Hi Behcet,
thank you for your review and thoughtful suggestions. I've updated the draft accordingly. Please find diff and the new working version attached. Also, several notes below are inlined under the GIM>> tag.
Regards,
Greg
On Mon, May 15, 2023 at 8:41 AM Behcet Sarikaya via Datatracker <noreply@xxxxxxxx> wrote:
Reviewer: Behcet Sarikaya
Review result: Ready with Nits
I am the assigned Gen-ART reviewer for this draft. The General Area
Review Team (Gen-ART) reviews all IETF documents being processed
by the IESG for the IETF Chair. Please treat these comments just
like any other last call comments.
For more information, please see the FAQ at
<https://wiki.ietf.org/en/group/gen/GenArtFAQ>.
Document: draft-ietf-sfc-multi-layer-oam-??
Reviewer: Behcet Sarikaya
Review Date: 2023-05-15
IETF LC End Date: 2023-05-17
IESG Telechat date: Not scheduled for a telechat
Summary:
This document defines Service Function Chaining (SFC) Operation, Maintenance
and Management (OAM) protocol. It defines in Section 6 ICMP like Echo
Request/Reply for SFC to do Operation, Maintenance and Management mainly for
Fault Management as SFC messages which constitutes the bulk of SFC OAM
protocol. As shepherd write-up explains it grew out of 3 documents all lead by
Greg Mirsky when he was with ZTE. Major issues:
Minor issues:
Author list has 6 people as also indicated in shepherd write-up. The document
already contains two names in the contributor list. Strongly recommend having
one more in the contributor list.
GIM>> This document is the result of merging three documents (one SFC WG and two individual drafts). Six authors listed on the front page contributed to at least two documents. We've tried to manage the situation fairly and with reason. I hope that is understandable and can be accepted.
Nits/editorial comments: please add the and as shown below:
This mechanism enables on-demand Continuity Check and
Connectivity Verification among other operations over SFC in networks
and addresses functionalities discussed in Sections 4.1, 4.2, and 4.3 of
[RFC8924].
GIM>> I updated the text. Please let me know if it reflects your view correctly.
The draft name contains multi-layer which is not mentioned elsewhere in the
draft.
GIM>> The draft went through several revisions, and that is reflected in some disconnect between its identifier and scope. I hope that is acceptable.
draft-ietf-sfc-nsh-tlv -> RFC 9263
GIM>> Done, thank you.
draft-ietf-sfc-oam-packet normative reference is in RFC Editor Queue
GIM>> Thank you for pointing that out. Will update it accordingly after the publication.
Behcet
SFC WG G. Mirsky
Internet-Draft Ericsson
Intended status: Standards Track W. Meng
Expires: 16 November 2023 ZTE Corporation
T. Ao
China Mobile
B. Khasnabish
K. Leung
Individual contributor
G. Mishra
Verizon Inc.
15 May 2023
Active OAM for Service Function Chaining (SFC)
draft-ietf-sfc-multi-layer-oam-24
Abstract
A set of requirements for active Operation, Administration, and
Maintenance (OAM) of Service Function Chains (SFCs) in a network is
presented in this document. Based on these requirements, an
encapsulation of active OAM messages in SFC and a mechanism to detect
and localize defects are described.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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 16 November 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Conventions . . . . . . . . . . . . . . . . . 4
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2.2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Requirements for Active OAM in SFC . . . . . . . . . . . . . 5
4. Active OAM Identification in the NSH . . . . . . . . . . . . 7
5. Active SFC OAM Header . . . . . . . . . . . . . . . . . . . . 7
6. Echo Request/Echo Reply for SFC . . . . . . . . . . . . . . . 8
6.1. Return Codes . . . . . . . . . . . . . . . . . . . . . . 10
6.2. Authentication in Echo Request/Reply . . . . . . . . . . 11
6.3. SFC Echo Request Transmission . . . . . . . . . . . . . . 11
6.3.1. Source TLV . . . . . . . . . . . . . . . . . . . . . 12
6.4. SFC Echo Request Reception . . . . . . . . . . . . . . . 14
6.4.1. Errored TLVs TLV . . . . . . . . . . . . . . . . . . 15
6.5. SFC Echo Reply Transmission . . . . . . . . . . . . . . . 16
6.5.1. Reply Service Function Path TLV . . . . . . . . . . . 16
6.5.2. Theory of Operation . . . . . . . . . . . . . . . . . 17
6.5.3. SFC Echo Reply Reception . . . . . . . . . . . . . . 19
6.5.4. Tracing an SFP . . . . . . . . . . . . . . . . . . . 19
6.6. Verification of the SFP Consistency . . . . . . . . . . . 19
6.6.1. SFP Consistency Verification packet . . . . . . . . . 20
6.6.2. SFF Information Record TLV . . . . . . . . . . . . . 20
6.6.3. SF Information Sub-TLV . . . . . . . . . . . . . . . 21
6.6.4. SF Information Sub-TLV Construction . . . . . . . . . 22
7. Security Considerations . . . . . . . . . . . . . . . . . . . 24
8. Operational Considerations . . . . . . . . . . . . . . . . . 25
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
10.1. SFC Active OAM Protocol . . . . . . . . . . . . . . . . 26
10.2. SFC Active OAM . . . . . . . . . . . . . . . . . . . . . 26
10.2.1. SFC Active OAM Message Type . . . . . . . . . . . . 26
10.2.2. SFC Active OAM Header Flags . . . . . . . . . . . . 27
10.3. SFC Echo Request/Echo Reply Parameters . . . . . . . . . 27
10.3.1. SFC Echo Request Flags . . . . . . . . . . . . . . . 27
10.3.2. SFC Echo Request/Echo Reply Message Types . . . . . 28
10.3.3. SFC Echo Reply Modes . . . . . . . . . . . . . . . . 29
10.3.4. SFC Echo Return Codes . . . . . . . . . . . . . . . 30
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10.4. SFC Active OAM TLV Type . . . . . . . . . . . . . . . . 31
10.5. SF Identifier Types . . . . . . . . . . . . . . . . . . 32
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
11.1. Normative References . . . . . . . . . . . . . . . . . . 33
11.2. Informative References . . . . . . . . . . . . . . . . . 34
Contributors' Addresses . . . . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction
[RFC7665] defines data plane elements necessary to implement a
Service Function Chaining (SFC). These include:
1. Classifiers that perform the classification of incoming packets.
Such classification may result in associating a received packet
to a service function chain.
2. Service Function Forwarders (SFFs) that are responsible for
forwarding traffic to one or more connected Service Functions
(SFs) according to the information carried in the SFC
encapsulation and handling traffic coming back from the SFs and
forwarding it to the next SFF.
3. SFs that are responsible for executing specific service treatment
on received packets.
