Service Function Chaining Using MPLS-SPRING
draft-xu-sfc-using-mpls-spring-00
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| Authors | Xiaohu Xu , Zhenbin Li , Himanshu C. Shah , Luis M. Contreras | ||
| Last updated | 2014-09-25 | ||
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draft-xu-sfc-using-mpls-spring-00
Network Working Group X. Xu
Internet-Draft Z. Li
Intended status: Informational Huawei
Expires: March 29, 2015 H. Shah
Ciena
L. Contreras
Telefonica I+D
September 25, 2014
Service Function Chaining Using MPLS-SPRING
draft-xu-sfc-using-mpls-spring-00
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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This Internet-Draft will expire on March 29, 2015.
Copyright Notice
Copyright (c) 2014 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. Encoding SFC Information by an MPLS Label Stack . . . . . 4
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 . . . . . . . . . . . . . . . . . . . . . . . 6
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 SPF 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, the SFC or the partially specified 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.gredler-spring-mpls]
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[I-D.filsfils-spring-segment-routing-mpls] and IPv6 data plane. This
document only describes how to leverage the MPLS-based source routing
mechanisms to realize the service path layer functionality of the
service function chaining. How to leverage the IPv6-based source
routing mechanism will be discried in a separate document.
Furthermore, how to carry metadata within MPLS packet would be
described in a separate document as well.
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.filsfils-spring-segment-routing] and
[I-D.ietf-sfc-architecture].
3. Solution Description
+----------------------------------------------- ----+
| SPRING Netowrks |
| +---------+ +---------+ |
| | 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 Forwarder (SFF) nodes
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. To
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simplify the illustration in this document, those node SIDs would be
interpreted as domain-wide unique MPLS labels as well. 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 and 3.2
describe two approaches of leveraging the MPLS- based source routing
mechanisms to realize the service path functionality of the service
function chaining (i.e., by encoding the SFP information within an
MPLS label stack or by encoding the SFC information within an MPLS
label stack) respectively.
3.1. Encoding SFP Information by an MPLS Label Stack
Since the selected packet needs to travel through an SFC {SF1, SF2},
the service classifier would attach a segment list {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. 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)). Before sending the packet to SF1, the
remaining MPLS label stack (i.e., a segment list {SID(SFF2),
SID(SF2)}) MUST be stripped. After receiving the packet returned
from SF1, SFF1 would reimpose 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 do the similar action as what has
been done by SFF1. Provided that there was no MPLS LSP tunnel
towards the next node segment (i.e., the next SFF node identified by
the current top label), the corresponding IP-based tunnel (e.g.,
MPLS-in-IP/GRE tunnel [RFC4023], MPLS-in-L2TPv3 tunnel [RFC4817] or
MPLS-in-UDP tunnel [I-D.ietf-mpls-in-udp]) towards the next node
segment could be used instead. For more details about this special
usage, please refer to [I-D.xu-spring-islands-connection-over-ip].
This approach of encoding the SFP information by an MPLS label stack
is transport independent since the transport (i.e., the underlay)
protocol could be IPv4, IPv6 or even MPLS. In other words, it fully
meets the requirement of transport independence for the SFC
encapsulation as mentioned in [I-D.ietf-sfc-architecture].
3.2. Encoding SFC 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 {SID(SF1),
SID(SF2)} which indicates that SFC to the packet. This segment list
is actually represented by a MPLS label stack. Since it's known to
the service classifier that SFF1 is attached with an instance of SF1,
the service classifier would therefore send the encapsulated packet
through either an MPLS LSP tunnel or an IP-based tunnel towards SFF1.
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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)). Before sending the packet to SF1, the remaining MPLS label
stack (i.e., a segment list {SID(SF2)}) MUST be stripped. Upon
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 through either an MPLS LSP tunnel or an IP-based
tunnel towards SFF2 since it's known to SFF1 that SFF2 is attached
with an instance of SF2. When the encapsulated packet arrives at
SFF2, SFF2 would do the similar action as what has been done by SFF1.
This approach of encoding the SFC information by an MPLS label stack
is transport independent since the transport (i.e., the underlay)
protocol could be IPv4, IPv6 or even MPLS. In other words, it fully
meets the requirement of transport independence for the SFC
encapsulation as mentioned in [I-D.ietf-sfc-architecture].
4. Acknowledgements
The authors would like to thank Loa Andersson and Andrew G. Malis
for their valuable comments and suggestions on the draft.
5. IANA Considerations
TBD.
6. Security Considerations
TBD
7. References
7.1. Normative References
[I-D.filsfils-spring-segment-routing-mpls]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
"Segment Routing with MPLS data plane", draft-filsfils-
spring-segment-routing-mpls-03 (work in progress), August
2014.
[I-D.gredler-spring-mpls]
Gredler, H., Rekhter, Y., Jalil, L., Kini, S., and X. Xu,
"Supporting Source/Explicitly Routed Tunnels via Stacked
LSPs", draft-gredler-spring-mpls-06 (work in progress),
May 2014.
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[I-D.xu-spring-islands-connection-over-ip]
Xu, X., Raszuk, R., Chunduri, U., and V. Lopezalvarez,
"Connecting MPLS-SPRING Islands over IP Networks", draft-
xu-spring-islands-connection-over-ip-02 (work in
progress), August 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
7.2. Informative References
[I-D.filsfils-spring-segment-routing]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
"Segment Routing Architecture", draft-filsfils-spring-
segment-routing-04 (work in progress), July 2014.
[I-D.ietf-mpls-in-udp]
Xu, X., Sheth, N., Yong, L., Pignataro, C., and F.
Yongbing, "Encapsulating MPLS in UDP", draft-ietf-mpls-in-
udp-05 (work in progress), January 2014.
[I-D.ietf-sfc-architecture]
Halpern, J. and C. Pignataro, "Service Function Chaining
(SFC) Architecture", draft-ietf-sfc-architecture-02 (work
in progress), September 2014.
[RFC4023] Worster, T., Rekhter, Y., and E. Rosen, "Encapsulating
MPLS in IP or Generic Routing Encapsulation (GRE)", RFC
4023, March 2005.
[RFC4817] Townsley, M., Pignataro, C., Wainner, S., Seely, T., and
J. Young, "Encapsulation of MPLS over Layer 2 Tunneling
Protocol Version 3", RFC 4817, March 2007.
Authors' Addresses
Xiaohu Xu
Huawei
Email: xuxiaohu@huawei.com
Zhenbin Li
Huawei
Email: lizhenbin@huawei.com
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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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