SFC B. Sarikaya
Internet-Draft Denpel Informatique
Intended status: Standards Track M. Boucadair
Expires: April 18, 2019 Orange
D. von Hugo
Deutsche Telekom
October 15, 2018
Service Function Chaining: Subscriber and Policy Identification
Variable-Length NSH Context Headers
draft-sfc-serviceid-header-00
Abstract
This document discusses how to inform Service Functions (SFs) about
subscriber- and service-related information for the sake of policy
enforcement and appropriate SFC-inferred forwarding.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4
3. Subscriber Identification NSH Variable-Length Context Header 4
4. Policy Identification NSH Variable-Length Context Headers . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
This document discusses how to inform Service Functions about
subscriber- and service-related information when required for the
sake of policy enforcement. Indeed, subscriber-related information
may be required to enforce subscriber-specific, SFC-based traffic
forwarding policies, since the information carried in packets may not
be sufficient.
The enforcement of SFC-based differentiated traffic forwarding
policies may also be inferred by QoS considerations. QoS information
may serve as an input to classification of the Service Function Path
(SFP) for path computation and establishment.
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.
Since network and path conditions may change dynamically based on
e.g. traffic load and radio path variations the path decision and
configuration mechanisms have to reflect the potentially changing
context and consider corresponding information network.
SFs and SF Forwarders (SFFs) involved in an SFC have to contribute to
the respective QoS 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
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are very much constrained), carrying QoS-related information directly
in packets 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 e.g. included as
metadata in the Network Service Header (NSH) [RFC8300] as the SFC
encapsulation to provide the SFP identification.
This document adheres to the architecture defined in [RFC7665]. This
document assumes the reader is familiar with [RFC7665], [RFC8459] and
[RFC8300].
Metadata defined in this document may be required to implement
services such as, but not limited to, traffic policy control,
parental control, traffic offload. Such features are often provided
by operators as part of their service portfolio.
Another example is the applicability of service chaining 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 advanced
SFs to be invoked are located after a NAT device (that can reside in
the Packet Data Network (PDN) Gateway (PGW) or in a distinct
operator-specific 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. Other use cases that
suffer from identification problems further are discussed in
[RFC7620].
This document does not make any assumption about the structure of
policy identifiers; each such service-related information 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
[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.
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2. Conventions and Terminology
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].
The reader should be familiar with the terms defined in [RFC7665].
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 may convey an opaque subscriber Identifier, a domain-
local encoding of the subscriber identity that can be used by the
service functions to find appropriate policy, state, or similar
information.
Revealing any personal and subscriber-related information to third
parties must be avoided to prevent privacy breaches in terms of user
tracking etc.
The classifier and SFC-aware Service Functions 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. 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.
SFC-aware SFs and proxies MAY be instructed to strip a subscriber
identifier from the packet or to pass the data to the next SF in the
chain after processing the content of the 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 functions MAY be instructed via the control plane about the
validation checks to run on the content of these context headers
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(e.g., accept only some lengths, accept some subtypes) and the
behavior to adopt. For example, SFC-aware nodes 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 context
header, an SFC-aware node ignores that context header. The event
SHOULD be logged locally while a notification alarm MAY be sent to a
control element if the SFC-aware node is instructed to do so.
Multiple subscriber Identifier context TLVs MAY be present in the NSH
each carrying a distinct sub-type.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SubT | |
+-+-+-+-+-+-+-+-+
~ 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 SubT field of 8 bits indicates the sub-type of the information
conveyed in the "Subscriber Identifier" field. The following
values are defined:
* 0x00: Opaque value
* 0x02: Subscriber ID. The structure of this ID is deployment-
specific.
o Subscriber Identifier: Carries an opaque subscriber identifier or
an identifier that corresponds to the sub-type.
An agreement on standardized NSH elements as proposed above and in
the next section would allow for cross-vendor inter-operability
within an SFC domain, which according to [RFC7665] is limited to a
single network administrative domain. Thus with the proposed Context
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Headers size a large amount of subscribers, and services should be
supported and the approach would scale.
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). These parameters are related to
policy identifier, among others. They are contained in the Policy
Identifier. The policy Identifier thus allows for the enforcement of
a per service policy such as a service classification function to
only consider specific Service Function instances during service
function path establishment. Details of this process are
implementation- specific. For illustration purposes, the classifier
may retrieve the details of usable service functions based upon the
corresponding service ID. Typical criteria for instantiating
specific service functions include location, performance or proximity
considerations. For UHR services, the stand-by operation of back-up
capacity or the deployment of multiple service function instances may
be requested.
In other words, the classifier uses this kind of information to
decide about the set of SFFs to invoke to honor the latency or
reliability requirement (e.g., compute an Rendered Service Path, RSP,
or insert a pointer to be shared with involved SFFs).
Policy Identifier is defined as optional variable length context
header. Its structure is shown in Figure 2.
Policy Identifier context header MAY convey a user or service
provider defined unique identity which can be described by an opaque
value.
The service requirements in terms of, e.g., maximum latency or
minimum outage probability are specified by service providers and are
out of the scope of this document.
Multiple Policy Identifier context headers MAY be present in the NSH;
each carrying a distinct sub-type.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SubT | |
+-+-+-+-+-+-+-+-+
~ 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 SubT: 8-bit field that carries the sub-type of the information
conveyed in the "Policy Identifier" field. The following values
are defined:
* 0x00: Opaque value
* 0x03: Policy Identifier. The structure of this ID is service
deployment-specific.
* 0x04 - 0x08: reserved
o Policy Identifier: Represents a specific service performance
characteristic reflected in the SubT field, but also denotes a
default basic (best effort) service without specifically defined
requirements. It MAY also be an opaque value which semantic is
defined by the operator.
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:
https://www.iana.org/assignments/nsh/nsh.xhtml#optional-variable-
length-metadata-types.
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+------+-----------------------+----------------+
| C1 | C2 | |
+------+-----------------------+----------------+
| TBD1 | Subscriber Identifier | [ThisDocument] |
| TBD2 | Policy Identifier | [ThisDocument] |
+------+-----------------------+----------------+
6. Security Considerations
Data plane SFC-related security considerations 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.
7. Privacy Considerations
The metadata defined in this document does not include any privacy
related information.
8. 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, and Christian Esteve
Rothenberg are thankfully acknowledged.
9. References
9.1. 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>.
[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>.
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9.2. 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]
Haeffner, W., 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.
[RFC7620] Boucadair, M., Ed., Chatras, B., Reddy, T., Williams, B.,
and B. Sarikaya, "Scenarios with Host Identification
Complications", RFC 7620, DOI 10.17487/RFC7620, August
2015, <https://www.rfc-editor.org/info/rfc7620>.
[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
Behcet Sarikaya
Denpel Informatique
Email: sarikaya@ieee.org
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
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