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Keywords: SFC, OAM, Framework

Internet Engineering Task Force (IETF) S. Aldrin
Request for Comments: 8924 Google
Category: Informational C. Pignataro, Ed.
ISSN: 2070-1721 N. Kumar, Ed.
Cisco
R. Krishnan
VMware
A. Ghanwani
Dell
October 2020
Service Function Chaining (SFC) Operations, Administration, and
Maintenance (OAM) Framework
Abstract
This document provides a reference framework for Operations,
Administration, and Maintenance (OAM) for Service Function Chaining
(SFC).
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8924.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction
1.1. Document Scope
1.2. Acronyms and Terminology
1.2.1. Acronyms
1.2.2. Terminology
2. SFC Layering Model
3. SFC OAM Components
3.1. The SF Component
3.1.1. SF Availability
3.1.2. SF Performance Measurement
3.2. The SFC Component
3.2.1. SFC Availability
3.2.2. SFC Performance Measurement
3.3. Classifier Component
3.4. Underlay Network
3.5. Overlay Network
4. SFC OAM Functions
4.1. Connectivity Functions
4.2. Continuity Functions
4.3. Trace Functions
4.4. Performance Measurement Functions
5. Gap Analysis
5.1. Existing OAM Functions
5.2. Missing OAM Functions
5.3. Required OAM Functions
6. Operational Aspects of SFC OAM at the Service Layer
6.1. SFC OAM Packet Marker
6.2. OAM Packet Processing and Forwarding Semantic
6.3. OAM Function Types
7. Candidate SFC OAM Tools
7.1. ICMP
7.2. BFD / Seamless BFD
7.3. In Situ OAM
7.4. SFC Traceroute
8. Manageability Considerations
9. Security Considerations
10. IANA Considerations
11. Informative References
Acknowledgements
Contributors
Authors' Addresses
1. Introduction
Service Function Chaining (SFC) enables the creation of composite
services that consist of an ordered set of Service Functions (SFs)
that are to be applied to any traffic selected as a result of
classification [RFC7665]. 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:
* SFC Problem Statement [RFC7498]
* SFC Architecture [RFC7665]
The reader is assumed to be familiar with the material in [RFC7665].
This document provides a reference framework for Operations,
Administration, and Maintenance (OAM) [RFC6291] of SFC.
Specifically, this document provides:
* an SFC layering model (Section 2),
* aspects monitored by SFC OAM (Section 3),
* functional requirements for SFC OAM (Section 4),
* a gap analysis for SFC OAM (Section 5),
* operational aspects of SFC OAM at the service layer (Section 6),
* applicability of various OAM tools (Section 7), and
* manageability considerations for SF and SFC (Section 8).
SFC OAM solution documents should refer to this document to indicate
the SFC OAM component and the functionality they target.
OAM controllers are SFC-aware network devices that are capable of
generating OAM packets. They should be within the same
administrative domain as the target SFC-enabled domain.
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.
1.2. Acronyms and Terminology
1.2.1. Acronyms
BFD Bidirectional Forwarding Detection
CLI Command-Line Interface
DWDM Dense Wavelength Division Multiplexing
E-OAM Ethernet OAM
hSFC Hierarchical Service Function Chaining
IBN Internal Boundary Node
IPPM IP Performance Metrics
MPLS Multiprotocol Label Switching
MPLS_PM MPLS Performance Measurement
NETCONF Network Configuration Protocol
NSH Network Service Header
NVO3 Network Virtualization over Layer 3
OAM Operations, Administration, and Maintenance
POS Packet over SONET
RSP Rendered Service Path
SF Service Function
SFC Service Function Chain
SFF Service Function Forwarder
SFP Service Function Path
SNMP Simple Network Management Protocol
TRILL Transparent Interconnection of Lots of Links
VM Virtual Machine
1.2.2. Terminology
This document uses the terminology defined in [RFC7665] and
[RFC8300], and readers are expected to be familiar with it.
2. SFC Layering Model
Multiple layers come into play for implementing the SFC. These
include the service layer and the underlying layers (network layer,
link layer, etc.).
* The service layer consists of SFC data-plane elements that include
classifiers, Service Functions (SFs), Service Function Forwarders
(SFF), and SFC Proxies. This layer uses the overlay network layer
for ensuring connectivity between SFC data-plane elements.
