Internet DRAFT - draft-quinn-nsh
draft-quinn-nsh
Network Working Group P. Quinn
Internet-Draft J. Guichard
Intended status: Standards Track R. Fernando
Expires: August 16, 2014 S. Kumar
M. Smith
N. Yadav
Cisco Systems, Inc.
P. Agarwal
R. Manur
Broadcom
A. Chauhan
Citrix
B. McConnell
Rackspace
C. Wright
Red Hat Inc.
February 12, 2014
Network Service Header
draft-quinn-nsh-02.txt
Abstract
This draft describes a Network Service Header (NSH) added to
encapsulated packets or frames to realize service function paths.
NSH also provides a mechanism for metadata exchange along the
instantiated service path.
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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].
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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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 16, 2014.
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. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Definition of Terms . . . . . . . . . . . . . . . . . . . 4
2.2. Problem Space . . . . . . . . . . . . . . . . . . . . . . 6
3. Network Service Header . . . . . . . . . . . . . . . . . . . . 8
3.1. NSH Actions . . . . . . . . . . . . . . . . . . . . . . . 8
3.2. NSH Encapsulation . . . . . . . . . . . . . . . . . . . . 9
3.3. NSH Usage . . . . . . . . . . . . . . . . . . . . . . . . 10
3.4. NSH Proxy Nodes . . . . . . . . . . . . . . . . . . . . . 10
4. Header Format . . . . . . . . . . . . . . . . . . . . . . . . 12
5. NSH Example: GRE . . . . . . . . . . . . . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
9.1. Normative References . . . . . . . . . . . . . . . . . . . 19
9.2. Informative References . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
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2. Introduction
Service functions are widely deployed and essential in many networks.
These service functions provide a range of features such as security,
WAN acceleration, and server load balancing. Service functions may
be instantiated at different points in the network infrastructure
such as the wide area network, data center, campus, and so forth.
The current service function deployment models are relatively static,
and bound to topology for insertion and policy selection.
Furthermore, they do not adapt well to elastic service environments
enabled by virtualization.
New data center network and cloud architectures require more flexible
service function deployment models. Additionally, the transition to
virtual platforms requires an agile service insertion model that
supports elastic service delivery; the movement of service functions
and application workloads in the network and the ability to easily
bind service policy to granular information such as per-subscriber
state are necessary.
The approach taken by NSH is composed of two elements:
1. Fixed size, transport independent per-packet/frame service meta-
data
2. Data plane encapsulation that utilizes the network overlay
topology used to deliver packets to the requisite services.
NSH is designed to be easy to implement across a range of devices,
both physical and virtual, including hardware platforms.
An NSH aware control plane is outside the scope of this document.
The SFC Architecture document [SFC-arch] provides an overview of a
chaining architecture that clearly defines the roles of the various
elements and the scope of a service function chaining encapsulation.
2.1. Definition of Terms
Classification: Locally instantiated policy and customer/network/
service profile matching of traffic flows for identification of
appropriate outbound forwarding actions.
SFC Network Forwarder (SFCNF): SFC network forwarders provide
network connectivity for service functions forwarders and service
functions. SFC network forwarders participate in the network
overlay used for service function chaining as well as in the SFC
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encapsulation.
Service Function Forwarder (SFF): A service function forwarder is
responsible for delivering traffic received from the SFCNF to one
or more connected service functions, and from service functions to
the SFCNF.
Service Function (SF): A function that is responsible for specific
treatment of received packets. A service function can act at the
network layer or other OSI layers. A service function can be a
virtual instance or be embedded in a physical network element.
One of multiple service functions can be embedded in the same
network element. Multiple instances of the service function can
be enabled in the same administrative domain.
Service Node (SN): Physical or virtual element that hosts one or
more service functions and has one or more network locators
associated with it for reachability and service delivery.
Service Function Chain (SFC): A service Function chain defines an
ordered set of service functions that must be applied to packets
and/or frames selected as a result of classification. The implied
order may not be a linear progression as the architecture allows
for nodes that copy to more than one branch. The term service
chain is often used as shorthand for service function chain.
Service Function Path (SFP): The instantiation of a SFC in the
network. Packets follow a service function path from a classifier
through the requisite service functions
Network Node/Element: Device that forwards packets or frames based
on outer header information. In most cases is not aware of the
presence of NSH.