There are different views from different levels of the SFC. One is
the service function chain, an entirely abstract view, which defines
an ordered set of SFs that must be applied to packets selected based
on classification rules. But service function chain doesn't specify
the exact mapping between SFFs and SFs. Thus, another logical
construct used in SFC is a Service Function Path (SFP). According to
[RFC7665], SFP is the instantiation of the SFC in the network and
provides a level of indirection between the entirely abstract SFCs
and a fully specified ordered list of SFFs and SFs identities that
the packet will visit when it traverses the SFC. The latter entity
is referred to as Rendered Service Path (RSP). The main difference
between SFP and RSP is that the former is the logical construct,
while the latter is the realization of the SFP via the sequence of
specific SFC data plane elements.
This document defines how active Operation, Administration and
Maintenance (OAM), per [RFC7799] definition of active OAM, is
identified when Network Service Header (NSH) [RFC8300] is used as the
SFC encapsulation. Following the analysis of SFC OAM in [RFC8924],
this document applies and, when necessary, extends requirements
listed in Section 4 of [RFC8924] for the use of active OAM in an SFP
supporting fault management and performance monitoring. Active OAM
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tools, conformant to the requirements listed in Section 3, improve,
for example, troubleshooting efficiency and defect localization in
SFP because they specifically address the architectural principles of
NSH. For that purpose, SFC Echo Request and Echo Reply are specified
in Section 6. This mechanism enables on-demand Continuity Check and
Connectivity Verification, among other operations, over SFC in
networks and addresses functionalities discussed in Sections 4.1,
4.2, and 4.3 of [RFC8924]. SFC Echo Request and Echo Reply, defined
in this document, can be used with encapsulations other than NSH, for
example, using MPLS encapsulation, as described in [RFC8595]. The
applicability of the SFC Echo Request/Reply mechanism in SFC
encapsulations other than NSH is outside the scope of this document.
2. Terminology and Conventions
The terminology defined in [RFC7665] is used extensively throughout
this document, and the reader is expected to be familiar with it.
In this document, SFC OAM refers to an active OAM [RFC7799] in an SFC
architecture. In this document, "Echo Request/Reply" and "SFC Echo
Request/Reply" are used interchangeably.
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.2. Acronyms
E2E: End-to-End
FM: Fault Management
NSH: Network Service Header
OAM: Operations, Administration, and Maintenance
RSP: Rendered Service Path
SF: Service Function
SFC: Service Function Chain
SFF: Service Function Forwarder
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SFP: Service Function Path
MAC: Message Authentication Code
3. Requirements for Active OAM in SFC
As discussed in [RFC8924], SFC-specific means are needed to perform
the OAM task of fault management (FM) in an SFC architecture,
including failure detection, defect characterization, and
localization. This document defines the set of requirements for
active FM OAM mechanisms to be used in an SFC architecture.
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
|SFI11| |SFI12| |SFI21| |SFI22| |SFI31| |SFI32|
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
\ / \ / \ /
+----------+ +----+ +----+ +----+
|Classifier|---|SFF1|---------|SFF2|----------|SFF3|
+----------+ +----+ +----+ +----+
Figure 1: An Example of SFC Data Plane Architecture
The architecture example depicted in Figure 1 considers a service
function chain that includes three distinct service functions. In
this example, the SFP traverses SFF1, SFF2, and SFF3. Each SFF is
connected to two instances of the same service function. End-to-end
(E2E) SFC OAM has the Classifier as the ingress and SFF3 as its
egress. Segment SFC OAM is between two elements that are part of the
same SFP. Following are the requirements for an FM SFC OAM, whether
with the E2E or segment scope:
REQ#1: Packets of active SFC OAM SHOULD be fate sharing with the
monitored SFC data in the forward direction from ingress toward
egress endpoint(s) of the OAM test.
The fate sharing, in the SFC environment, is achieved when a test
packet traverses the same path and receives the same treatment in the
underlay network layer as an SFC-encapsulated packet (e.g., NSH).
REQ#2: SFC OAM MUST support monitoring of the continuity of the
SFP between any of its elements.
An SFC failure might be declared when several consecutive test
packets are not received within a pre-determined time. For example,
in the E2E FM SFC OAM case, the egress, SFF3, in the example in
Figure 1, could be the entity that detects the SFP's failure by
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monitoring a flow of periodic test packets. The ingress may be
capable of recovering from the failure, e.g., using redundant SFC
elements. Thus, it is beneficial for the egress to signal the new
defect state to the ingress, which in this example is the Classifier.
Hence the following requirement:
REQ#3: SFC OAM MUST support Remote Defect Indication notification
by the egress to the ingress.
REQ#4: SFC OAM MUST support connectivity verification of the SFP.
Definition of the misconnection defect, entry, and exit criteria
are outside the scope of this document.
Once the SFF1 detects the defect, the objective of the SFC OAM
changes from the detection of a defect to defect characterization and
localization.
REQ#5: SFC OAM MUST support fault localization of the Loss of
Continuity Check within an SFP.
REQ#6: SFC OAM MUST support an SFP tracing to discover the RSP.
In the example presented in Figure 1, two distinct instances of the
same service function share the same SFF. In this example, the SFP
can be realized over several RSPs that use different instances of SF
of the same type. For instance, RSP1(SFI11--SFI21--SFI31) and
RSP2(SFI12--SFI22--SFI32). Available RSPs can be discovered using
the trace function discussed in Section 4.3 [RFC8924] or the
procedure defined in Section 6.5.4.
REQ#7: SFC OAM MUST have the ability to discover and exercise all
available RSPs in the network.
The SFC OAM layer model described in [RFC8924] offers an approach for
defect localization within a service function chain. As the first
step, the SFP's continuity for SFFs that are part of the same SFP
could be verified. After the reachability of SFFs has already been
verified, SFFs that serve an SF may be used as a test packet source.
In such a case, SFF can act as a proxy for another element within the
service function chain.
REQ#8: SFC OAM MUST be able to trigger on-demand FM with responses
being directed towards the initiator of such a request.
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4. Active OAM Identification in the NSH
Active SFC OAM combines OAM commands and/or data included in a
message that immediately follows the NSH. To identify the active SFC
OAM message, the "Next Protocol" field MUST be set to Active SFC OAM
(TBA1) (Section 10.1). The O bit in the NSH MUST be set, according
to [I-D.ietf-sfc-oam-packet]. A case when the O bit is clear and the
"Next Protocol" field value is set to Active SFC OAM (TBA1) is
considered an erroneous combination. An implementation MUST report
it. The notification mechanism is outside the scope of this
specification. The packet SHOULD be dropped. An implementation MAY
have control to enable the processing of the OAM payload.