* The overlay network layer leverages various overlay network
technologies (e.g., Virtual eXtensible Local Area Network (VXLAN))
for interconnecting SFC data-plane elements and allows
establishing Service Function Paths (SFPs). This layer is mostly
transparent to the SFC data-plane elements, as not all the data-
plane elements process the overlay header.
* The underlay network layer is dictated by the networking
technology deployed within a network (e.g., IP, MPLS).
* The link layer is tightly coupled with the physical technology
used. Ethernet is one such choice for this layer, but other
alternatives may be deployed (e.g., POS and DWDM). In a virtual
environment, virtualized I/O technologies, such as Single Root I/O
Virtualization (SR-IOV) or similar, are also applicable for this
layer. The same or distinct link layer technologies may be used
in each leg shown in Figure 1.
o----------------------Service Layer----------------------o
+------+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
|Classi|---|SF1|---|SF2|---|SF3|---|SF4|---|SF5|---|SF6|---|SF7|
|fier | +---+ +---+ +---+ +---+ +---+ +---+ +---+
+------+
<------VM1------> <--VM2--> <--VM3-->
^-----------------^-------------------^---------------^ Overlay
Network
o-----------------o-------------------o---------------o Underlay
Network
o--------o--------o--------o----------o-------o-------o Link
Figure 1: SFC Layering Example
In Figure 1, the service-layer elements, such as classifier and SF,
are depicted as virtual entities that are interconnected using an
overlay network. The underlay network may comprise multiple
intermediate nodes not shown in the figure that provide underlay
connectivity between the service-layer elements.
While Figure 1 depicts an example where SFs are enabled as virtual
entities, the SFC architecture does not make any assumptions on how
the SFC data-plane elements are deployed. The SFC architecture is
flexible and accommodates physical or virtual entity deployment. SFC
OAM accounts for this flexibility, and accordingly it is applicable
whether SFC data-plane elements are deployed directly on physical
hardware, as one or more virtual entities, or any combination
thereof.
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:
SF component:
OAM functions applicable at this component include testing the SFs
from any SFC-aware network device (e.g., classifiers, controllers,
and other service nodes). Testing an SF may be more expansive
than just checking connectivity to the SF, such as checking if the
SF is providing its intended service. Refer to Section 3.1.1 for
a more detailed discussion.
SFC component:
OAM functions applicable at this component include (but are not
limited to) testing the SFCs and the SFPs, validation of the
correlation between an SFC and the actual forwarding path followed
by a packet matching that SFC, i.e., the Rendered Service Path
(RSP). Some of the hops of an SFC may not be visible when
Hierarchical Service Function Chaining (hSFC) [RFC8459] is in use.
In such schemes, it is the responsibility of the Internal Boundary
Node (IBN) to glue the connectivity between different levels for
end-to-end OAM functionality.
Classifier component:
OAM functions applicable at this component include testing the
validity of the classification rules and detecting any incoherence
among the rules installed when more than one classifier is used,
as explained in Section 2.2 of [RFC7665].
Figure 2 illustrates an example where OAM for the three defined
components are used within the SFC environment.
+-Classifier +-Service Function Chain OAM
| OAM |
| | ___________________________________________
| \ /\ Service Function Chain \
| \ / \ +---+ +---+ +-----+ +---+ \
| \ / \ |SF1| |SF2| |Proxy|--|SF3| \
| +------+ \/ \ +---+ +---+ +-----+ +---+ \
+----> | |...(+-> ) | | | )
|Classi| \ / +-----+ +-----+ +-----+ /
|fier | \ / | SFF1|----| SFF2|----| SFF3| /
| | \ / +--^--+ +-----+ +-----+ /
+----|-+ \/_________|________________________________/
| |
+-------SF_OAM-------+
+---+ +---+
+SF_OAM>|SF3| |SF5|
| +-^-+ +-^-+
+------|---+ | |
|Controller| +-SF_OAM+
+----------+
Service Function OAM (SF_OAM)
Figure 2: SFC OAM Components
It is expected that multiple SFC OAM solutions will be defined, each
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 SF component, the SFC component,
and the classifier component.
3.1. The SF Component
3.1.1. SF Availability
One SFC OAM requirement for the SF component is to allow an SFC-aware
network device to check the availability of a specific SF (instance),
located on the same or different network device(s). For cases where
multiple instances of an SF are used to realize a given SF for the
purpose of load sharing, SF availability can be performed by checking
the availability of any one of those instances, or the availability
check may be targeted at a specific instance. SF availability is an
aspect that raises an interesting question: How does one determine
that an SF is available? At one end of the spectrum, one might argue
that an SF is sufficiently available if the service node (physical or
virtual) hosting the SF is available and is functional. At the other
end of the spectrum, one might argue that the SF's availability can
only be deduced if the packet, after passing through the SF, was
examined and it was verified that the packet did indeed get the
expected service.