Network Overlay: Logical network built on top of existing network
(the underlay). Packets are encapsulated or tunneled to create
the overlay network topology.
Network Service Header: Data plane header added to frames/packets.
The header contains information required for service chaining, as
well as metadata added and consumed by network nodes and service
elements.
Service Classifier: Function that performs classification and
imposes an NSH. Creates a service path. Non-initial (i.e.
subsequent) classification can occur as needed and can alter, or
create a new service path.
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Service Hop: NSH aware node, akin to an IP hop but in the service
overlay.
Service Path Segment: A segment of a service path overlay.
NSH Proxy: Acts as a gateway: removes and inserts NSH on behalf of a
service function that is not NSH aware.
2.2. Problem Space
Network Service Header (NSH) addresses several limitations associated
with service function deployments today.
1. Topological Dependencies: Network service deployments are often
coupled to network topology. Such dependency imposes constraints
on the service delivery, potentially inhibiting the network
operator from optimally utilizing service resources, and reduces
the flexibility. This limits scale, capacity, and redundancy
across network resources.
2. Service Chain Construction: Service function chains today are
most typically built through manual configuration processes.
These are slow and error prone. With the advent of newer service
deployment models the control/management planes provide not only
connectivity state, but will also be increasingly utilized for
the creation of network services. Such a control/management
planes could be centralized, or be distributed.
3. Application of Service Policy: Service functions rely on topology
information such as VLANs or packet (re) classification to
determine service policy selection, i.e. the service function
specific action taken. Topology information is increasingly less
viable due to scaling, tenancy and complexity reasons. The
topological information is often stale, providing the operator
with inaccurate placement that can result in suboptimal resource
utilization. Furthermore topology-centric information often does
not convey adequate information to the service functions, forcing
functions to individually perform more granular classification.
4. Per-Service (re)Classification: Classification occurs at each
service function independent from previously applied service
functions. More importantly, the classification functionality
often differs per service function and service functions may not
leverage the results from other service functions.
5. Common Header Format: Various proprietary methods are used to
share metadata and create service paths. An open header provides
a common format for all network and service devices.
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6. Limited End-to-End Service Visibility: Troubleshooting service
related issues is a complex process that involve both network-
specific and service-specific expertise. This is especially the
case when service function chains span multiple DCs, or across
administrative boundaries. Furthermore, the physical and virtual
environments (network and service), can be highly divergent in
terms of topology and that topological variance adds to these
challenges.
7. Transport Dependence: Service functions can and will be deployed
in networks with a range of transports, including under and
overlays. The coupling of service functions to topology requires
service functions to support many transports or for a transport
gateway function to be present.
Please see the Service Function Chaining Problem Statement [SFC-PS]
for a more detailed analysis of service function deployment problem
areas.
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3. Network Service Header
A Network Service Header (NSH) contains metadata and service path
information that is added to a packet or frame and used to create a
service plane. The packets and the NSH are then encapsulated in an
outer header for transport.
The service header is added by a service classification function - a
device or application - that determines which packets require
servicing, and correspondingly which service path to follow to apply
the appropriate service.
A NSH is composed of a 64-bit base header, and four 32-bit context
headers as shown in figure 1 below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Base Header |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Context Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Context Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Context Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Context Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Network Service Header
Base header: provides information about the service header and
service path identification.
Context headers: carry opaque metadata.
3.1. NSH Actions
Service header aware nodes - service classifiers, SFF, SF and NSH
proxies, have several possible header related actions:
1. Insert or remove service header: These actions can occur at the
start and end respectively of a service path. Packets are
classified, and if determined to require servicing, a service
header imposed. The last node in a service chain, an SF, or an
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associated SFF, removes NSH. A service classifier MUST insert a
NSH. At the end of a service function chain, the last node
operating on the service header MUST remove it.
A service function can re-classify data as required and that re-
classification might result in a new service path. If a SF
performs re-classification that results in a change of service
path, it MUST remove the existing NSH and MUST imposes a new NSH
with the base header reflecting the new path.
2. Select service path: The base header provides service chain
information and is used by SFFs to determine correct service path
selection. SFFs MUST use the base header for selecting the next
service in the service path.
3. Update a service header: NSH aware service functions MUST
decrement the service index. A service index = 0 indicates that
a packet MUST be dropped by the SFF performing NSH based
forwarding.