5. Active SFC OAM Header
As demonstrated in Section 4 [RFC8924] and Section 3 of this
document, SFC OAM is required to perform multiple tasks. Several
active OAM protocols could be used to address all the requirements.
When IP/UDP encapsulation of an SFC OAM control message is used,
protocols can be demultiplexed using the destination UDP port number.
But extra IP/UDP headers, especially in an IPv6 network, add
noticeable overhead. This document defines Active OAM Header
(Figure 2) to demultiplex active OAM protocols on an SFC.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| V | Msg Type | Flags | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SFC Active OAM Control Packet ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SFC Active OAM Header
V - two-bit-long field indicates the current version of the SFC
active OAM header. The current value is 0. The version number is
to be incremented whenever a change is made that affects the
ability of an implementation to parse or process the SFC Active
OAM header correctly. For example, if syntactic or semantic
changes are made to any of the fixed fields.
Msg Type - six bits long field identifies OAM protocol, e.g., Echo
Request/Reply.
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Flags - eight bits long field carries bit flags that define
optional capability and thus processing of the SFC active OAM
control packet, e.g., optional timestamping. No flags are defined
in this document, and therefore, the bit flags MUST be zeroed on
transmission and ignored on receipt.
Length - two octets long field that is the length of the SFC
active OAM control packet in octets.
6. Echo Request/Echo Reply for SFC
Echo Request/Reply is a well-known active OAM mechanism extensively
used to verify a path's continuity, detect inconsistencies between a
state in control and the data planes, and localize defects in the
data plane. ICMP ([RFC0792] for IPv4 and [RFC4443] for IPv6
networks) and [RFC8029] are examples of broadly used active OAM
protocols based on the Echo Request/Reply principle. The SFC Echo
Request/Reply defined in this document conforms to REQ#1 (Section 3)
by using the NSH encapsulation of the monitored service. Further,
the mechanism addresses requirements REQ#2 through REQ#7, listed in
Section 3. Specifically, it can be used to check the continuity of
an SFP, trace an SFP, or localize the failure within an SFP. Also,
note that REQ#8 can be addressed by an extension of the SFC Echo
Request/Reply described in this document adding proxy capability.
The SFC Echo Request/Reply control message format is presented in
Figure 3.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| V | Reserved | Echo Request Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type | Reply mode | Return Code |Return Subcode |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender's Handle |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: SFC Echo Request/Reply Format
The interpretation of the fields is as follows:
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Version (V) is a two-bit field that indicates the current version
of the SFC Echo Request/Reply. The current value is 0. The
version number is to be incremented whenever a change is made that
affects the ability of an implementation to parse or process the
control packet correctly. If a packet presumed to carry an SFC
Echo Request/Reply is received at an SFF, and the SFF does not
understand the Version field value, the packet MUST be discarded,
and the event SHOULD be logged.
Reserved - fourteen-bit field. It MUST be zeroed on transmission
and ignored on receipt.
The Echo Request Flags is a two-octet bit vector field. A flag
defined in the Flags field of the SFC Active OAM header in
Figure 2 has no implication for those defined in the Echo Request
Flags field of an Echo Request/Reply message.
The Message Type is a one-octet field that reflects the packet
type. Value 1 identifies Echo Request and 2 - Echo Reply.
The Reply Mode is a one-octet field. It defines the type of the
return path requested by the sender of the Echo Request.
Return Codes and Subcodes are one-octet fields each. These can be
used to inform the sender about the result of processing its
request. Return Code values are provided in Table 1. For all
Return Code values defined in this document, the value of the
Return Subcode field MUST be set to zero.
The Sender's Handle is a four-octet field. It MUST be filled in
by the sender of the Echo Request and returned unchanged by the
Echo Reply sender (if a reply is mandated). The sender of the
Echo Request SHOULD use a pseudo-random number generator [RFC4086]
to set the value of the Sender's Handle field.
The Sequence Number is a four-octet field, and it is assigned by
the sender and can be, for example, used to detect missed replies.
The initial Sequence Number MUST be pseudo-randomly generated
[RFC4086] and then SHOULD be monotonically increasing in the
course of the test session.
TLV is a variable-length construct. Multiple TLVs MAY be placed in
an SFC Echo Request/Reply packet. None, one or more sub-TLVs may be
enclosed in the value part of a TLV, subject to the semantics of the
(outer) TLV. Figure 4 presents the format of an SFC Echo Request/
Reply TLV, where fields are defined as follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: SFC Echo Request/Reply TLV Format
Type - a one-octet field that characterizes the interpretation of
the Value field. Type values are allocated according to
Section 10.4.
Reserved - a one-octet field. The field MUST be zeroed on
transmission and ignored on receipt.
Length - a two-octet field equal to the Value field's length in
octets as an unsigned integer.
Value - a variable-length field. The value of the Type field
determines its interpretation and encoding.
6.1. Return Codes
The value of the Return Code field MUST be set to zero by the sender
of an Echo Request. The receiver of said Echo Request can set it to
one of the values listed in Table 1 in the corresponding Echo Reply
that it generates (in cases when the reply is requested).
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+=======+=============================================+
| Value | Description |
+=======+=============================================+
| 0 | No Return Code |
+-------+---------------------------------------------+
| 1 | Malformed Echo Request received |
+-------+---------------------------------------------+
| 2 | One or more of the TLVs was not understood |
+-------+---------------------------------------------+
| 3 | Authentication failed |
+-------+---------------------------------------------+
| 4 | TTL Exceeded |
+-------+---------------------------------------------+
| 5 | End of the SFP |
+-------+---------------------------------------------+
| 6 | Reply Service Function Path TLV is missing |
+-------+---------------------------------------------+
| 7 | Reply SFP was not found |
+-------+---------------------------------------------+
| 8 | Unverifiable Reply Service Function Path |
+-------+---------------------------------------------+
Table 1: SFC Echo Return Codes
6.2. Authentication in Echo Request/Reply
Authentication can be used to protect the integrity of the
information in SFC Echo Request and/or Echo Reply. In the [RFC9145]
a variable-length Context Header has been defined to protect the
integrity of the NSH and the payload. The header can also be used
for the optional encryption of sensitive metadata. MAC#1 (Message
Authentication Code) Context Header is more suitable for the
integrity protection of active SFC OAM, particularly of the SFC Echo
Request and Echo Reply, defined in this document. On the other hand,
using MAC#2 Context Header allows the detection of mishandling of the
O-bit by a transient SFC element.
6.3. SFC Echo Request Transmission
SFC Echo Request control packet MUST use the appropriate underlay
network encapsulation of the monitored SFP. If the NSH is used, Echo
Request MUST set O bit, as defined in [I-D.ietf-sfc-oam-packet]. NSH
MUST be immediately followed by the SFC Active OAM Header defined in
Section 4. The Message Type field's value in the SFC Active OAM
Header MUST be set to SFC Echo Request/Echo Reply value (1) per
Section 10.2.1.