The former approach will likely not provide sufficient confidence
about the actual SF availability, i.e., a service node and an SF are
two different entities. The latter approach is capable of providing
an extensive verification but comes at a cost. Some SFs make direct
modifications to packets, while others do not. Additionally, the
purpose of some SFs may be to drop certain packets intentionally. In
such cases, it is normal behavior that certain packets will not be
egressing out from the SF. The OAM mechanism needs to take into
account such SF specifics when assessing SF availability. Note that
there are many flavors of SFs available and many more that are likely
be introduced in the future. Even a given SF may introduce a new
functionality (e.g., a new signature in a firewall). The cost of
this approach is that the OAM mechanism for some SF will need to be
continuously modified in order to "keep up" with new functionality
being introduced.
The SF availability check can be performed using a generalized
approach, i.e., at an adequate granularity to provide a basic SF
service. The task of evaluating the true availability of an SF is a
complex activity, currently having no simple, unified solution.
There is currently no standard means of doing so. Any such mechanism
would be far from a typical OAM function, so it is not explored as
part of the analysis in Sections 4 and 5.
3.1.2. SF Performance Measurement
The second SFC OAM requirement for the SF component is to allow an
SFC-aware network device to check the performance metrics, such as
loss and delay induced by a specific SF for processing legitimate
traffic. Performance measurement can be passive by using live
traffic, an active measurement by using synthetic probe packets, or a
hybrid method that uses a combination of active and passive
measurement. More details about this OAM function is explained in
Section 4.4.
On the one hand, the performance of any specific SF can be quantified
by measuring the loss and delay metrics of the traffic from the SFF
to the respective SF, while on the other hand, the performance can be
measured by leveraging the loss and delay metrics from the respective
SFs. The latter requires SF involvement to perform the measurement,
while the former does not. For cases where multiple instances of an
SF are used to realize a given SF for the purpose of load sharing, SF
performance can be quantified by measuring the metrics for any one
instance of SF or by measuring the metrics for a specific instance.
The metrics measured to quantify the performance of the SF component
are not just limited to loss and delay. Other metrics, such as
throughput, also exist and the choice of metrics for performance
measurement is outside the scope of this document.
3.2. The SFC Component
3.2.1. SFC Availability
An SFC could comprise varying SFs, and so the OAM layer is required
to perform validation and verification of SFs within an SFP, in
addition to connectivity verification and fault isolation.
In order to perform service connectivity verification of an SFC/SFP,
the OAM functions could be initiated from any SFC-aware network
device of an SFC-enabled domain for end-to-end paths, or partial
paths terminating on a specific SF, within the SFC/SFP. The goal of
this OAM function is to ensure the SFs chained together have
connectivity, as was intended at the time when the SFC was
established. The necessary return codes should be defined for
sending back in the response to the OAM packet, in order to complete
the verification.
When ECMP is in use at the service layer for any given SFC, there
must be the ability to discover and traverse all available paths.
A detailed explanation of the mechanism is outside the scope of this
document and is expected to be included in the actual solution
document.
3.2.2. SFC Performance Measurement
Any SFC-aware network device should have the ability to make
performance measurements over the entire SFC (i.e., end-to-end) or on
a specific segment of SFs within the SFC.
3.3. Classifier Component
A classifier maintains the classification rules that map a flow to a
specific SFC. It is vital that the classifier is correctly
configured with updated classification rules and is functioning as
expected. The SFC OAM must be able to validate the classification
rules by assessing whether a flow is appropriately mapped to the
relevant SFC and detect any misclassification. Sample OAM packets
can be presented to the classifiers to assess the behavior with
regard to a given classification entry.
The classifier availability check may be performed to check the
availability of the classifier to apply the rules and classify the
traffic flows. Any SFC-aware network device should have the ability
to perform availability checking of the classifier component for each
SFC.
Any SFC-aware network device should have the ability to perform
performance measurement of the classifier component for each SFC.
The performance can be quantified by measuring the performance
metrics of the traffic from the classifier for each SFC/SFP.
