Internet DRAFT - draft-aldrin-sfc-oam-framework
draft-aldrin-sfc-oam-framework
Internet Engineering Task Force S. Aldrin
Internet-Draft Google
Intended status: Informational R. Krishnan
Expires: January 22, 2016 Dell
N. Akiya
Big Switch
C. Pignataro
Cisco Systems
A. Ghanwani
Dell
July 23, 2015
Service Function Chaining
Operation, Administration and Maintenance Framework
draft-aldrin-sfc-oam-framework-02
Abstract
This document provides reference framework for Operations,
Administration and Maintenance (OAM) for Service Function
Chaining (SFC).
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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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 January 2016.
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document authors. All rights reserved.
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include Simplified BSD License text as described in Section 4.e of
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Table of Contents
1. Introduction
Service Function Chaining (SFC) enables the creation of composite
services that consist of an ordered set of Service Functions (SF)
that are be applied to packets and/or frames selected as a result of
classification. SFC 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. The foundations of SFC are described in the following
documents:
o SFC problem statement [I-D.ietf-sfc-problem-statement]
o SFC architecture [I-D.ietf-sfc-archiecture]
The reader is assumed to familiar with the material in these drafts.
This document provides reference framework for Operations,
Administration and Maintenance (OAM, [RFC6291]) of SFC.
Specifically, this document provides:
o In Section 2, an SFC layering model;
o In Section 3, aspects monitored by SFC OAM;
o In Section 4, functional requirements for SFC OAM;
o In Section 5, a gap analysis for SFC OAM.
1.1. Document Scope
The focus of this document is to provide an architectural framework
for SFC OAM, particularly focused on the aspect of the Operations
component within 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 which SFC operates and the underlying
Network, Transport, Link, etc., layers.
o The service layer, refered to as the "Service Layer" in Figure 1,
consists of classifiers and SFs, and uses the
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transport network, which could be an overlay network, from a
classifier to SF and from one SF to the next.
o The network overlay transport layer, refer to as the "Network",
"Transport" and layers below in Figure 1, extends between the
various SFs and is mostly transparent to the SFs themselves. It
can leverage various overlay network technologies
interconnecting SFs and allows establishment of
service function paths (SFPs).
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.).
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. Aspects Monitored by SFC OAM?
SFC operates at the service layer. For the purpose of defining
the OAM framework, the following aspects of the SFC must be capable of
monitored.
1. Service function:
SFs may be SFC-aware or SFC-unaware. An SFC-aware SF is one that
understands the SFC encapsulation has the SFF component co-resident with
the SF sub-component . An SFC-unware SF is one that does not understand
the SFC encapsulation (i.e. a legacy SF) and has to be accessed via an
separate SFF and potentially an SFC proxy function.
In both cases, an SF is accessed through an SFF in the SFC
architecture. SFC OAM must be able to monitor the SFF associated
with a given SF.
2. Service function path:
The SFP comprises a set of SFs that may be ordered or unordered.
SFC OAM must be capable of monitoring the SFP and the rendered
service path (RSP) that may be used by specific packets.
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3. Classifier:
The classifier determines which packets are mapped to an SFP.
SFC OAM must be able to monitor the operation of the classifiers.
The figure below illustrates the various aspects monitored by SFC OAM.
+-SFC +-SFC OAM
| OAM |
| | _________________________________________
| \ /\ Service Function Chain \
| +------+ \/ \ +---+ +---+ +---+ +---+ +---+ \
+----> |Classi|...(+-> ) |SF1|---|SF2|---|SF4|---|SF6|---|SF7| )
|fier | \ / +-^-+ +---+ +-|-+ +-^-+ +---+ /
+----|-+ \/_____|_______________|_______|_________ /
| | +-SFCOAM+
+----SFCOAM----+ +---+ +---+
+SFCOAM>|SF3| |SF5|
| +-^-+ +-^-+
+------|---+ | |
|Controller| +-SFCOAM+
+----------+
Service Function OAM (SFCOAM)
Figure 2: Aspects monitored by SFC OAM
3.1. Operation and Performance of SFs
3.1.1. Monitoring SF Operation
One SFC OAM requirement for the SF component is to
allow an SFC aware network device to monitor a
specific SF. This is accomplished by monitoring the SFF that
the SF is attached to.
A generalized way to monitor the operation of an SF is beyond the scope
of SFC OAM, because the functions provided by the SF are not covered by
SFC. SFs typically provide their own tools for monitoring.
An optional capability may be provided for an SFF to monitor the
operation of its attached SFs and report that on behalf of the SFs.