Value of the Reply Mode field MUST be set to one of the following:
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* Do Not Reply (1) if one-way monitoring is desired. If the Echo
Request is used to measure synthetic packet loss, the receiver may
report loss measurement results to a remote node. Ways of
learning the identity of that node are outside the scope of this
specification.
* Reply via an IPv4/IPv6 UDP Packet (2). This likely will be the
most often used value.
* Reply via Application-Level Control Channel (3). Useful if the
SFP has bi-directional paths.
* Reply via Specified Path (4). This value requests the use of the
particular return path specified in the included TLV to verify bi-
directional continuity and may also increase the robustness of the
monitoring by selecting a more stable path. Section 6.5.1
provides an example of communicating an explicit path for the Echo
Reply.
* Reply via an IPv4/IPv6 UDP Packet with the data integrity
protection ((5). This value requests the use of the MAC Context
Header [RFC9145].
* Reply via Application-Level Control Channel with the data
integrity protection (6). This value requests the use of the MAC
Context Header [RFC9145].
* Reply via Specified Path with the the data integrity protection
(7). This value requests the use of the MAC Context Header
[RFC9145].
6.3.1. Source TLV
The responder to the SFC Echo Request encapsulates the SFC Echo Reply
message in IP/UDP packet if the Reply mode is "Reply via an IPv4/IPv6
UDP Packet". Because the NSH does not identify the ingress node that
generated the Echo Request, the source ID MUST be included in the
message and used as the IP destination address and destination UDP
port number of the SFC Echo Reply. The sender of the SFC Echo
Request MUST include an SFC Source TLV (Figure 5).
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source ID | Reserved1 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Port Number | Reserved2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: SFC Source TLV
where
Source ID Type is a one-octet field and has the value of 1
Section 10.4.
Reserved1 - one-octet field. The field MUST be zeroed on
transmission and ignored on receipt.
Length is a two-octet field, and the value equals the length of
the data following the Length field counted in octets. The value
of the Length field can be 8 or 20. If the value of the field is
neither, the Source TLV is considered to be malformed.
Port Number is a two-octet field. It contains the UDP port number
of the sender of the SFC OAM control message. The value of the
field MUST be used as the destination UDP port number in the IP/
UDP encapsulation of the SFC Echo Reply message.
Reserved2 is a two-octet field. The field MUST be zeroed on
transmit and ignored on receipt.
IP Address field contains the IP address of the sender of the SFC
OAM control message, IPv4 or IPv6. The value of the field MUST be
used as the destination IP address in the IP/UDP encapsulation of
the SFC Echo Reply message.
A single Source ID TLV for each address family, i.e., IPv4 and IPv6,
MAY be present in an SFC Echo Request message. If the Source TLVs
for both address families are present in an SFC Echo Request message,
the SFF MUST NOT replicate an SFC Echo Reply but choose the
destination IP address for the one SFC Echo Reply it sends based on
the local policy. If more than one Source ID TLV per the address
family is present, the receiver MUST use the first TLV and ignore the
rest.
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6.4. SFC Echo Request Reception
Punting a received SFC Echo Request to the control plane is triggered
by one of the following packet processing exceptions: NSH TTL
expiration, NSH Service Index (SI) expiration, or the receiver is the
terminal SFF for an SFP.
An SFF that received the SFC Echo Request MUST validate the packet as
follows:
1. If the SFC Echo Request is integrity-protected, the receiving
SFF first MUST verify the authentication.
2. Validate the Source TLV, as defined in Section 6.3.1.
3. Suppose the authentication validation has failed and the Source
TLV is considered properly formatted. In that case, the SFF
MUST send to the system identified in the Source TLV (see
Section 6.5), according to a rate-limit control mechanism, an
SFC Echo Reply with the Return Code set to "Authentication
failed" and the Subcode set to zero.
4. If the Source TLV is determined malformed, the received SFC Echo
Request processing is stopped, the message is dropped, and the
event SHOULD be logged, according to a rate-limiting control for
logging.
5. If the authentication is validated successfully, the SFF that
has received an SFC Echo Request verifies the rest of the
packet's general sanity.
6. If the packet is not well-formed, the receiver SFF SHOULD send
an SFC Echo Reply with the Return Code set to "Malformed Echo
Request received" and the Subcode set to zero under the control
of the rate-limiting mechanism to the system identified in the
Source TLV (see Section 6.5).
7. If there are any TLVs that the SFF does not understand, the SFF
MUST send an SFC Echo Reply with the Return Code set to 2 ("One
or more TLVs was not understood") and set the Subcode to zero.
Also, the SFF MAY include an Errored TLVs TLV (Section 6.4.1)
that, as sub-TLVs, contains only the misunderstood TLVs.
8. Sender's Handle and Sequence Number fields are not examined but
are copied in the SFC Echo Reply message.
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9. If the sanity check of the received Echo Request succeeded, then
the SFF at the end of the SFP MUST set the Return Code value to
5 ("End of the SFP") and the Subcode set to zero.
10. If the SFF is not at the end of the SFP and the TTL value is 1,
the value of the Return Code MUST be set to 4 ("TTL Exceeded")
and the Subcode set to zero.
11. In all other cases, SFF MUST set the Return Code value to 0 ("No
Return Code") and the Subcode set to zero.
6.4.1. Errored TLVs TLV
If the Return Code for the Echo Reply is determined as 2 ("One or
more TLVs was not understood"), the Errored TLVs TLV might be
included in an Echo Reply. The use of this TLV is meant to inform
the sender of an Echo Request of TLVs either not supported by an
implementation or parsed and found to be in error.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Errored TLVs | Reserved | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
. .
. .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Errored TLVs TLV
where
The Errored TLVs Type MUST be set to 2 (Section 10.4).
Reserved - one-octet field. The field MUST be zeroed on
transmission and ignored on receipt.
Length - two-octet field equal to the length of the Value field in
octets.
The Value field contains the TLVs, encoded as sub-TLVs (as shown
in Figure 7), that were not understood or failed to be parsed
correctly.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLV Type | Reserved | Sub-TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Sub-TLV Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Not Understood or Failed TLV as Sub-TLV
where
The Sub-TLV's Type - a copy of the first octet of the not
understood or failed to be parsed TLV.
Reserved - one-octet field. The field MUST be zeroed on
transmission and ignored on receipt.
Sub-TLV Length - two-octet field equal to the value of the Length
field of the errored TLV.
The Sub-TLV Value field contains data that follow the Length field
in the errored TLV.
6.5. SFC Echo Reply Transmission
The "Reply Mode" field directs whether and how the Echo Reply message
should be sent. The Echo Request sender MAY use TLVs to request that
the corresponding Echo Reply be transmitted over the specified path.
