Network Working Group X. Xu
Internet-Draft Z. Li
Intended status: Standards Track Huawei
Expires: September 8, 2016 H. Shah
Ciena
L. Contreras
Telefonica I+D
March 7, 2016
Service Function Chaining Using MPLS-SPRING
draft-xu-sfc-using-mpls-spring-05
Abstract
Source Packet Routing in Networking (SPRING) WG specifies a special
source routing mechanism. Such source routing mechanism can be
leveraged to realize the service path layer functionality of the
service function chaining (i.e, steering traffic through a particular
service function path) by encoding the service function path or the
service function chain information as the explicit path information.
This document describes how to leverage the MPLS-based source routing
mechanism as developed by the SPRING WG to realize the service path
layer functionality of the service function chaining.
Status of This Memo
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Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Solution Description . . . . . . . . . . . . . . . . . . . . 3
3.1. Encoding SFP Information by an MPLS Label Stack . . . . . 4
3.2. How to Contain Metadata within an MPLS Packet . . . . . . 5
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
When applying a particular Service Function Chain (SFC)
[I-D.ietf-sfc-architecture] to the traffic selected by a service
classifier, the traffic need to be steered through an ordered set of
Service Functions (SF) in the network. This ordered set of SFs in
the network indicates the Service Function Path (SFP) associated with
the above SFC. To steer the selected traffic through an ordered list
of SFs in the network, the traffic need to be attached by the service
classifier with the information about the SFP (i.e., specifying
exactly which Service Function Forwarders (SFFs) and which SFs are to
be visited by traffic), the SFC, or the partially specified SFP which
is in between the former two extremes. Source Packet Routing in
Networking (SPRING) WG specifies a special source routing mechanism
which can be used to steer traffic through an ordered set of routers
(i.e., an explicit path). Such source routing mechanism can be
leveraged to realize the service path layer functionality of the SFC
(i.e., steering traffic through a particular SFP) by encoding the SFP
information as the explicit path information contained in packets.
The source routing mechanism specified by the SPRING WG can be
applied to the MPLS data plane
[I-D.ietf-spring-segment-routing-mpls]. This document describes how
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to leverage the MPLS-based source routing mechanisms to realize the
service path layer functionality of the service function chaining.
Note that this approach is aligned with the Transport Derived SFF
mode as described in Section 4.3.1 of [I-D.ietf-sfc-architecture].
1.1. 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
This memo makes use of the terms defined in
[I-D.ietf-spring-segment-routing] and [I-D.ietf-sfc-architecture].
3. Solution Description
+----------------------------------------------- ----+
| SPRING Networks |
| +---------+ +---------+ |
| | SF1 | | SF2 | |
| +----+----+ +----+----+ |
| | | |
| (1) | (2) | (3) |
+----+-----+ ---> +----+----+ ----> +----+----+ ---> +---+---+
|Classifier+------+ SFF1 +-------+ SFF2 +-------+ D |
+----------+ +---------+ +---------+ +---+---+
| |
+----------------------------------------------------+
Figure 1: Service Function Chaining in SPRING Networks
As shown in Figure 1, assume SFF1 and SFF2 are two MPLS-SPRING-
capable nodes. They are also Service Function Forwarders (SFF) to
which two SFs (i.e., SF1 and SF2) are attached respectively. In
addition, they have allocated and advertised Segment IDs (SID) for
their locally attached SFs. In the MPLS-SPRING context, SIDs are
intercepted as MPLS labels. For example, SFF1 allocates and
advertises an SID (i.e., SID(SF1)) for SF1 while SFF2 allocates and
advertises an SID ( i.e., SID(SF2)) for SF2. These SIDs which are
used to indicate SFs are referred to as SF SIDs. To encode the SFP
information by an MPLS label stack, those SF SIDs as mentioned above
would be interpreted as local MPLS labels. In addition, assume node
SIDs for SFF1 and SFF2 are SID(SFF1) and SID(SFF2) respectively. Now
assume a given traffic flow destined for destination D is selected by
the service classifier to go through a particular SFC (i.e., SF1->
SF2) before reaching its final destination D. Section 3.1 describes
how to leverage the MPLS- based source routing mechanisms to realize
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the service path functionality of the service function chaining
(i.e., by encoding the SFP information within an MPLS label stack).
Section 3.2 describes how to carry metadata over MPLS packets.
3.1. Encoding SFP Information by an MPLS Label Stack
Since the selected packet needs to travel through an SFC (i.e.,
SF1->SF2), the service classifier would attach a segment list of
(i.e., SID(SFF1)->SID(SF1)->SID(SFF2)-> SID(SF2)) which indicates the
corresponding SFP to the packet. This segment list is actually
represented by a MPLS label stack. To some extent, the MPLS label
stack here could be looked as a specific implementation of the SFC
encapsulation used for containing the SFP information
[I-D.ietf-sfc-architecture]. When the encapsulated packet arrives at
SFF1, SFF1 would know which SF should be performed according to the
current top label (i.e., SID (SF1)) of the received MPLS packet. If
SF1 is an SFC encapsulation-aware SF, the MPLS packet would be sent
to SF1 after the top label is poped. After receiving the MPLS packet
returned from SF1, SFF1 would send it to SFF2 according to the
current top label (i.e., SID (SFF2) ). If SF1 is a legacy SF which
could not process the MPLS label stack, the whole MPLS label stack
(i.e., SID(SFF2)->SID(SF2)) MUST be stripped before sending the
packet to SF1. After receiving the packet returned from SF1, SFF1
would re-impose the MPLS label stack which had been stripped before
to the packet and then send it to SFF2 according to the current top
label (i.e., SID (SFF2) ). When the encapsulated packet arrives at
SFF2, SFF2 would perform the similar action as what has been done by
SFF1.
