Internet DRAFT - draft-xu-mpls-service-chaining
draft-xu-mpls-service-chaining
MPLS Working Group X. Xu
Internet-Draft S. Bryant
Intended status: Standards Track Huawei
Expires: December 31, 2017 H. Assarpour
Broadcom
H. Shah
Ciena
L. Contreras
Telefonica I+D
D. Bernier
Bell Canada
J. Tantsura
Individual
S. Ma
Juniper
M. Vigoureux
Nokia
June 29, 2017
Service Chaining using Unified Source Routing Instructions
draft-xu-mpls-service-chaining-03
Abstract
Source Packet Routing in Networking (SPRING) WG is developing an MPLS
source routing mechanism. The MPLS source routing mechanism can be
leveraged to realize a unified source routing instruction which works
across both IPv4 and IPv6 underlays in addition to the MPLS underlay.
This document describes how to leverage the unified source routing
instruction to realize a transport-independent service function
chaining by encoding the service function path information or service
function chain information as an MPLS label stack.
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].
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
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working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://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 31, 2017.
Copyright Notice
Copyright (c) 2017 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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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
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 . . . . . 7
3.3. How to Contain Metadata within an MPLS Packet . . . . . . 9
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
When applying a particular Service Function Chain (SFC) [RFC7665] 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. In order
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to steer the selected traffic through the required ordered list of
SFs, the service classifier needs to attach information to the packet
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.
The Source Packet Routing in Networking (SPRING) WG is developing an
MPLS source routing mechanism which can be used to steer traffic
through an ordered set of routers (i.e., an explicit path) and
instruct nodes on that path to execute specific operations on the
packet. By leveraging the MPLS source routing mechanism,
[I-D.xu-mpls-unified-source-routing-instruction] describes a unified
source routing instruction which works across both IPv4 and IPv6
underlays in addition to the MPLS underlay. This document describes
how to leverage the unified source routing instruction to realize a
transport-independent service function chaining by encoding the
service function path information or service function chain
information as an MPLS label stack.
2. Terminology
This memo makes use of the terms defined in
[I-D.ietf-spring-segment-routing-mpls],
[I-D.xu-mpls-unified-source-routing-instruction] and [RFC7665].
3. Solution Description
+----------------------------------------------- ----+
| MPLS SPRING Networks |
| +---------+ +---------+ |
| | SF1 | | SF2 | |
| +----+----+ +----+----+ |
| ^ | |(3) ^ | |(6) |
| (1) (2)| | V (4) (5)| | V (7) |
+----+-----+ ---> +----+----+ ----> +----+----+ ---> +---+---+
|Classifier+------+ SFF1 +-------+ SFF2 +-------+ D |
+----------+ +---------+ +---------+ +---+---+
| |
+----------------------------------------------------+
Figure 1: Service Function Chaining in MPLS-SPRING Networks
As shown in Figure 1, SFF1 and SFF2 are two MPLS-SPRING-capable
nodes. They are also SFFs, each with one SF attached. In addition,
they have allocated and advertised MPLS labels for their locally
attached SFs. For example, SFF1 allocates and advertises a label
(i.e., L(SF1)) for SF1 while SFF2 allocates and advertises a label (
i.e., L(SF2)) for SF2. These labels, which are used to indicate SFs
are referred to as SF labels. To encode the SFP information as an
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MPLS label stack, local MPLS labels are allocated from SFFs' (e.g.,
SFF1 in Figure 1) label spaces to identify their locally attached SFs
(e.g., SF1 in Figure 1), whilst the SFFs are identified by either
nodal SIDs or adjacency SIDs depending on how strictly the network
path needs to be specified. In addition, assume node SIDs for SFF1
and SFF2 are L(SFF1) and L(SFF2) respectively. In contrast, to
encode the SFC information by an MPLS label stack, those SF labels
MUST be domain-wide unique MPLS labels.
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 approaches of leveraging the MPLS- based
source routing mechanisms to realize the service function chaining by
encoding the SFP information within an MPLS label stack and by
encoding the SFC information within an MPLS label stack respectively.
Since the encoding of the partially specified SFP is just a simple
combination of the encoding of the SFP and the encoding of the SFC,
this document would not describe how to encode the partially
specified SFP anymore.
3.1. Encoding SFP Information by an MPLS Label Stack
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+----------------------------------------------- ----+
| MPLS SPRING Networks |
| +---------+ +---------+ |
| | SF1 | | SF2 | |
| +----+----+ +----+----+ |
| +---------+ | | +---------+ |
| | L(SFF2) | | | |Pkt to D | |
| +---------+ | | +---------+ |
| | L(SF2) | | | |
| +---------+ | ^ | | |
| |Pkt to D | ^ | | | | | |
| +---------+ | | | (5)| | |(6) |
| (2)| | |(3) | | V |
| (1) | | V (4) | (7) |
+----+-----+ ---> +----+----+ ----> +----+----+ ---> +---+---+
|Classifier+------+ SFF1 +-------+ SFF2 +-------+ D |
+----------+ +---------+ +---------+ +---+---+
| +---------+ +---------+ +---------+ |
| | L(SFF1) | | L(SFF2) | |Pkt to D | |
| +---------+ +---------+ +---------+ |
| | L(SF1) | | L(SF2) | |
| +---------+ +---------+ |
| | L(SFF2) | |Pkt to D | |
| +---------+ +---------+ |
| | L(SF2) | |
| +---------+ |
| |Pkt to D | |
| +---------+ |
+----------------------------------------------------+
Figure 2: Packet Walk in MPLS underlay
As shown in Figure 2, 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 represented by an 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 [RFC7665].