Section 6.5.1 provides an example of a TLV that specifies the return
path of the Echo Reply. Value 1 is the "Do not reply" mode and
suppresses the Echo Reply packet transmission. The default value (2)
for the Reply mode field requests sending the Echo Reply packet out-
of-band as an IPv4 or IPv6 UDP packet.
6.5.1. Reply Service Function Path TLV
While SFC Echo Request always traverses the SFP it is directed to by
using NSH, the corresponding Echo Reply usually is sent without NSH.
In some cases, an operator might choose to direct the responder to
send the Echo Reply with NSH over a particular SFP. This section
defines a new Type-Length-Value (TLV), Reply Service Function Path
TLV, for Reply via Specified Path mode of SFC Echo Reply.
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The Reply Service Function Path TLV can provide an efficient
mechanism to test SFCs, such as bidirectional and hybrid SFC, as
defined in Section 2.2 [RFC7665]. For example, it allows an operator
to test both directions of the bidirectional or hybrid SFP with a
single SFC Echo Request/Echo Reply operation.
The Reply Service Function Path TLV carries the information that
sufficiently identifies the return SFP that the SFC Echo Reply
message is expected to follow. The format of Reply Service Function
Path TLV is shown in Figure 8.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reply SFP | Reserved | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reply Service Function Path Identifier | Service Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: SFC Reply TLV Format
where:
* Reply SFP (Service Function Path) Type (3): this is is a one-octet
field and indicates the TLV that contains information about the
SFC Reply path.
* Reserved: is a one-octet field. The field MUST be zeroed on
transmission and ignored on receipt.
* Length: is a two-octet field, MUST be equal to 4
* Reply Service Function Path Identifier: SFP identifier for the
path that the SFC Echo Reply message is requested to be sent over.
* Service Index: the value for the Service Index field in the NSH of
the SFC Echo Reply message.
6.5.2. Theory of Operation
[RFC7110] defined mechanism to control return path for MPLS LSP Echo
Reply. In SFC's case, the return path is an SFP along which the SFC
Echo Reply message MUST be transmitted. Hence, the Reply Service
Function Path TLV included in the SFC Echo Request message MUST
sufficiently identify the SFP that the sender of the Echo Request
message expects the receiver to use for the corresponding SFC Echo
Reply.
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When sending an Echo Request, the sender MUST set the value of Reply
Mode field to "Reply via Specified Path", defined in Section 6.3, and
if the specified path is an SFC path, the Request MUST include Reply
Service Function Path TLV. The Reply Service Function Path TLV
consists of the identifier of the reverse SFP and an appropriate
Service Index.
If the NSH of the received SFC Echo Request includes the MAC Context
Header, the packet's authentication MUST be verified before using any
data. If the verification fails, the receiver MUST stop processing
the SFC Return Path TLV and MUST send the SFC Echo Reply with the
Return Codes value set to the value Authentication failed from the
IANA's Return Codes sub-registry of the SFC Echo Request/Echo Reply
Parameters registry.
The destination SFF of the SFP being tested or the SFF at which SFC
TTL expired (as per [RFC8300]) may be sending the Echo Reply is
referred to as responding SFF. The processing described below
equally applies to both cases.
If the Echo Request message with Reply Service Function Path TLV,
received by the responding SFF, has Reply Mode value of "Reply via
Specified Path" but no Reply Service Function Path TLV is present,
then the responding SFF MUST send Echo Reply with Return Code set to
6 ("Reply Service Function Path TLV is missing"). If the responding
SFF cannot find the requested SFP it MUST send Echo Reply with Return
Code set to 7 ("Reply SFP was not found") and include the Reply
Service Function Path TLV from the Echo Request message.
Suppose the SFC Echo Request receiver cannot determine whether the
specified return path SFP has the route to the initiator. In that
case, it SHOULD set the value of the Return Codes field to 8
("Unverifiable Reply Service Function Path"). The receiver MAY drop
the Echo Request when it cannot determine whether SFP's return path
has the route to the initiator. When sending Echo Request, the
sender SHOULD choose a proper source address according to the
specified return path SFP to help the receiver find the viable return
path.
6.5.2.1. Bi-directional SFC Case
The ability to specify the return path for an Echo Reply might be
used in the case of bi-directional SFC. The egress SFF of the
forward SFP might not be co-located with a classifier of the reverse
SFP, and thus the egress SFF has no information about the reverse
path of an SFC. Because of that, even for bi-directional SFC, a
reverse SFP needs to be indicated in a Reply Service Function Path
TLV in the Echo Request message.
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6.5.3. SFC Echo Reply Reception
An SFF SHOULD NOT accept SFC Echo Reply unless the received message
passes the following checks:
* the received SFC Echo Reply is well-formed;
* the matching SFC Echo Request is found, that is, the value of the
Sender's Handle in the Echo Request sent is equal to the value of
Sender's Handle in the Echo Reply received;
* all other checks passed and the Sequence Number in the Echo
Request sent matches to the Sequence Number in the Echo Reply
received.
6.5.4. Tracing an SFP
SFC Echo Request/Reply can be used to isolate a defect detected in
the SFP and trace an RSP. As with ICMP echo request/reply [RFC0792]
and MPLS echo request/reply [RFC8029], this mode is referred to as
"traceroute". In the traceroute mode, the sender transmits a
sequence of SFC Echo Request messages starting with the NSH TTL value
set to 1 and is incremented by 1 in each next Echo Request packet.
The sender stops transmitting SFC Echo Request packets when the
Return Code in the received Echo Reply equals 5 ("End of the SFP").
Suppose a specialized information element (e.g., IPv6 Flow Label
[RFC6437] or Flow ID [RFC9263]) is used for distributing the load
across Equal Cost Multi-Path or Link Aggregation Group paths. In
that case, such an element SHOULD also be used for the SFC OAM
traffic. Doing so is meant to induce the SFC Echo Request to follow
the same RSP as the monitored flow.
6.6. Verification of the SFP Consistency
The consistency of an SFP can be verified by comparing the view of
the SFP from the control or management plane with information
collected from traversing by an SFC NSH Echo Request message. Every
SFF that receives a Consistency Verification Request (CVReq)
(specified in Section 6.6.1) MUST perform the following actions:
* Collect information about the SFs traversed by the CVReq packet
and send it to the ingress SFF as CVRep packet over IP network;
* Forward the CVReq to the next downstream SFF if the one exists.
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As a result, the ingress SFF collects information about all traversed
SFFs and SFs, information on the actual path the CVReq packet has
traveled. That information can be used to verify the SFC's path
consistency. The mechanism for the SFP consistency verification is
outside the scope of this document.