If there is no MPLS LSP towards the next node segment (i.e., the next
SFF identified by the current top label), the corresponding IP-based
tunnel (e.g., MPLS-in-IP/GRE tunnel [RFC4023], MPLS-in-UDP tunnel
[RFC7510] or MPLS-in-L2TPv3 tunnel [RFC4817]) could be used instead
(For more details about this special usage, please refer to
[I-D.xu-spring-islands-connection-over-ip]). Since the transport
(i.e., the underlay) could be IPv4, IPv6 or even MPLS networks, the
above approach of encoding the SFP information by an MPLS label stack
is fully transport-independent which is one of the major requirements
for the SFC encapsulation [I-D.ietf-sfc-architecture].
In addition, the service classifier could further impose metadata on
the MPLS packet through the Network Service Header (NSH)
[I-D.ietf-sfc-nsh] (As for how to contain the NSH within a MPLS
packet, please see Section 3.3). Here the Service Path field wihin
the NSH would not be used for the path selection purpose anymore and
therefore it MUST be set to a particular value to indicate such
particular usage. In addition, the service index value within the
NSH is set to a value indicating the total number of SFs within the
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service function path. The service index SHOULD be decreased by one
on each SF or SFC-proxy on behalf of the corresponding legacy SF.
When the service index become zero, the NSH MUST be removed from the
packet by the SF or SFC-proxy on behalf of the corresponding legacy
SF.
3.2. How to Contain Metadata within an MPLS Packet
Since the MPLS encapsulation has no explicit protocol identifier
field to indicate the protocol type of the MPLS payload, how to
indicate the presence of metadata (i.e., the NSH which is only used
as a metadata containner) in MPLS packets is a potential issue.
There is a possible way to address the above issue: SFFs allocate two
different labels for a given SF, one indicates the presence of NSH
while the other indicates the absence of NSH. This approach has no
change to the current MPLS architecture but it would require more
than one label binding for a given SF. More details about how to
contain metadata within an MPLS packet would be considered in the
future version of this draft.
4. Acknowledgements
The authors would like to thank Loa Andersson and Andrew G. Malis
for their valuable comments and suggestions on the draft. The
authors would like to thank Adrian Farrel, Stewart Bryant, Alexander
Vainshtein, Joel M. Halpern for their comments on how to indicate
the presence of metadata within an MPLS packet.
5. IANA Considerations
TBD.
6. Security Considerations
TBD
7. References
7.1. Normative 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-spring-segment-routing-mpls]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Shakir, R., Tantsura, J.,
and E. Crabbe, "Segment Routing with MPLS data plane",
draft-ietf-spring-segment-routing-mpls-03 (work in
progress), February 2016.
[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>.
7.2. Informative References
[I-D.ietf-sfc-nsh]
Quinn, P. and U. Elzur, "Network Service Header", draft-
ietf-sfc-nsh-02 (work in progress), January 2016.
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
and R. Shakir, "Segment Routing Architecture", draft-ietf-
spring-segment-routing-07 (work in progress), December
2015.
[I-D.xu-spring-islands-connection-over-ip]
Xu, X., Raszuk, R., Chunduri, U., and L. Contreras,
"Connecting MPLS-SPRING Islands over IP Networks", draft-
xu-spring-islands-connection-over-ip-04 (work in
progress), March 2015.
[RFC4023] Worster, T., Rekhter, Y., and E. Rosen, Ed.,
"Encapsulating MPLS in IP or Generic Routing Encapsulation
(GRE)", RFC 4023, DOI 10.17487/RFC4023, March 2005,
<http://www.rfc-editor.org/info/rfc4023>.
[RFC4817] Townsley, M., Pignataro, C., Wainner, S., Seely, T., and
J. Young, "Encapsulation of MPLS over Layer 2 Tunneling
Protocol Version 3", RFC 4817, DOI 10.17487/RFC4817, March
2007, <http://www.rfc-editor.org/info/rfc4817>.
[RFC7510] Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
"Encapsulating MPLS in UDP", RFC 7510,
DOI 10.17487/RFC7510, April 2015,
<http://www.rfc-editor.org/info/rfc7510>.
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Authors' Addresses
Xiaohu Xu
Huawei
Email: xuxiaohu@huawei.com
Zhenbin Li
Huawei
Email: lizhenbin@huawei.com
Himanshu Shah
Ciena
Email: hshah@ciena.com
Luis M. Contreras
Telefonica I+D
Ronda de la Comunicacion, s/n
Sur-3 building, 3rd floor
Madrid, 28050
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
URI: http://people.tid.es/LuisM.Contreras/
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