SFC M. Boucadair
Internet-Draft Orange
Intended status: Standards Track D. von Hugo
Expires: May 18, 2019 Deutsche Telekom
B. Sarikaya
Denpel Informatique
November 14, 2018
Service Function Chaining: Subscriber and Policy Identification
Variable-Length Network Service Header (NSH) Context Headers
draft-sfc-serviceid-header-02
Abstract
This document discusses how to inform Service Functions about
subscriber- and service-related information for the sake of policy
enforcement and appropriate service function chaining operations.
Status of This Memo
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This Internet-Draft will expire on May 18, 2019.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
3. Subscriber Identification NSH Variable-Length Context Header 4
4. Policy Identification NSH Variable-Length Context Headers . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
This document discusses how to inform Service Functions (SFs) about
subscriber- and service-related information when required for the
sake of policy enforcement within a single administrative domain.
Particularly, subscriber-related information may be required to
enforce subscriber-specific SFC-based traffic policies.
Nevertheless, the information carried in packets may not be
sufficient to unambiguously identify a subscriber. This document
fills this void by specifying a new Network Service Header (NSH)
[RFC8300] context header to convey and disseminate such information.
Also, the enforcement of SFC-based differentiated traffic policies
may be inferred by QoS considerations. Typically, QoS information
may serve as an input to classification of the Service Function Path
(SFP) for path computation, establishment, and selection.
Furthermore, the dynamic structuring of service function chains and
their subsequent enforcement may be conditioned by QoS requirements
that will affect SF instance identification, location, and
sequencing. Hence, the need to supply a policy identifier to
upstream SFs to appropriately meet the service requirements.
SFs and SF Forwarders (SFFs) involved in a service chain have to
contribute to the respective service policy (QoS, for example)
requirements characterized by low transmission delay between each
other, by exposing a high availability of resources to process
function tasks, or by redundancy provided by stand-by machines for
seamless execution continuation in case of failures. These
requirements may be satisfied by means of control protocols, but in
some contexts, (e.g., in networks where resources are very much
constrained), carrying QoS-related information directly in packets
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may improve the overall SFC operation instead of relying upon the
potential complexity or adding overhead introduced by some SFC
control plane features. This information is typically included as
metadata in the NSH as the SFC encapsulation to provide the SFP
identification.
The context information defined in this document can be applicable in
the context of mobile networks (typically, in the 3GPP defined (S)Gi
Interface) [I-D.ietf-sfc-use-case-mobility]. Because of the
widespread use of private addressing in those networks, if SFs to be
invoked are located after a NAT function (that can reside in the
Packet Data Network (PDN) Gateway (PGW) or in a distinct node), the
identification based on the internal IP address is not anymore
possible once the NAT has been crossed. As such, means to allow
passing the internal information may optimise packet traversal within
an SFC-enabled mobile network domain. Furthermore, some SFs that are
not enabled on the PGW may require a subscriber identifier to
properly operate.
This document does not make any assumption about the structure of
subscriber or policy identifiers; each such identifier is treated as
an opaque value by the SFC operations and protocols. The semantics
and validation of these identifiers are up to the control plane used
for SFC. Expectations to SFC control plane protocols are laid down,
e.g., in [RFC8459], but specifications of SFC control plane
functionalities are also discussed in, for example,
[I-D.ietf-bess-nsh-bgp-control-plane],
[I-D.wu-pce-traffic-steering-sfc], or [I-D.maglione-sfc-nsh-radius].
The use cases considered in this document assume the NSH is used
exclusively within a single administrative domain.
This document adheres to the architecture defined in [RFC7665]. This
document assumes the reader is familiar with [RFC8300].
2. Conventions and Terminology
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.
The reader should be familiar with the terms defined in [RFC7665].
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3. Subscriber Identification NSH Variable-Length Context Header
Subscriber Identifier is defined as an optional variable-length NSH
context header. Its structure is shown in Figure 1.
The subscriber identifier is used to convey an identifier already
assigned by the service provider to uniquely identify a subscriber.
This header conveys an opaque subscriber Identifier that can be used
by the service functions to enforce per-subscriber policies.
The classifier and SFC-aware SFs MAY be instructed via a control
interface to inject or strip a subscriber identifier context header.
Also, the data to be injected in such header SHOULD be configured to
nodes authorized to inject such headers. Typically, a node can be
instructed to insert such data following a type/set scheme (e.g.,
node X should inject subscriber ID type Y). Other schemes may be
envisaged.
Failures to inject such headers SHOULD be logged locally while a
notification alarm MAY be sent to a Control Element. The details of
sending notification alarms (i.e., the parameters affecting the
transmission of the notification alarms depend on the information in
the context header such as frequency, thresholds, and content in the
alarm (full header, header ID, timestamp), etc.) SHOULD be
configurable by the control plane.
This document adheres to the recommendations in [RFC8300] for
handling the context headers at both ingress and egress SFC boundary
nodes. That is, to strip such context headers. Revealing any
personal and subscriber-related information to third parties is
avoided by design to prevent privacy breaches in terms of user
tracking.
SFC-aware SFs and proxies MAY be instructed to strip a subscriber
identifier context header from the packet or to pass the data to the
next SF in the service chain after processing the content of the
context headers. If no instruction is provided, the default behavior
is to maintain such context headers so that the information can be
passed to next SFC-aware hops.
SFC-aware SFs MAY be instructed via the control plane about the
validation checks to run on the content of these context headers
(e.g., accept only some lengths) and the behavior to adopt. For
example, SFC-aware SFs may be instructed to ignore the context
header, to remove the context header from the packet, etc.