3.4. Underlay Network
The underlay network provides connectivity between the SFC
components, so the availability or the performance of the underlay
network directly impacts the SFC OAM.
Any SFC-aware network device may have the ability to perform an
availability check or performance measurement of the underlay network
using any existing OAM functions listed in Section 5.1.
3.5. Overlay Network
The overlay network provides connectivity for the service plane
between the SFC components and is mostly transparent to the SFC data-
plane elements.
Any SFC-aware network device may have the ability to perform an
availability check or performance measurement of the overlay network
using any existing OAM functions listed in Section 5.1.
4. SFC OAM Functions
Section 3 described SFC OAM components and the associated OAM
operations on each of them. This section explores SFC OAM functions
that are applicable for more than one SFC component.
The various SFC OAM requirements listed in Section 3 highlight the
need for various OAM functions at the service layer. As listed in
Section 5.1, various OAM functions are in existence that are defined
to perform OAM functionality at different layers. In order to apply
such OAM functions at the service layer, they need to be enhanced to
operate on a single SF/SFF or multiple SFs/SFFs spanning across one
or more SFCs.
4.1. Connectivity Functions
Connectivity is mainly an on-demand function to verify that
connectivity exists between certain network elements and that the SFs
are available. For example, Label Switched Path (LSP) Ping [RFC8029]
is a common tool used to perform this function for an MPLS network.
Some of the OAM functions performed by connectivity functions are as
follows:
* Verify the Path MTU from a source to the destination SF or through
the SFC. This requires the ability for the OAM packet to be of
variable length.
* Detect any packet reordering and corruption.
* Verify that an SFC or SF is applying the expected policy.
* Verify and validate forwarding paths.
* 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 of a given SF within an SFC or
for the entire SFC. This allows a monitoring network device (such as
the classifier or controller) to quickly detect failures, such as
link failures, network element failures, SF outages, or SFC outages.
BFD [RFC5880] is one such protocol that helps in detecting failures
quickly. OAM functions supported by continuity functions are as
follows:
* Provision a continuity check to a given SF within an SFC or for
the entire SFC.
* Proactively test alternate or protected paths to ensure
reliability of network configurations.
* Notifying other OAM functions or applications of the detected
failures so they can take appropriate action.
4.3. Trace Functions
Tracing is an OAM function that allows the operation to trigger an
action (e.g., response generation) from every transit device (e.g.,
SFF, SF, and SFC Proxy) on the tested layer. This function is
typically useful for gathering information from every transit device
or for isolating the failure point to a specific SF within an SFC or
for an entire SFC. Some of the OAM functions supported by trace
functions are:
* the ability to trigger an action from every transit device at the
SFC layer, using TTL or other means,
* the ability to trigger every transit device at the SFC layer to
generate a response with OAM code(s) using TTL or other means,
* the ability to discover and traverse ECMP paths within an SFC, and
* the ability to skip SFs that do not support OAM while tracing SFs
in an SFC.
4.4. Performance Measurement Functions
Performance measurement functions involve measuring of packet loss,
delay, delay variance, etc. These performance metrics may be
measured proactively or on demand.
SFC OAM should provide the ability to measure packet loss for an SFC.
On-demand measurement can be used to estimate packet loss using
statistical methods. To ensure accurate estimations, one needs to
ensure that OAM packets are treated the same and also share the same
fate as regular data traffic.
Delay within an SFC could be measured based on the time it takes for
a packet to traverse the SFC from the ingress SFC node to the egress
SFF. Measurement protocols, such as the One-Way Active Measurement
Protocol (OWAMP) [RFC4656] and the Two-Way Active Measurement
Protocol (TWAMP) [RFC5357], can be used to measure delay
characteristics. As SFCs are unidirectional in nature, measurement
of one-way delay [RFC7679] is important. In order to measure one-way
delay, time synchronization must be supported by means such as NTP,
GPS, Precision Time Protocol (PTP), etc.
One-way delay variation [RFC3393] could also be calculated by sending
OAM packets and measuring the jitter for traffic passing through an
SFC.
Some of the OAM functions supported by the performance measurement
functions are:
* the ability to measure the packet processing delay induced by a
single SF or the one-way delay to traverse an SFP bound to a given
SFC, and
* the ability to measure the packet loss [RFC7680] within an SF or
an SFP bound to a given SFC.
5. Gap Analysis
This section identifies various OAM functions available at different
layers introduced in Section 2. It also identifies various gaps that
exist within the current toolset for performing OAM functions
required for SFC.