3.1.2. Service Function Performance Measurement
A second SFC OAM requirement for SF is to
allow an SFC aware network device to check the loss and delay to a
specific SF, located on the same or different network
devices.
3.2. Operation and Performance of SFPs
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3.2.1. Monitoring SFP Operation
SFC OAM must be capable of monitoring one or more SFPs or RSPs that are
used to realize the SFC and reporting on connectivity and providing fault
isolation.
In order to perform service connectivity verification of an SFP, the
OAM tools could be initiated from any SFC-aware network device for
end-to-end paths, or partial paths terminating on a specific SF, within
the SFP. This OAM function is to ensure the SF's chained together has
connectivity as it was intended to when SFP was established.
Necessary return code(s) 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 (e.g. multiple
SFPs, or multiple RSPs), there must be an ability to discover and
traverse all available paths.
3.2.2. Service Function Chain Performance Measurement
The ingress of the SFC or an SFC-aware network
device must have an ability to perform loss and delay measurements
over the SFC as a unit (i.e. end-to-end) or to a
specific SF through the SFC.
3.3. Monitoring the Classifier
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. 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 the various aspects monitored by SFC OAM. 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 that the SFs are
operational. 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 SFC component. OAM
messages MAY be encapsulated with necessary SFC
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header and with OAM markings when testing the SF
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.
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 the operator to monitor the network device and to
quickly detect failures such as link failures, network failures,
SF outages or SFC 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. Mechanisms must be provided so
that the SFC OAM messages may be sent along the same path that a
given data packet would follow. 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.
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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 should provide the ability to test the 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.
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
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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Table 1: OAM Tool GAP Analysis
+----------------+--------------+-------------+--------+------------+
| Layer | Connectivity | Continuity | Trace | Performance|
+----------------+--------------+-------------+--------+------------+
| N/W Overlay | Ping | BFD, NVo3 | Trace | IPPM |
+----------------+--------------+-------------+--------+------------+
| SF | None + None + None + None |
+----------------+--------------+-------------+--------+------------+
| SFC | None + None + None + None |
+----------------+--------------+-------------+--------+------------+
5.2. Missing OAM Functions
As shown in Table 1, OAM functions for SFC are not yet standardized.
Hence, there are no standards-based tools available to monitor the
various components identified in Section 3.
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.
SFC OAM must provide tools that operate through various types of
SFs including:
o Transparent SFs: These SFs typically do not make any
modifications to the packet. In such cases, the SFF may be able
to process OAM messages.
o SFs that modify the packet: These SFs modify packet
fields. Certain SFs may modify only the headers
corresponding to the network over which it is transported, e.g.
the MAC headers or overlay headers. In other cases, the IP header
of the application's packet may be modified, e.g. NAT. In yet
other cases, the application session itself may be terminated and
a new session initiated, e.g. a load balancer that offers HTTPS
termination.
6. Open Issues
- Add more details on performance measurement.
- Call out which OAM functions can be achieved by protocol design vs
requiring synthetic traffic.
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7. Security Considerations
SFC OAM must provide mechanisms for:
o Preventing usage of OAM channel for DDOS attacks.
o Preventing leakage of OAM packets meant for a given SFC beyond
that SFC.
o Preventing leakage of information about an sFC beyond its
administrative domain.
7. IANA Considerations
No action is required by IANA for this document.
8. Acknowledgements
TBD
9. Contributing Authors
Pedro A. Aranda Gutierrez
Telefonica I+D
Email: pedroa.aranda@tid.es
Diego Lopez
Telefonica I+D
Email: diego@tid.es
Joel Halpern
Ericsson
Email: joel.halpern@ericsson.com
Sriganesh Kini
Ericsson
Email: sriganesh.kini@ericsson.com
Andy Reid
BT
Email: andy.bd.reid@bt.com
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[I-D.ietf-sfc-problem-statement]
Quinn, P. and T. Nadeau, "Service Function Chaining
Problem Statement", draft-ietf-sfc-problem-statement-10
(work in progress), August 2014.
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[I-D.ietf-sfc-architecture]
Halpern J. and C. Pignataro, "Service Function Chaining
(SFC) Architecture", draft-ietf-sfc-architecture-09
(work in progress), June 2015.
10.2. Informative References
[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
Google
Email: aldrin.ietf@gmail.com
Ram Krishnan
Dell
Email: ramkri123@gmail.com
Nobo Akiya
Big Switch
Email: nobo.akiya.dev@gmail.com
Carlos Pignataro
Cisco Systems
Email: cpignata@cisco.com
Anoop Ghanwani
Dell
Email: anoop@alumni.duke.edu
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