When the encapsulated packet arrives at SFF1, SFF1 would know which
SF should be performed according to the top label (i.e., SID (SF1))
of the received MPLS packet. We first consider the case where SF1 is
an encapsulation aware SF, i.e., it understands how to process a
packet with a pre-pended MPLS label stack. In this case the packet
would be sent to SF1 by SFF1 with the label stack SID(SFF2)->
SID(SF2). SF1 would perform the required service function on the
received MPLS packet where the payload is constrained to be an IP
packet, and the SF needs to process both IPv4 and IPv6 packets (note
that the SF would use the first nibble of the MPLS payload to
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identify the payload type). After the MPLS packet is returned from
SF1, SFF1 would send it to SFF2 according to the top label (i.e., SID
(SFF2) ).
If SF1 is a legacy SF, i.e. one that is unable to process the MPLS
label stack, the remaining MPLS label stack (i.e.,
SID(SFF2)->SID(SF2)) MUST be saved and stripped from the packet
before sending the packet to SF1. When the packet is returned from
SF1, SFF1 would re-impose the MPLS label stack which had been
previously stripped and then send the packet to SFF2 according to the
current top label (i.e., SID (SFF2) ). As for how to associate the
corresponding MPLS label stack with the packets returned from legacy
SFs, those mechanisms as described in
[I-D.song-sfc-legacy-sf-mapping] could be considered.
When the encapsulated packet arrives at SFF2, SFF2 would perform the
similar action to that described above.
As shown in Figure 3, 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 for MPLS (e.g., MPLS-in-IP/GRE tunnel
[RFC4023], MPLS-in-UDP tunnel [RFC7510] or MPLS-in-L2TPv3 tunnel
[RFC4817]) would be used instead, according to the unified source
routing instruction as described in
[I-D.xu-mpls-unified-source-routing-instruction].
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+----------------------------------------------- ----+
| IP Networks |
| +---------+ +---------+ |
| | SF1 | | SF2 | |
| +----+----+ +----+----+ |
| +---------+ | | +---------+ |
| | L(SFF2) | | | |Pkt to D | |
| +---------+ | | +---------+ |
| | L(SF2) | | | |
| +---------+ | ^ | | |
| |Pkt to D | ^ | | | | | |
| +---------+ | | | (5)| | |(6) |
| (2)| | |(3) | | V |
| (1) | | V (4) | (7) |
+----+-----+ ---> +----+----+ ----> +----+----+ ---> +---+---+
|Classifier+------+ SFF1 +-------+ SFF2 +-------+ D |
+----------+ +---------+ +---------+ +---+---+
| +---------+ +---------+ |
| |IP Tunnel| |IP Tunnel| +---------+ |
| |to SFF1 | | to SFF2 | |Pkt to D | |
| +---------+ +---------+ +---------+ |
| | L(SF1) | | L(SF2) | |
| +---------+ +---------+ |
| | L(SFF2) | |Pkt to D | |
| +---------+ +---------+ |
| | L(SF2) | |
| +---------+ |
| |Pkt to D | |
| +---------+ |
+----------------------------------------------------+
Figure 3: Packet Walk in IP underlay
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 [RFC7665].
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 an MPLS label stack
(i.e., L(SF1)->L(SF2)) which indicates that SFC to the packet. Since
it's known to the service classifier that SFF1 is attached with an
instance of SF1, the service classifier would therefore send the MPLS
encapsulated packet through either an MPLS LSP tunnel or an IP-based
tunnel towards SFF1 (as shown in Figure 4 and 5 respectively). When
the MPLS encapsulated packet arrives at SFF1, SFF1 would know which
SF should be performed according to the current top label (i.e.,
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L(SF1)). Similarly, SFF1 would send the packet returned from SF1 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. Since the
transport (i.e., the underlay) could be IPv4, IPv6 or even MPLS
networks, the above approach of encoding the SFC information by an
MPLS label stack is fully transport-independent which is one of the
major requirements for the SFC encapsulation [RFC7665].