5.1. Existing OAM Functions
There are various OAM toolsets available to perform OAM functions
within various layers. These OAM functions may be used to validate
some of the underlay and overlay networks. Tools like ping and trace
are in existence to perform connectivity checks and trace
intermediate hops in a network. These tools support different
network types, like IP, MPLS, TRILL, etc. Ethernet OAM (E-OAM)
[Y.1731] [EFM] and Connectivity Fault Management (CFM) [DOT1Q] offer
OAM mechanisms, such as a continuity check for Ethernet links. There
is an effort around NVO3 OAM to provide connectivity and continuity
checks for networks that use NVO3. BFD is used for the detection of
data-plane forwarding failures. The IPPM framework [RFC2330] offers
tools such as OWAMP [RFC4656] and TWAMP [RFC5357] (collectively
referred to as IPPM in this section) to measure various performance
metrics. MPLS Packet Loss Measurement (LM) and Packet Delay
Measurement (DM) (collectively referred to as MPLS_PM in this
section) [RFC6374] offer the ability to measure performance metrics
in MPLS networks. There is also an effort to extend the toolset to
provide connectivity and continuity checks within overlay networks.
BFD is another tool that helps in detecting data forwarding failures.
Table 1 below is not exhaustive.
+============+==============+============+=======+=============+
| Layer | Connectivity | Continuity | Trace | Performance |
+============+==============+============+=======+=============+
| Underlay | Ping | E-OAM, BFD | Trace | IPPM, |
| network | | | | MPLS_PM |
+------------+--------------+------------+-------+-------------+
| Overlay | Ping | BFD, NVO3 | Trace | IPPM |
| network | | OAM | | |
+------------+--------------+------------+-------+-------------+
| Classifier | Ping | BFD | Trace | None |
+------------+--------------+------------+-------+-------------+
| SF | None | None | None | None |
+------------+--------------+------------+-------+-------------+
| SFC | None | None | None | None |
+------------+--------------+------------+-------+-------------+
Table 1: OAM Tool Gap Analysis
5.2. Missing OAM Functions
As shown in Table 1, there are no standards-based tools available at
the time of this writing that can be used natively (i.e., without
enhancement) for the verification of SFs and SFCs.
5.3. Required OAM Functions
Primary OAM functions exist for underlying layers. Tools like ping,
trace, BFD, etc. exist in order to perform these OAM functions.
As depicted in Table 1, toolsets and solutions are required to
perform the OAM functions at the service layer.
6. Operational Aspects of SFC OAM at the Service Layer
This section describes the operational aspects of SFC OAM at the
service layer to perform the SFC OAM function defined in Section 4
and analyzes the applicability of various existing OAM toolsets in
the service layer.
6.1. SFC OAM Packet Marker
SFC OAM messages should be encapsulated with the necessary SFC header
and with OAM markings when testing the SFC component. SFC OAM
messages may be encapsulated with the necessary SFC header and with
OAM markings when testing the SF component.
The SFC OAM function described in Section 4 performed at the service
layer or overlay network layer must mark the packet as an OAM packet
so that relevant nodes can differentiate OAM packets from data
packets. The base header defined in Section 2.2 of [RFC8300] assigns
a bit to indicate OAM packets. When NSH encapsulation is used at the
service layer, the O bit must be set to differentiate the OAM packet.
Any other overlay encapsulations used at the service layer must have
a way to mark the packet as an OAM packet.
6.2. OAM Packet Processing and Forwarding Semantic
Upon receiving an OAM packet, an SFC-aware SF may choose to discard
the packet if it does not support OAM functionality or if the local
policy prevents it from processing the OAM packet. When an SF
supports OAM functionality, it is desirable to process the packet and
provide an appropriate response to allow end-to-end verification. To
limit performance impact due to OAM, SFC-aware SFs should rate-limit
the number of OAM packets processed.
An SFF may choose to not forward the OAM packet to an SF if the SF
does not support OAM or if the policy does not allow the forwarding
of OAM packets to that SF. The SFF may choose to skip the SF, modify
the packet's header, and forward the packet to the next SFC node in
the chain. It should be noted that skipping an SF might have
implications on some OAM functions (e.g., the delay measurement may
not be accurate). The method by which an SFF detects if the
connected SF supports or is allowed to process OAM packets is outside
the scope of this document. It could be a configuration parameter
instructed by the controller, or it can be done by dynamic
negotiation between the SF and SFF.