6.6.1. SFP Consistency Verification packet
For the verification of an SFP consistency, two types of SFC Active
OAM messages are defined in addition to the SFC Echo Request/Reply
messages. Their SFC Echo Request/Echo Response Message Types are as
follows:
* 3 - SFP Consistency Verification Request
* 4 - SFP Consistency Verification Reply
Upon receiving the CVReq, the SFF MUST respond with the Consistency
Verification Reply (CVRep). The SFF MUST include the SFs
information, as described in Section 6.6.3 and Section 6.6.2.
6.6.2. SFF Information Record TLV
For the received CVReq, an SFF is expected to include in the CVRep
message the information about SFs that are available from that SFF
instance for the specified SFP. The SFF MUST include SFF Information
Record TLV (Figure 9) in CVRep message. Every SFF sends back a
single CVRep message, including information on all the SFs attached
to that SFF on the SFP, as requested in the received CVReq message
using the SF Information sub-TLV (Section 6.6.3).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|SFF Record TLV | Reserved | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Path Identifier (SPI) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SF Information Sub-TLV |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 9: SFF Information Record TLV
The SFF Information Record TLV is a variable-length TLV that includes
the information of all SFs available from the particular SFF instance
for the specified SFP. Figure 9 presents the format of an SFF
Information Record TLV, where fields are defined as the following:
SFF Record TLV - one-octet field. The value is (4)
(Section 10.4).
Reserved - one-octet field. The field MUST be zeroed on
transmission and ignored on receipt.
Service Path Identifier (SPI): The identifier of SFP to which all
the SFs in this TLV belong.
SF Information Sub-TLV: The sub-TLV is as defined in Figure 10.
If the NSH of the received SFC Echo Reply includes the MAC Context
Header [RFC9145], the authentication of the packet MUST be verified
before using any data. If the verification fails, the receiver MUST
stop processing the SFF Information Record TLV and notify an
operator. The notification mechanism SHOULD include control of rate-
limited messages. Specification of the notification mechanism is
outside the scope of this document.
6.6.3. SF Information Sub-TLV
Every SFF receiving a CVReq packet MUST include the SF characteristic
data into the CVRep packet. The format of an SF Information sub-TLV,
included in a CVRep packet, is shown in Figure 10.
After the CVReq message traverses the SFP, all the information about
the SFs on the SFP is available from the TLVs included in CVRep
messages.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SF sub-TLV | Reserved | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Service Index | SF Type | SF ID Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SF Identifier |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 10: Service Function Information Sub-TLV
SF sub-TLV Type: one-octet long field. The value is (5)
(Section 10.4).
Reserved - one-octet field. The field MUST be zeroed on
transmission and ignored on receipt.
Length - two-octet long field. The value of this field is the
length of the data following the Length field counted in octets.
Service Index - indicates the SF's position on the SFP.
SF Type - two-octet field. It is defined in [RFC9015] and
indicates the type of SF, e.g., Firewall, Deep Packet Inspection,
WAN optimization controller, etc.
SF ID Type - one-octet field with values defined as Section 10.5.
SF Identifier - an identifier of the SF. The length of the SF
Identifier depends on the type of the SF ID Type. For example, if
the SF Identifier is its IPv4 address, the SF Identifier should be
32 bits.
6.6.4. SF Information Sub-TLV Construction
Each SFF in the SFP MUST send one and only one CVRep corresponding to
the CVReq. If only one SF is attached to the SFF in such SFP, only
one SF information sub-TLV is included in the CVRep. If several SFs
attached to the SFF in the SFP, SF Information sub-TLV MUST be
constructed as described below in either Section 6.6.4.1 and
Section 6.6.4.2.
6.6.4.1. Multiple SFs as Hops of an SFP
Multiple SFs attached to the same SFF can be the hops of the SFP.
The service indexes of these SFs on that SFP will be different.
Service function types of these SFs could be different or be the
same. Information about all SFs MAY be included in the CVRep
message. Information about each SF MUST be listed as separate SF
Information sub-TLVs in the CVRep message. The same SF can even
appear more than once in an SFP with a different service index.
An example of the SFP consistency verification procedure for this
case is shown in Figure 11. The Service Function Path (SPI=x) is
SF1->SF2->SF4->SF3. The SF1, SF2, and SF3 are attached to SFF1, and
SF4 is attached to SFF2. The CVReq message is sent to the SFFs in
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the sequence of the SFP(SFF1->SFF2->SFF1). Every SFF(SFF1, SFF2)
replies with the information of SFs belonging to the SFP. The SF
information Sub-TLV in Figure 10 contains information for each SF
(SF1, SF2, SF3, and SF4).
SF1 SF2 SF4 SF3
+------+------+ | |
CVReq ......> SFF1 ......> SFF2 ......> SFF1
(SPI=x) . . .
<............ <.......... <...........
CVRep1(SF1,SF2) CVRep2(SF4) CVRep3(SF3)
Figure 11: Example 1 for CVRep with multiple SFs
6.6.4.2. Multiple SFs for load balance
Multiple SFs may be attached to the same SFF to spread the load; in
other words, that means that the particular traffic flow will
traverse only one of these SFs. These SFs have the same Service
Function Type and Service Index. For this case, the SF ID Type,
which must be the same for all of these SFs, appears once but all of
their SF Identifiers will appear concatenated in the SF Identifier
area of the Sub-TLV (see Figure 10). The number of these SFs can be
calculated from the SF ID Type and the value of the Length field of
the sub-TLV.
An example of the SFP consistency verification procedure for this
case is shown in Figure 12. The Service Function Path (SPI=x) is
SF1a/SF1b->SF2a/SF2b. The Service Functions SF1a and SF1b are
attached to SFF1, which balances the load among them. The Service
Functions SF2a and SF2b are attached to SFF2, which, in turn,
balances its load between them. The CVReq message is sent to the
SFFs in the sequence of the SFP (i.e. SFF1->SFF2). Every SFF (SFF1,
SFF2) replies with the information of SFs belonging to the SFP. The
SF information Sub-TLV in Figure 10 contains information for all SFs
at that hop.
/SF1a /SF2a
\SF1b \SF2b
| |
SFF1 SFF2
CVReq .........> . .........> .
(SPI=x) . .
<............ <...............
CVRep1({SF1a,SF1b}) CVRep2({SF2a,SF2b})
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Figure 12: Example 2 for CVRep with multiple SFs
7. Security Considerations
When the integrity protection for SFC active OAM, and SFC Echo
Request/Reply in particular, is required, using one of the Context
Headers defined in [RFC9145] is RECOMMENDED. MAC#1 Context Header
could be more suitable for active SFC OAM because it does not require
re-calculation of the MAC when the value of the NSH Base Header's TTL
field is changed. Integrity protection for SFC active OAM can also
be achieved using mechanisms in the underlay data plane. For
example, if the underlay is an IPv6 network, IP Authentication Header
[RFC4302] or IP Encapsulating Security Payload Header [RFC4303] can
be used to provide integrity protection. Confidentiality for the SFC
Echo Request/Reply exchanges can be achieved using the IP
Encapsulating Security Payload Header [RFC4303]. Also, the security
needs for SFC Echo Request/Reply are similar to those of ICMP ping
[RFC0792], [RFC4443] and MPLS LSP ping [RFC8029].