Nevertheless, this specification does not require nor preclude such
additional validation checks. These validation checks are
deployment-specific. If validation checks fail on a subscriber
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identifier context header, an SFC-aware SF MUST ignore that context
header. The event SHOULD be logged locally while a notification
alarm MAY be sent to a Control Element if the SFC-aware SF is
instructed to do so.
Multiple subscriber Identifier context TLVs MAY be present in the NSH
each carrying a distinct opaque value but all pointing to the same
subscriber. When multiple subscriber Identifier context TLVs are
present and an SF is instructed to strip the subscriber Identifier
context header, that SF has to remove all subscriber Identifier
context TLVs.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class | Type |U| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Subscriber Identifier ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Subscriber Identifier Variable-Length Context Header
The description of the fields is as follows:
o Metadata Class: MUST be set to 0x0 [RFC8300].
o Type: TBD1 (See Section 5)
o Subscriber Identifier: Carries an opaque subscriber identifier.
4. Policy Identification NSH Variable-Length Context Headers
Dedicated service-specific performance identifier is defined to
differentiate between services requiring specific treatment to
exhibit a performance characterized by, e.g., ultra-low latency (ULL)
or ultra-high reliability (UHR). Other policies can be considered
when instantiating a service function chain within an SFC-enabled
domain. They are contained in the Policy Identifier context header.
The policy identifier is inserted in an NSH packet so that upstream
SFC-aware nodes can make use of the information for proper
distributed SFC path selection, SF instance selection, or policy
selection at SFs.
Thus, the policy identifier allows for the distributed enforcement of
a per-service policy such as a service function path to only include
specific SFs instances. Details of this process are implementation-
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specific. For illustration purposes, an SFF may retrieve the details
of usable SFs based upon the corresponding policy identifier.
Typical criteria for instantiating specific SFs include location,
performance, or proximity considerations. For the particular case of
UHR services, the stand-by operation of back-up capacity or the
deployment of multiple SF instances may be requested.
Policy identifier is defined as optional variable length context
header. Its structure is shown in Figure 2.
Similar control plane considerations as those discussed in Section 3
are to be followed.
Multiple policy identifier context headers MAY be present in the NSH;
each carrying a distinct opaque value but all are pointing to
policies that need to be enforced for a flow. It is up to the
control plane to ensure that these policies are not conflicting.
When such conflict is detected by an SFC-aware node, the default
behavior of the node is to discard the packet and send a notification
alarm to a Control Element.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class | Type |U| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Policy Identifier ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Policy Identifier Variable-Length Context Header
The description of the fields is as follows:
o Metadata Class: MUST be set to 0x0 [RFC8300].
o Type: TBD2 (See Section 5)
o Policy Identifier: Represents an opaque value pointing to specific
policy to be enforced. The structure and semantic of this filed
is deployment-specific.
5. IANA Considerations
This document requests IANA to assign the following types from the
"NSH IETF- Assigned Optional Variable-Length Metadata Types" (0x0000
IETF Base NSH MD Class) registry available at:
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https://www.iana.org/assignments/nsh/nsh.xhtml#optional-variable-
length-metadata-types.
+-------+-----------------------+----------------+
| Value | Description | Reference |
+-------+-----------------------+----------------+
| TBD1 | Subscriber Identifier | [ThisDocument] |
| TBD2 | Policy Identifier | [ThisDocument] |
+-------+-----------------------+----------------+
6. Security Considerations
Data plane SFC-related security considerations, including privacy,
are discussed in [RFC7665] and [RFC8300].
Nodes that are involved in an SFC-enabled domain are assumed to be
trusted ([RFC8300]). Means to check that only authorized nodes are
solicited when a packet is crossing an SFC-enabled domain.
An SF maintaining logs for operational reasons MUST NOT log the
content of subscriber identifier context header received in NSH
packets if the SF does not use the content of that header for its
operation.
7. Acknowledgements
Comments from Joel Halpern on a previous version and by Carlos
Bernardos are appreciated. Contributions and review by Christian
Jacquenet, Danny Lachos, Debashish Purkayastha, Christian Esteve
Rothenberg, and Kyle Larose are thankfully acknowledged.
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>.
[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>.
[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>.
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[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>.
8.2. Informative References
[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-04 (work in progress), July 2018.
[I-D.ietf-sfc-use-case-mobility]
Napper, J., Stiemerling, M., Lopez, D., and J. Uttaro,
"Service Function Chaining Use Cases in Mobile Networks",
draft-ietf-sfc-use-case-mobility-08 (work in progress),
May 2018.
[I-D.maglione-sfc-nsh-radius]
Maglione, R., Trueba, G., and C. Pignataro, "RADIUS
Attributes for NSH", draft-maglione-sfc-nsh-radius-01
(work in progress), October 2016.
[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.
[RFC8459] Dolson, D., Homma, S., Lopez, D., and M. Boucadair,
"Hierarchical Service Function Chaining (hSFC)", RFC 8459,
DOI 10.17487/RFC8459, September 2018,
<https://www.rfc-editor.org/info/rfc8459>.
Authors' Addresses
Mohamed Boucadair
Orange
Rennes 3500
France
Email: mohamed.boucadair@orange.com
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Dirk von Hugo
Deutsche Telekom
Deutsche-Telekom-Allee 7
D-64295 Darmstadt
Germany
Email: Dirk.von-Hugo@telekom.de
Behcet Sarikaya
Denpel Informatique
Email: sarikaya@ieee.org
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