If the SFF receiving the OAM packet bound to a given SFC is the last
SFF in the chain, it must send a relevant response to the initiator
of the OAM packet. Depending on the type of OAM solution and toolset
used, the response could be a simple response (such as ICMP reply) or
could include additional data from the received OAM packet (like
statistical data consolidated along the path). The details are
expected to be covered in the solution documents.
Any SFC-aware node that initiates an OAM packet must set the OAM
marker in the overlay encapsulation.
6.3. OAM Function Types
As described in Section 4, there are different OAM functions that may
require different OAM solutions. While the presence of the OAM
marker in the overlay header (e.g., O bit in the NSH header)
indicates it as an OAM packet, it is not sufficient to indicate what
OAM function the packet is intended for. The Next Protocol field in
the NSH header may be used to indicate what OAM function is intended
or what toolset is used. Any other overlay encapsulations used at
the service layer must have a similar way to indicate the intended
OAM function.
7. Candidate SFC OAM Tools
As described in Section 5.1, there are different toolsets available
to perform OAM functions at different layers. This section describe
the applicability of some of the available toolsets in the service
layer.
7.1. ICMP
[RFC0792] and [RFC4443] describe the use of ICMP in IPv4 and IPv6
networks respectively. It explains how ICMP messages can be used to
test the network reachability between different end points and
perform basic network diagnostics.
ICMP could be leveraged for connectivity functions (defined in
Section 4.1) to verify the availability of an SF or SFC. The
initiator can generate an ICMP echo request message and control the
service-layer encapsulation header to get the response from the
relevant node. For example, a classifier initiating OAM can generate
an ICMP echo request message, set the TTL field in the NSH header
[RFC8300] to 63 to get the response from the last SFF, and thereby
test the SFC availability. Alternatively, the initiator can set the
TTL to some other value to get the response from a specific SF and
thereby partially test SFC availability, or the initiator could send
OAM packets with sequentially incrementing TTL in the NSH to trace
the SFP.
It could be observed that ICMP as currently defined may not be able
to perform all required SFC OAM functions, but as explained above, it
can be used for some of the connectivity functions.
7.2. BFD / Seamless BFD
[RFC5880] defines the Bidirectional Forwarding Detection (BFD)
mechanism for failure detection. [RFC5881] and [RFC5884] define the
applicability of BFD in IPv4, IPv6, and MPLS networks. [RFC7880]
defines Seamless BFD (S-BFD), a simplified mechanism of using BFD.
[RFC7881] explains its applicability in IPv4, IPv6, and MPLS
networks.
BFD or S-BFD could be leveraged to perform the continuity function
for SF or SFC. An initiator could generate a BFD control packet and
set the "Your Discriminator" value in the control packet to identify
the last SFF. Upon receiving the control packet, the last SFF in the
SFC will reply back with the relevant DIAG code. The TTL field in
the NSH header could be used to perform a partial SFC availability
check. For example, the initiator can set the "Your Discriminator"
value to identify the SF that is intended to be tested and set the
TTL field in the NSH header in a way that it expires at the relevant
SF. How the initiator gets the Discriminator value to identify the
SF is outside the scope of this document.
7.3. In Situ OAM
[IOAM-NSH] defines how In situ OAM data fields [IPPM-IOAM-DATA] are
transported using the NSH header. [PROOF-OF-TRANSIT] defines a
mechanism to perform proof of transit to securely verify if a packet
traversed the relevant SFP or SFC. While the mechanism is defined
inband (i.e., it will be included in data packets), IOAM Option-
Types, such as IOAM Trace Option-Types, can also be used to perform
other SFC OAM functions, such as SFC tracing.
In situ OAM could be leveraged to perform SF availability and SFC
availability or performance measurement. For example, if SFC is
realized using NSH, the O bit in the NSH header could be set to
indicate the OAM traffic, as defined in Section 4.2 of [IOAM-NSH].
7.4. SFC Traceroute
[SFC-TRACE] defines a protocol that checks for path liveliness and
traces the service hops in any SFP. Section 3 of [SFC-TRACE] defines
the SFC trace packet format, while Sections 4 and 5 of [SFC-TRACE]
define the behavior of SF and SFF respectively. While [SFC-TRACE]
has expired, the proposal is implemented in Open Daylight and is
available.
An initiator can control the Service Index Limit (SIL) in an SFC
trace packet to perform SF and SFC availability tests.