Service functions MAY update context headers if new/updated
context is available.
If an NSH proxy is in use (acting on behalf of a non-aware
service function for NSH actions), then the proxy MUST update
service index and MAY update contexts.
4. Service policy selection: Service function instances derive
policy selection from the service header. Context shared in the
service header can provide a range of service-relevant
information such as traffic classification. Service functions
SHOULD use NSH to select local service policy.
3.2. NSH Encapsulation
Once NSH is added to a packet, an outer encapsulation is used to
forward the original packet and the associated metadata to the start
of a service chain. The encapsulation serves two purposes:
1. Creates a topologically independent services plane. Packets are
forwarded to the required services without changing the
underlying network topology.
2. Transit network nodes simply forward the encapsulated packets as
is.
The service header is independent of the encapsulation used and is
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encapsulated in existing transports. The presence of NSH is
indicated via protocol type or other indicator in the outer
encapsulation.
See section 4 for an example using GRE and NSH encapsulation.
3.3. NSH Usage
NSH creates a dedicated service plane, that addresses many of the
limitations highlighted in section 2.2. More specifically, NSH
enables:
1. Topological Independence: Service forwarding occurs within the
service plane, via a network overlay, the underlying network
topology does not require modification. Service functions have
one or more network locators (e.g. IP address), to receive/send
data within the service plane, the NSH header contains an
identifier that is used to uniquely identify a service path and
the services within that path.
2. Service Chaining: NSH contains path identification information
needed to realize a service path (see section 4 for header
specifics). Furthermore, NSH provides the ability to monitor and
troubleshoot a service chain, end-to-end via service-specific OAM
messages. The NSH fields can be used by administrators (via, for
example a traffic analyzer) to verify (account, ensure correct
chaining, provide reports, etc.) the path specifics of packets
being forwarded along a service path.
3. Metadata Sharing: NSH provides a mechanism to carry shared
metadata between network devices and service function, and
between service functions. The semantics of the shared metadata
is communicated via a control plane to participating nodes.
Examples of metadata include classification information used for
policy enforcement and network context for forwarding post
service delivery.
4. Transport Agnostic: NSH is transport independent and can be used
with overlay and underlay forwarding topologies.
3.4. NSH Proxy Nodes
In order to support NSH unaware service functions, an NSH proxy is
used. The proxy node removes the NSH header and delivers, to the
service node, the original packet/frame via a local attachment
circuit. Examples of a local attachment circuit include, but are not
limited to: VLANs, IP in IP, GRE, VXLAN. When complete, the service
function returns the packet to the NSH-proxy via the same or
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different attachment circuit.
NSH is re-imposed on packets returned to the proxy from the non-NSH
aware service.
Typically, a SFCNF will act as a NSH-proxy when required.
An NSH proxy MUST perform NSH actions as described in section 3.1.
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4. Header Format
Base Service Header:
0 1 2 3
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|O|C|R|R|R|R|R|R| Reserved | Protocol Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service path | Service index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags: 8
Reserved: 8
Protocol Type (PT): 16
Service path (SP): 24
Service index (SI): 8
Figure 2: NSH Base Header
Base Header Field Descriptions
O bit: Indicates that this packet is an operations and management
(OAM) packet. SFF and SFs nodes MUST examine the payload and take
appropriate action (i.e. return status information).
OAM message specifics and handling details are outside the scope of
this document.
C bit: Context headers MUST be present. When C is set, one or more
contexts are in use (i.e. a value placed in a context is
significant). The C bit specifies that their ordering and sizing is
as per figure 4: network platform (32 bits), network shared (32
bits), service platform (32 bits), service shared (32 bits).
A C bit equal to zero indicates that no contexts are in use (although
they MUST be present to ensure a fixed size header) and that they can
be ignored.
If a context header is not in use, the value of that context header
MUST be zero.
All other flag fields are reserved.
Protocol type: indicates the protocol type of the original packet or
frame as per [ETYPES]
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Service Index (SI): provides location within the service path.
Service index MUST be decremented by service functions or proxy nodes
after performing required services. MAY be used in conjunction with
service path for path selection. Service Index is also valuable when
troubleshooting/reporting service paths. In addition to location
within a path, SI can be used for loop detection.
Service Path: identifies a service path. Participating nodes MUST
use this identifier for path selection. An administrator can use the
service path value for reporting and troubleshooting packets along a
specific path.
