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draft-ietf-sfc-oam-framework
Internet Engineering Task Force S. Aldrin
Internet-Draft Huawei Technologies
Intended status: Informational C. Pignataro
Expires: January 3, 2015 N. Akiya
Cisco Systems
July 2, 2014
Service Function Chaining
Operations, Administration and Maintenance Framework
draft-aldrin-sfc-oam-framework-00
Abstract
This document provides reference framework for Operations,
Administration and Maintenance (OAM) of Service Function Chaining
(SFC).
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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This Internet-Draft will expire on December 30, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Document Scope . . . . . . . . . . . . . . . . . . . . . . 3
2. SFC Layering Model . . . . . . . . . . . . . . . . . . . . . . 3
3. SFC OAM Components . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Service Function Component . . . . . . . . . . . . . . . . 5
3.1.1. Service Function Availability . . . . . . . . . . . . 5
3.1.2. Service Function Performance Measurement . . . . . . . 6
3.2. Service Function Chain Component . . . . . . . . . . . . . 6
3.2.1. Service Function Chain Availability . . . . . . . . . 6
3.2.2. Service Function Chain Performance Measurement . . . . 6
3.3. Classifier Component . . . . . . . . . . . . . . . . . . . 7
4. SFC OAM Functions . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Connectivity Functions . . . . . . . . . . . . . . . . . . 7
4.2. Continuity Functions . . . . . . . . . . . . . . . . . . . 8
4.3. Trace Functions . . . . . . . . . . . . . . . . . . . . . 8
4.4. Performance Measurement Function . . . . . . . . . . . . . 8
5. Gap Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Existing OAM Functions . . . . . . . . . . . . . . . . . . 9
5.2. Missing OAM Functions . . . . . . . . . . . . . . . . . . 10
5.3. Required OAM Functions . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Service Function Chaining (SFC) enables the creation of composite
services that consist of an ordered set of Service Functions (SF)
that must be applied to packets and/or frames selected as a result of
classification. Service Function Chaining is a concept that provides
for more than just the application of an ordered set of SFs to
selected traffic; rather, it describes a method for deploying SFs in
a way that enables dynamic ordering and topological independence of
those SFs as well as the exchange of metadata between participating
entities. Foundations of the SFC are described in below documents:
o [I-D.ietf-sfc-problem-statement]: SFC problem statement.
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o Various individual drafts
This document provides reference framework for Operations,
Administration and Maintenance (OAM, [RFC6291]) of the SFC.
Specifically, this document provides:
o In Section 2, an SFC layering model;
o In Section 3, involved components within the SFC layer;
o In Section 4, functional requirements for the SFC OAM;
o In Section 5, an OAM gap analysis.
1.1. Document Scope
The focus of this document is to provide an architectural framework
for the SFC OAM, particularly focused on the aspect of the Operation
portion of the OAM. Actual solutions and mechanisms are outside the
scope of this document.
2. SFC Layering Model
Multiple layers come into play for implementing the SFC. These
include the service layer at SFC layer and the underlying Network,
Transport, Link, etc., layers.
o The service layer, refer to as the "Service Layer" in Figure 1,
consists of classifiers and service functions, and uses the
overlay network reach from a classifier to service functions and
service functions to service functions.
o The network overlay transport layer, refer to as the "Network",
"transport" and layers below in Figure 1, extends in between
various service functions and is mostly transparent to the service
functions. It leverages various overlay network technologies
interconnecting service functions and allows establishing of
service function paths.
o The link layer, refer to as the "Link" in Figure 1, is dependent
upon the physical technology used. Ethernet is a popular choice
for this layer, but other alternatives are deployed (e.g. POS,
DWDM etc...).
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o----------------------Service Layer----------------------o
+------+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
|Classi|---|SF1|---|SF2|---|SF3|---|SF4|---|SF5|---|SF6|---|SF7|
|fier | +---+ +---+ +---+ +---+ +---+ +---+ +---+
+------+
o-N/W Elem 1----o o-N/w Elem 2-o o-N/W Elem 3-o
o-----------------o-------------------o---------------o Network
o-----------------o-----------------------------------o Transport
o--------o--------o--------o--------o--------o--------o Link
Figure 1: SFC Layering Example
3. SFC OAM Components
The SFC operates at the service layer. For the purpose of defining
the OAM framework, the service layer is broken up into three distinct
components.
1. Service function component: A function providing a specific
service. OAM solutions for this component are to test the
service functions from any SFC aware network devices (i.e.
classifiers, controllers, other service nodes).
2. Service function chain component: An ordered set of service
functions. OAM solution for this component are to test the
service function chains and the service function paths.
3. Classifier component: A policy that describes the mapping from
flows to service function chains. OAM solutions for this
component are to test the validity of the classifiers.
Below figure illustrates an example where OAM for the three defined
components are used within the SFC environment.