8. Manageability Considerations
This document does not define any new manageability tools but
consolidates the manageability tool gap analysis for SF and SFC.
Table 2 below is not exhaustive.
+===========+===============+===============+========+==============+
|Layer | Configuration | Orchestration |Topology|Notification |
+===========+===============+===============+========+==============+
|Underlay | CLI, NETCONF | CLI, NETCONF |SNMP |SNMP, Syslog, |
|network | | | |NETCONF |
+-----------+---------------+---------------+--------+--------------+
|Overlay | CLI, NETCONF | CLI, NETCONF |SNMP |SNMP, Syslog, |
|network | | | |NETCONF |
+-----------+---------------+---------------+--------+--------------+
|Classifier | CLI, NETCONF | CLI, NETCONF |None |None |
+-----------+---------------+---------------+--------+--------------+
|SF | CLI, NETCONF | CLI, NETCONF |None |None |
+-----------+---------------+---------------+--------+--------------+
|SFC | CLI, NETCONF | CLI, NETCONF |None |None |
+-----------+---------------+---------------+--------+--------------+
Table 2: OAM Tool Gap Analysis
Configuration, orchestration, and other manageability tasks of SF and
SFC could be performed using CLI, NETCONF [RFC6241], etc.
While the NETCONF capabilities are readily available, as depicted in
Table 2, the information and data models are needed for
configuration, manageability, and orchestration for SFC. With
virtualized SF and SFC, manageability needs to be done
programmatically.
9. Security Considerations
Any security considerations defined in [RFC7665] and [RFC8300] are
applicable for this document.
The OAM information from the service layer at different components
may collectively or independently reveal sensitive information. The
information may reveal the type of service functions hosted in the
network, the classification rules and the associated service chains,
specific service function paths, etc. The sensitivity of the
information from the SFC layer raises a need for careful security
considerations.
The mapping and the rules information at the classifier component may
reveal the traffic rules and the traffic mapped to the SFC. The SFC
information collected at an SFC component may reveal the SFs
associated within each chain, and this information together with
classifier rules may be used to manipulate the header of synthetic
attack packets that may be used to bypass the SFC and trigger any
internal attacks.
The SF information at the SF component may be used by a malicious
user to trigger a Denial of Service (DoS) attack by overloading any
specific SF using rogue OAM traffic.
To address the above concerns, SFC and SF OAM should provide
mechanisms for mitigating:
* misuse of the OAM channel for denial of services,
* leakage of OAM packets across SFC instances, and
* leakage of SFC information beyond the SFC domain.
The documents proposing the OAM solution for SF components should
provide rate-limiting the OAM probes at a frequency guided by the
implementation choice. Rate-limiting may be applied at the
classifier, SFF, or the SF. The OAM initiator may not receive a
response for the probes that are rate-limited resulting in false
negatives, and the implementation should be aware of this. To
mitigate any attacks that leverage OAM packets, future documents
proposing OAM solutions should describe the use of any technique to
detect and mitigate anomalies and various security attacks.
The documents proposing the OAM solution for any service-layer
components should consider some form of message filtering to control
the OAM packets entering the administrative domain or prevent leaking
any internal service-layer information outside the administrative
domain.
10. IANA Considerations
This document has no IANA actions.
11. Informative References
[DOT1Q] IEEE, "IEEE Standard for Local and metropolitan area
networks--Bridges and Bridged Networks", IEEE 802.1Q-2014,
DOI 10.1109/IEEESTD.2014.6991462, November 2014,
<https://doi.org/10.1109/IEEESTD.2014.6991462>.
[EFM] IEEE, "IEEE Standard for Ethernet", IEEE 802.3-2018,
DOI 10.1109/IEEESTD.2018.8457469, June 2018,
<https://doi.org/10.1109/IEEESTD.2018.8457469>.
[IOAM-NSH] Brockners, F. and S. Bhandari, "Network Service Header
(NSH) Encapsulation for In-situ OAM (IOAM) Data", Work in
Progress, Internet-Draft, draft-ietf-sfc-ioam-nsh-04, 16
June 2020,
<https://tools.ietf.org/html/draft-ietf-sfc-ioam-nsh-04>.
[IPPM-IOAM-DATA]
Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields
for In-situ OAM", Work in Progress, Internet-Draft, draft-
ietf-ippm-ioam-data-10, 13 July 2020,
<https://tools.ietf.org/html/draft-ietf-ippm-ioam-data-
10>.