There are at least three approaches to attacking a node in the
overlay network using the mechanisms defined in the document. One is
a Denial-of-Service attack, sending SFC Echo Requests to overload an
element of the SFC. The second may use spoofing, hijacking,
replying, or otherwise tampering with SFC Echo Requests and/or
replies to misrepresent, alter the operator's view of the state of
the SFC. The third is an unauthorized source using an SFC Echo
Request/Reply to obtain information about the SFC and/or its
elements, e.g., SFFs and/or SFs.
It is RECOMMENDED that implementations throttle the number of SFC
Echo Request/Echo Reply messages going to the control plane to
mitigate potential Denial-of-Service attacks.
Reply and spoofing attacks involving faking or replying to SFC Echo
Reply messages would have to match the Sender's Handle and Sequence
Number of an outstanding SFC Echo Request message, which is highly
unlikely for off-path attackers. A non-matching reply would be
discarded.
To protect against unauthorized sources trying to obtain information
about the overlay and/or underlay, an implementation MAY check that
the source of the Echo Request is indeed part of the SFP.
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Also, since the Service Function Information sub-TLV discloses
information about the SFP, the spoofed CVReq packet may be used to
obtain network information. Thus it is RECOMMENDED that
implementations provide a means of checking the source addresses of
CVReq messages, specified in SFC Source TLV Section 6.3.1, against an
access list before accepting the message.
8. Operational Considerations
This section provides information about operational aspects of the
SFC NSH Echo Request/Reply according to recommendations in [RFC5706].
SFC NSH Echo Request/Reply provides essential OAM functions for
network operators. SFC NSH Echo Request/Reply is intended to detect
and localize defects in an SFC. For example, by comparing results of
the trace function in operational and failed states, an operator can
locate the defect, e.g., the connection between SFF1 and SFF2
(Figure 1). After narrowing down a failure to an overlay link, a
more specific failure location can be determined using OAM tools in
the underlay network. The mechanism defined in this document can be
used on-demand or for periodic validation of an SFP or RSP. Because
the protocol makes use of the control plane which may have limited
capacity, an operator must be able to rate limit Echo Request and
Echo Reply messages. A reasonably selected default interval between
Echo Request control packets can provide additional benefit for an
operator. If the protocol is incrementally deployed in the NSH
domain, SFC elements, e.g., Classifier or SFF, that don't support
Active SFC OAM will discard protocol's packets. SFC NSH Echo
Request/Reply also can be used in combination with the existing
mechanisms discussed in [RFC8924], filling the gaps and extending
their functionalities.
Management of the SFC NSH Echo Request/Reply protocol can be provided
by a proprietary tool, e.g., command line interface, or based on a
data model, structured or standardized.
9. Acknowledgments
The authors greatly appreciate the thorough review and the most
helpful comments from Dan Wing, Dirk von Hugo, Mohamed Boucadair,
Donald Eastlake, Carlos Pignataro, and Frank Brockners. The authors
are thankful to John Drake for his review and the reference to the
work on BGP Control Plane for NSH SFC. The authors express their
appreciation to Joel M. Halpern for his suggestion about the load-
balancing scenario.
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10. IANA Considerations
The terms used in the IANA Considerations below are intended to be
consistent with [RFC8126].
10.1. SFC Active OAM Protocol
IANA is requested to assign a new type from the sub-registry NSH Next
Protocol of the Network Service Header (NSH) Parameters registry as
follows:
+=======+================+===============+
| Value | Description | Reference |
+=======+================+===============+
| TBA1 | SFC Active OAM | This document |
+-------+----------------+---------------+
Table 2: SFC Active OAM Protocol
10.2. SFC Active OAM
IANA is requested to create an SFC Active OAM registry containing the
sub-registries listed below.
10.2.1. SFC Active OAM Message Type
IANA is requested to create in the SFC Active OAM registry a sub-
registry as follows:
Sub-registry Name: SFC Active OAM Message Type.
Assignment Policy:
2-31 IETF Review
32-62 First Come First Served
Reference: [this document]
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+========+=============================+===============+
| Value | Description | Reference |
+========+=============================+===============+
| 0 | Reserved | This document |
+--------+-----------------------------+---------------+
| 1 | SFC Echo Request/Echo Reply | This document |
+--------+-----------------------------+---------------+
| 2 - 31 | Unassigned | This document |
+--------+-----------------------------+---------------+
| 32-62 | Unassigned | This document |
+--------+-----------------------------+---------------+
| 63 | Reserved | This document |
+--------+-----------------------------+---------------+
Table 3: SFC Active OAM Message Type
10.2.2. SFC Active OAM Header Flags
IANA is requested to create in the SFC Active OAM Registry the sub-
registry SFC Active OAM Flags.
This sub-registry tracks the assignment of 8 flags in the Flags field
of the SFC Active OAM Header. The flags are numbered from 0 (most
significant bit, transmitted first) to 7.
New entries are assigned by Standards Action.
+============+=============+===============+
| Bit Number | Description | Reference |
+============+=============+===============+
| 7-0 | Unassigned | This document |
+------------+-------------+---------------+
Table 4: SFC Active OAM Header Flags
10.3. SFC Echo Request/Echo Reply Parameters
IANA is requested to create in the SFC Active OAM Registry the sub-
registry SFC Echo Request/Echo Reply Parameters.
10.3.1. SFC Echo Request Flags
IANA is requested to create in the SFC Echo Request/Echo Reply
Parameters the SFC Echo Request Flags sub-registry.
This sub-registry tracks the assignment of 16 flags in the SFC Echo
Request Flags field of the SFC Echo Request message. The flags are
numbered from 0 (most significant bit, transmitted first) to 15.
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New entries are assigned by Standards Action.