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+-Classifier +-Service Function Chain OAM
| OAM |
| | _________________________________________
| \ /\ Service Function Chain \
| +------+ \/ \ +---+ +---+ +---+ +---+ +---+ \
+----> |Classi|...(+-> ) |SF1|---|SF2|---|SF4|---|SF6|---|SF7| )
|fier | \ / +-^-+ +---+ +-|-+ +-^-+ +---+ /
+----|-+ \/_____|_______________|_______|_________ /
| | +-SF_OAM+
+----SF_OAM----+ +---+ +---+
+SF_OAM>|SF3| |SF5|
| +-^-+ +-^-+
+------|---+ | |
|Controller| +-SF_OAM+
+----------+
Service Function OAM (SF_OAM)
Figure 2: SFC OAM for Three Components
It is expected that multiple SFC OAM solutions will be defined, many
targeting one specific component of the service layer. However, it
is critical that SFC OAM solutions together provide the coverage of
all three SFC OAM components: the service function component, the
service function chain component and the classifier component.
3.1. Service Function Component
3.1.1. Service Function Availability
One SFC OAM requirement for the service function component is to
allow an SFC aware network device to check the availability to a
specific service function, located on the same or different network
devices. Service function availability is an aspect which raises an
interesting question. How does one determine that a service function
is available? On one end of the spectrum, one might argue that a
service function is sufficiently available if the service node
(physical or virtual) hosting the service function is available and
is functional. On the other end of the spectrum, one might argue
that the service function availability can only be concluded if the
packet, after passing through the service function, was examined and
verified that the packet got expected service applied.
The former approach will likely not provide sufficient confidence to
the actual service function availability, i.e. a service node and a
service function are two different entities. The latter approach is
capable of providing an extensive verification, but comes with a
cost. Some service functions make direct modifications to packets,
while other service functions do not make any modifications to
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packets. Additionally, purpose of some service functions is to,
conditionally, drop packets intentionally. In such case, packets
will not be coming out from the service function. The fact is that
there are many flavors of service functions available, and many more
flavors of service functions will likely be introduced in future.
Even a given service function may introduce a new functionality
within a service function (ex: a new signature in a firewall). The
cost of this approach is that verifier functions will need to be
continuously modified to "keep up" with new services coming out: lack
of extendibility.
This framework document provides a RECOMMENDED architectural model
where generalized approach is taken to verify that a service function
is sufficiently available. TBD - details will be provided in a later
revision.
3.1.2. Service Function Performance Measurement
Second SFC OAM requirement for the service function component is to
allow an SFC aware network device to check the loss and delay of a
specific service function, located on the same or different network
devices. TBD - details will be provided in a later revision.
3.2. Service Function Chain Component
3.2.1. Service Function Chain Availability
Verifying an SFC is a complicated process as the SFC could be
comprised of varying SF's. Thus, SFC requires the OAM layer to
perform validation and verification of SF's within an SFC Path, as
well as connectivity and fault isolation.
In order to perform service connectivity verification of an SFC, the
OAM could be initiated from any SFC aware network devices for end-to-
end paths or partial path terminating on a specific SF within the
SFC. This OAM function is to ensure the SF's chained together has
connectivity as it is intended to when SFC was established. Necessary
return code should be defined to be sent back in the response to OAM
packet, in order to qualify the verification.
When ECMP exists at the service layer on a given SFC, there must be
an ability to discover and traverse all available paths.
TBD - further details will be provided in a later revision.
3.2.2. Service Function Chain Performance Measurement
The ingress of the service function chain or an SFC aware network
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device must have an ability to perform loss and delay measurements
over the service function chain as a unit (i.e. end-to-end) or to a
specific service function through the SFC.
3.3. Classifier Component
A classifier defines a flow and maps incoming traffic to a specific
SFC, and it is vital that the classifier is correctly defined and
functioning. The SFC OAM must be able to test the definition of
flows and the mapping functionality to expected SFCs.
4. SFC OAM Functions
Section 3 described SFC OAM operations required on each SFC
component. This section explores the same from the OAM functionality
point of view, which many will be applicable to multiple SFC
components.
Various SFC OAM requirements provides the need for various OAM
functions at different layers. Many of the OAM functions at
different layers are already defined and in existence. In order to
support SFC and SF's, these functions have to be enhanced to operate
a single SF to multiple SF's in an SFC and also multiple SFC's.
4.1. Connectivity Functions
Connectivity is mainly an on-demand function to verify that the
connectivity exists between network elements and the availability
exists to service functions. Ping is a common tool used to perform
this function. OAM messages should be encapsulated with necessary
SFC header and with OAM markings when testing the service function
chain component. OAM messages MAY be encapsulated with necessary SFC
header and with OAM markings when testing the service function
component. Some of the OAM functions performed by connectivity
functions are as follows:
o Verify the MTU size from a source to the destination SF or through
the SFC. This requires the ability for OAM packet to take
variable length packet size.
o Verify the packet re-ordering and corruption.
o Verify the policy of an SFC or SF using OAM packet.
o Verification and validating forwarding paths.
o Proactively test alternate or protected paths to ensure
reliability of network configurations.