Context Headers:
0 1 2 3
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Context data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Context Data
0 1 2 3
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Platform Context |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Shared Context |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Platform Context |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Shared Context |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Context Data Significance
The following examples of context header allocation are guidelines
that illustrate how various forms of information can carried and
exchanged via NSH.
Network platform context: provides platform-specific metadata shared
between network nodes. Examples include (but are not limited to)
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ingress port information, forwarding context and encapsulation type.
Network shared context: metadata relevant to any network node such as
the result of edge classification. For example, application
information, identity information or tenancy information can be
shared using this context header.
Service platform context: provides service platform specific metadata
shared between service functions. This context header is analogous
to the network platform context, enabling service platforms to
exchange platform-centric information such as an identifier used for
load balancing decisions.
Service shared context: metadata relevant to, and shared, between
service functions. As with the shared network context,
classification information such as application type can be conveyed
using this context.
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5. NSH Example: GRE
IP Packet:
+----------+--------------------+--------------------+
|L2 header | L3 header, proto=47|GRE header,PT=0x894F|
+----------+--------------------+--------------------+
--------------+----------------+
NSH, PT=0x800 |original packet |
--------------+----------------+
L2 Frame:
+----------+--------------------+---------------------+
|L2 header | L3 header, proto=47|GRE header, PT=0x894F|
+----------+--------------------+---------------------+
---------------+---------------+
NSH, PT=0x6558 |original frame |
---------------+---------------+
Figure 5: GRE + NSH
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6. Security Considerations
As with many other protocols, NSH data can be spoofed or otherwise
modified. In many deployments, NSH will be used in a controlled
environment, with trusted devices (e.g. a data center) thus
mitigating the risk of unauthorized header manipulation.
NSH is always encapsulated in a transport protocol and therefore,
when required, existing security protocols that provide authenticity
(e.g. RFC 2119 [RFC6071]) can be used.
Similarly if confidentiality is required, existing encryption
protocols can be used in conjunction with encapsulated NSH.
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7. Acknowledgments
The authors would like to thank Nagaraj Bagepalli, Abhijit Patra,
Carlos Pignataro, Ron Parker, Peter Bosch, Tom Nadeau, Darrel Lewis,
Pritesh Kothari and Ken Gray for their detailed review, comments and
contributions.
A special thank you goes to David Ward and Tom Edsall for their
guidance and feedback.
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8. IANA Considerations
An IEEE EtherType, 0x894F, has been allocated for NSH.
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9. References
9.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[ETYPES] The IEEE Registration Authority, "IEEE 802 Numbers", 2012,
<http://www.iana.org/assignments/ieee-802-numbers/
ieee-802-numbers.xml>.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
[RFC6071] Frankel, S. and S. Krishnan, "IP Security (IPsec) and
Internet Key Exchange (IKE) Document Roadmap", RFC 6071,
February 2011.
[SFC-PS] Quinn, P., Ed. and T. Nadeau, Ed., "Service Function
Chaining Problem Statement", 2014, <http://
datatracker.ietf.org/doc/
draft-ietf-sfc-problem-statement/>.
[SFC-arch]
Quinn, P., Ed. and A. Beliveau, Ed., "Service Function
Chaining (SFC) Architecture", 2014,
<http://datatracker.ietf.org/doc/draft-quinn-sfc-arch>.
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Authors' Addresses
Paul Quinn
Cisco Systems, Inc.
Email: paulq@cisco.com
Jim Guichard
Cisco Systems, Inc.
Email: jguichar@cisco.com
Rex Fernando
Cisco Systems, Inc.
Email: rex@cisco.com
Surendra Kumar
Cisco Systems, Inc.
Email: smkumar@cisco.com
Michael Smith
Cisco Systems, Inc.
Email: michsmit@cisco.com
Navindra Yadav
Cisco Systems, Inc.
Email: nyadav@cisco.com
Puneet Agarwal
Broadcom
Email: pagarwal@broadcom.com
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Rajeev Manur
Broadcom
Email: rmanur@broadcom.com
Abhishek Chauhan
Citrix
Email: Abhishek.Chauhan@citrix.com
Brad McConnell
Rackspace
Email: bmcconne@rackspace.com
Chris Wright
Red Hat Inc.
Email: chrisw@redhat.com
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