+----------------------------------------------- ----+
| MPLS Networks |
| +---------+ +---------+ |
| | SF1 | | SF2 | |
| +----+----+ +----+----+ |
| | | +---------+ |
| | | |Pkt to D | |
| +---------+ | | +---------+ |
| | L(SF2) | | | |
| +---------+ | ^ | | |
| |Pkt to D | ^ | | | | | |
| +---------+ | | | (5)| | |(6) |
| (2)| | |(3) | | V |
| (1) | | V (4) | (7) |
+----+-----+ ---> +----+----+ ----> +----+----+ ---> +---+---+
|Classifier+------+ SFF1 +-------+ SFF2 +-------+ D |
+----------+ +---------+ +---------+ +---+---+
| +---------+ +---------+ +---------+ |
| | L(SFF1) | | L(SFF2) | |Pkt to D | |
| +---------+ +---------+ +---------+ |
| | L(SF1) | | L(SF2) | |
| +---------+ +---------+ |
| | L(SF2) | |Pkt to D | |
| +---------+ +---------+ |
| |Pkt to D | |
| +---------+ |
+----------------------------------------------------+
Figure 4: Packet Walk in MPLS underlay
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+----------------------------------------------- ----+
| IP Networks |
| +---------+ +---------+ |
| | SF1 | | SF2 | |
| +----+----+ +----+----+ |
| | | +---------+ |
| | | |Pkt to D | |
| +---------+ | | +---------+ |
| | L(SF2) | | | |
| +---------+ | ^ | | |
| |Pkt to D | ^ | | | | | |
| +---------+ | | | (5)| | |(6) |
| (2)| | |(3) | | V |
| (1) | | V (4) | (7) |
+----+-----+ ---> +----+----+ ----> +----+----+ ---> +---+---+
|Classifier+------+ SFF1 +-------+ SFF2 +-------+ D |
+----------+ +---------+ +---------+ +---+---+
| +---------+ +---------+ |
| |IP Tunnel| |IP Tunnel| +---------+ |
| |to SFF1 | | to SFF2 | |Pkt to D | |
| +---------+ +---------+ +---------+ |
| | L(SF1) | | L(SF2) | |
| +---------+ +---------+ |
| | L(SF2) | |Pkt to D | |
| +---------+ +---------+ |
| |Pkt to D | |
| +---------+ |
+----------------------------------------------------+
Figure 5: Packet Walk in IP underlay
3.3. 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 an MPLS packet is a potential issue to
be addressed. One possible way to address the above issue is: 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. Another possible
way is to introduce a protocol identifier field within the MPLS
packet as described in [I-D.xu-mpls-payload-protocol-identifier].
More details about how to contain metadata within an MPLS packet
would be considered in the future version of this draft.
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4. Acknowledgements
The authors would like to thank Loa Andersson, Andrew G. Malis,
Adrian Farrel, Alexander Vainshtein and Joel M. Halpern for their
valuable comments and suggestions on the document.
5. IANA Considerations
This document makes no request of IANA.
6. Security Considerations
It is fundamental to the SFC design that the classifier is a trusted
resource which determines the processing that the packet will be
subject to, including for example the firewall. It is also
fundamental to the SPRING design that packets are routed through the
network using the path specified by the node imposing the SIDs.
Where an SF is not encapsulation aware the packet may exist as an IP
packet, however this is an intrinsic part of the SFC design which
needs to define how a packet is protected in that environment. Where
a tunnel is used to link two non-MPLS domains, the tunnel design
needs to specify how it is secured. Thus the secutity
vulnerabilities are addressed in the underlying technologies used by
this design, which itself does not introduce any new security
vulnerabilities.
7. References
7.1. 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,
<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-12 (work in progress), February 2017.
[I-D.ietf-spring-segment-routing-mpls]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-10
(work in progress), June 2017.
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[I-D.song-sfc-legacy-sf-mapping]
Song, H., You, J., Yong, L., Jiang, Y., Dunbar, L.,
Bouthors, N., and D. Dolson, "SFC Header Mapping for
Legacy SF", draft-song-sfc-legacy-sf-mapping-08 (work in
progress), September 2016.
[I-D.xu-mpls-payload-protocol-identifier]
Xu, X., "MPLS Payload Protocol Identifier", draft-xu-mpls-
payload-protocol-identifier-02 (work in progress),
December 2016.
[I-D.xu-mpls-unified-source-routing-instruction]
Xu, X., Bryant, S., Raszuk, R., Chunduri, U., Contreras,
L., Jalil, L., Assarpour, H., Velde, G., Tantsura, J., and
S. Ma, "Unified Source Routing Instruction using MPLS
Label Stack", draft-xu-mpls-unified-source-routing-
instruction-02 (work in progress), June 2017.
[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>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<http://www.rfc-editor.org/info/rfc7665>.
Authors' Addresses
Xiaohu Xu
Huawei
Email: xuxiaohu@huawei.com
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Stewart Bryant
Huawei
Email: stewart.bryant@gmail.com
Hamid Assarpour
Broadcom
Email: hamid.assarpour@broadcom.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/
Daniel Bernier
Bell Canada
Email: daniel.bernier@bell.ca
Jeff Tantsura
Individual
Email: jefftant@gmail.com
Shaowen Ma
Juniper
Email: mashaowen@gmail.com
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Martin Vigoureux
Nokia
Email: martin.vigoureux@nokia.com
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