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4.2. Continuity Functions
Continuity is a model where OAM messages are sent periodically to
validate or verify the reachability to a given SF or through a given
SFC. This allows monitor network device to quickly detect failures
like link failures, network failures, service function outages or
service function chain outages. BFD is one such function which helps
in detecting failures quickly. OAM functions supported by continuity
check are as follows:
o Ability to provision continuity check to a given SF or through a
given SFC.
o Notifying the failure upon failure detection for other OAM
functions to take appropriate action.
4.3. Trace Functions
Tracing is an important OAM function that allows the operation to
trigger an action (ex: response generation) from every transit device
on the tested layer. This function is typically useful to gather
information from every transit devices or to isolate the failure
point towards an SF or through an SFC. Some of the OAM functions
supported by trace functions are:
o Ability to trigger action from every transit device on the tested
layer towards an SF or through an SFC, using TTL or other means.
o Ability to trigger every transit device to generate response with
OAM code(s) on the tested layer towards an SF or through an SFC,
using TTL or other means.
o Ability to discover and traverse ECMP paths within an SFC.
o Ability to skip un-supported SF's while tracing SF's in an SFC.
4.4. Performance Measurement Function
Performance management functions involve measuring of packet loss,
delay, delay variance, etc. These measurements could be measured
pro-actively and on-demand.
SFC OAM framework should provide the ability to perform packet loss
for an SFC. In an SFC, there are various SF's chained together.
Measuring packet loss is very important function. Using on-demand
function, the packet loss could be measured using statistical means.
Using OAM packets, the approximation of packet loss for a given SFC
could be measured.
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Delay within an SFC could be measured from the time it takes for a
packet to traverse the SFC from ingress SF to egress SF. As the
SFC's are generally unidirectional in nature, measurement of one-way
delay is important. In order to measure one-way delay, the clocks
have to be synchronized using NTP, GPS, etc.
Delay variance could also be measured by sending OAM packets and
measuring the jitter between the packets passing through the SFC.
Some of the OAM functions supported by the performance measurement
functions are:
o Ability to measure the packet processing delay of a service
function or a service function path along an SFC.
o Ability to measure the packet loss of a service function or a
service function path along an SFC.
5. Gap Analysis
This Section identifies various OAM functions available at different
levels. It will also identify various gaps, if not all, existing
within the existing toolset, to perform OAM function on an SFC.
5.1. Existing OAM Functions
There are various OAM tool sets available to perform OAM function and
network layer, protocol layers and link layers. These OAM functions
could validate some of the network overlay transport. Tools like
ping and trace are in existence to perform connectivity check and
tracing intermediate hops in a network. These tools support
different network types like IP, MPLS, TRILL etc. There is also an
effort to extend the tool set to provide connectivity and continuity
checks within overlay networks. BFD is another tool which helps in
detection of data forwarding failures.
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+----------------+--------------+-------------+--------+------------+
| Layer | Connectivity | Continuity | Trace | Performance|
+----------------+--------------+-------------+--------+------------+
| N/W Overlay | Ping | BFD, NVo3 | Trace | IPPM |
+----------------+--------------+-------------+--------+------------+
| SF | None + None + None + None |
+----------------+--------------+-------------+--------+------------+
| SFC | None + None + None + None |
+----------------+--------------+-------------+--------+------------+
Figure 3: OAM Tool GAP Analysis
5.2. Missing OAM Functions
As shown in Figure 3, OAM functions for SFC are not standardized yet.
Hence, there are no standard based tools available to verify SF and
SFC.
5.3. Required OAM Functions
Primary OAM functions exist for network, transport, link and other
layers. Tools like ping, trace, BFD, etc., exist in order to perform
these OAM functions. Configuration, orchestration and manageability
of SF and SFC could be performed using CLI, Netconf etc.
For configuration, manageability and orchestration, providing data
and information models for SFC is very much essential. With
virtualized SF and SFC, manageability of these functions has to be
done programmatically.
6. Security Considerations
SFC and SF OAM must provide mechanisms for:
o Preventing usage of OAM channel for DDOS attacks.
o OAM packets meant for a given SFC should not get leaked beyond
that SFC.
o Prevent OAM packets to leak the information of an SFC beyond its
administrative domain.
7. IANA Considerations
No action is required by IANA for this document.
8. Acknowledgements
TBD
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9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[I-D.ietf-sfc-problem-statement]
Quinn, P. and T. Nadeau, "Service Function Chaining
Problem Statement", draft-ietf-sfc-problem-statement-07
(work in progress), June 2014.
[RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
D., and S. Mansfield, "Guidelines for the Use of the "OAM"
Acronym in the IETF", BCP 161, RFC 6291, June 2011.
Authors' Addresses
Sam K. Aldrin
Huawei Technologies
Email: aldrin.ietf@gmail.com
Carlos Pignataro
Cisco Systems
Email: cpignata@cisco.com
Nobo Akiya
Cisco Systems
Email: nobo@cisco.com
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