[PROOF-OF-TRANSIT]
Brockners, F., Bhandari, S., Mizrahi, T., Dara, S., and S.
Youell, "Proof of Transit", Work in Progress, Internet-
Draft, draft-ietf-sfc-proof-of-transit-06, 16 June 2020,
<https://tools.ietf.org/html/draft-ietf-sfc-proof-of-
transit-06>.
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<https://www.rfc-editor.org/info/rfc792>.
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330,
DOI 10.17487/RFC2330, May 1998,
<https://www.rfc-editor.org/info/rfc2330>.
[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393,
DOI 10.17487/RFC3393, November 2002,
<https://www.rfc-editor.org/info/rfc3393>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, DOI 10.17487/RFC4656, September 2006,
<https://www.rfc-editor.org/info/rfc4656>.
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, DOI 10.17487/RFC5357, October 2008,
<https://www.rfc-editor.org/info/rfc5357>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
DOI 10.17487/RFC5881, June 2010,
<https://www.rfc-editor.org/info/rfc5881>.
[RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
"Bidirectional Forwarding Detection (BFD) for MPLS Label
Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884,
June 2010, <https://www.rfc-editor.org/info/rfc5884>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[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,
DOI 10.17487/RFC6291, June 2011,
<https://www.rfc-editor.org/info/rfc6291>.
[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374,
DOI 10.17487/RFC6374, September 2011,
<https://www.rfc-editor.org/info/rfc6374>.
[RFC7498] Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for
Service Function Chaining", RFC 7498,
DOI 10.17487/RFC7498, April 2015,
<https://www.rfc-editor.org/info/rfc7498>.
[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>.
[RFC7679] Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
Ed., "A One-Way Delay Metric for IP Performance Metrics
(IPPM)", STD 81, RFC 7679, DOI 10.17487/RFC7679, January
2016, <https://www.rfc-editor.org/info/rfc7679>.
[RFC7680] Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
Ed., "A One-Way Loss Metric for IP Performance Metrics
(IPPM)", STD 82, RFC 7680, DOI 10.17487/RFC7680, January
2016, <https://www.rfc-editor.org/info/rfc7680>.
[RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
Pallagatti, "Seamless Bidirectional Forwarding Detection
(S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
<https://www.rfc-editor.org/info/rfc7880>.
[RFC7881] Pignataro, C., Ward, D., and N. Akiya, "Seamless
Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6,
and MPLS", RFC 7881, DOI 10.17487/RFC7881, July 2016,
<https://www.rfc-editor.org/info/rfc7881>.
[RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
Switched (MPLS) Data-Plane Failures", RFC 8029,
DOI 10.17487/RFC8029, March 2017,
<https://www.rfc-editor.org/info/rfc8029>.
[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>.
[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>.
[SFC-TRACE]
Penno, R., Quinn, P., Pignataro, C., and D. Zhou,
"Services Function Chaining Traceroute", Work in Progress,
Internet-Draft, draft-penno-sfc-trace-03, 30 September
2015,
<https://tools.ietf.org/html/draft-penno-sfc-trace-03>.
[Y.1731] ITU-T, "G.8013: Operations, administration and maintenance
(OAM) functions and mechanisms for Ethernet-based
networks", August 2015,
<https://www.itu.int/rec/T-REC-G.8013-201508-I/en>.
Acknowledgements
We would like to thank Mohamed Boucadair, Adrian Farrel, Greg Mirsky,
Tal Mizrahi, Martin Vigoureux, Tirumaleswar Reddy, Carlos Bernados,
Martin Duke, Barry Leiba, Éric Vyncke, Roman Danyliw, Erik Kline,
Benjamin Kaduk, Robert Wilton, Frank Brockner, Alvaro Retana, Murray
Kucherawy, and Alissa Cooper for their review and comments.
Contributors
Nobo Akiya
Ericsson
Email: nobo.akiya.dev@gmail.com
Authors' Addresses
Sam K. Aldrin
Google
Email: aldrin.ietf@gmail.com
Carlos Pignataro (editor)
Cisco Systems, Inc.
Email: cpignata@cisco.com
Nagendra Kumar (editor)
Cisco Systems, Inc.
Email: naikumar@cisco.com
Ram Krishnan
VMware
Email: ramkri123@gmail.com
Anoop Ghanwani
Dell
Email: anoop@alumni.duke.edu