+============+=============+===============+
| Bit Number | Description | Reference |
+============+=============+===============+
| 15-0 | Unassigned | This document |
+------------+-------------+---------------+
Table 5: SFC Echo Request Flags
10.3.2. SFC Echo Request/Echo Reply Message Types
IANA is requested to create in the SFC Echo Request/Echo Reply
Parameters the SFC Echo Request/Echo Reply Message Types sub-registry
as follows:
Sub-registry Name: SFC Echo Request/Echo Reply Message Types
Assignment Policy:
5 - 175 IETF Review
176 - 239 First Come First Served
Reference: [this document]
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+===========+======================================+===============+
| Value | Description | Reference |
+===========+======================================+===============+
| 0 | Reserved | This document |
+-----------+--------------------------------------+---------------+
| 1 | SFC Echo Request | This document |
+-----------+--------------------------------------+---------------+
| 2 | SFC Echo Reply | This document |
+-----------+--------------------------------------+---------------+
| 3 | SFP Consistency Verification Request | This document |
+-----------+--------------------------------------+---------------+
| 4 | SFP Consistency Verification Reply | This document |
+-----------+--------------------------------------+---------------+
| 5 - 175 | Unassigned | This document |
+-----------+--------------------------------------+---------------+
| 176 - 239 | Unassigned | This document |
+-----------+--------------------------------------+---------------+
| 240 - 251 | Experimental | This document |
+-----------+--------------------------------------+---------------+
| 252 - 254 | Private Use | This document |
+-----------+--------------------------------------+---------------+
| 255 | Reserved | This document |
+-----------+--------------------------------------+---------------+
Table 6: SFC Echo Request/Echo Reply Message Types
10.3.3. SFC Echo Reply Modes
IANA is requested to create in the SFC Echo Request/Echo Reply
Parameters registry the new sub-registry as follows:
Sub-registry Name: SFC Echo Reply Mode
Assignment Policy:
8 - 175 IETF Review
176 - 239 First Come First Served
Reference: [this document]
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+=======+====================================+===============+
| Value | Description | Reference |
+=======+====================================+===============+
| 0 | Reserved | This document |
+-------+------------------------------------+---------------+
| 1 | Do Not Reply | This document |
+-------+------------------------------------+---------------+
| 2 | Reply via an IPv4/IPv6 UDP Packet | This document |
+-------+------------------------------------+---------------+
| 3 | Reply via Application-Level | This document |
| | Control Channel | |
+-------+------------------------------------+---------------+
| 4 | Reply via Specified Path | This document |
+-------+------------------------------------+---------------+
| 5 | Reply via an IPv4/IPv6 UDP Packet | This document |
| | with the data integrity protection | |
+-------+------------------------------------+---------------+
| 6 | Reply via Application-Level | This document |
| | Control Channel with the data | |
| | integrity protection | |
+-------+------------------------------------+---------------+
| 7 | Reply via Specified Path with the | This document |
| | data integrity protection | |
+-------+------------------------------------+---------------+
| 8 - | Unassigned | This document |
| 175 | | |
+-------+------------------------------------+---------------+
| 176 - | Unassigned | This document |
| 239 | | |
+-------+------------------------------------+---------------+
| 240 - | Experiemntal | This document |
| 251 | | |
+-------+------------------------------------+---------------+
| 252 - | Private Use | This document |
| 254 | | |
+-------+------------------------------------+---------------+
| 255 | Reserved | This document |
+-------+------------------------------------+---------------+
Table 7: SFC Echo Reply Modes
10.3.4. SFC Echo Return Codes
IANA is requested to create in the SFC Echo Request/Echo Reply
Parameters registry the new sub-registry as follows:
Sub-registry Name: SFC Echo Return Codes
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Assignment Policy:
9 - 191 IETF Review
192 - 251 First Come First Served
Reference: [this document]
+=========+=================================+===============+
| Value | Description | Reference |
+=========+=================================+===============+
| 0 | No Return Code | This document |
+---------+---------------------------------+---------------+
| 1 | Malformed Echo Request received | This document |
+---------+---------------------------------+---------------+
| 2 | One or more of the TLVs was not | This document |
| | understood | |
+---------+---------------------------------+---------------+
| 3 | Authentication failed | This document |
+---------+---------------------------------+---------------+
| 4 | TTL Exceeded | This document |
+---------+---------------------------------+---------------+
| 5 | End of the SFP | This document |
+---------+---------------------------------+---------------+
| 6 | Reply Service Function Path TLV | This document |
| | is missing | |
+---------+---------------------------------+---------------+
| 7 | Reply SFP was not found | This document |
+---------+---------------------------------+---------------+
| 8 | Unverifiable Reply Service | This document |
| | Function Path | |
+---------+---------------------------------+---------------+
| 9 -191 | Unassigned | This document |
+---------+---------------------------------+---------------+
| 192-251 | Unassigned | This document |
+---------+---------------------------------+---------------+
| 252-254 | Private Use | This document |
+---------+---------------------------------+---------------+
| 255 | Reserved | This document |
+---------+---------------------------------+---------------+
Table 8: SFC Echo Return Codes
10.4. SFC Active OAM TLV Type
IANA is requested to create in the in the SFC Active OAM Registry the
sub-registry as follows:
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Registry Name: SFC Active OAM TLV Type
Assignment Policy:
6 -175 IETF Review
176 - 239 First Come First Served
Reference: [this document]
+===========+===================================+===============+
| Value | Description | Reference |
+===========+===================================+===============+
| 0 | Reserved | This document |
+-----------+-----------------------------------+---------------+
| 1 | Source ID TLV | This document |
+-----------+-----------------------------------+---------------+
| 2 | Errored TLVs | This document |
+-----------+-----------------------------------+---------------+
| 3 | Reply Service Function Path Type | This document |
+-----------+-----------------------------------+---------------+
| 4 | SFF Information Record Type | This document |
+-----------+-----------------------------------+---------------+
| 5 | SF Information | This document |
+-----------+-----------------------------------+---------------+
| 6 - 175 | Unassigned | This document |
+-----------+-----------------------------------+---------------+
| 176 - 239 | Unassigned | This document |
+-----------+-----------------------------------+---------------+
| 240 - 251 | Experimental | This document |
+-----------+-----------------------------------+---------------+
| 252 - 254 | Private Use | This document |
+-----------+-----------------------------------+---------------+
| 255 | Reserved | This document |
+-----------+-----------------------------------+---------------+
Table 9: SFC Active OAM TLV Type Registry
10.5. SF Identifier Types
IANA is requested to create in the SF Types registry [RFC9263] the
sub-registry as follows:
Registry Name: SF Identifier Types
Assignment Policy:
4 -191 IETF Review
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192 - 251 First Come First Served
Reference: [this document]
+=========+=============+===============+
| Value | Description | Reference |
+=========+=============+===============+
| 0 | Reserved | This document |
+---------+-------------+---------------+
| 1 | IPv4 | This document |
+---------+-------------+---------------+
| 2 | IPv6 | This document |
+---------+-------------+---------------+
| 3 | MAC | This document |
+---------+-------------+---------------+
| 4 -191 | Unassigned | This document |
+---------+-------------+---------------+
| 192-251 | Unassigned | This document |
+---------+-------------+---------------+
| 252-254 | Private Use | This document |
+---------+-------------+---------------+
| 255 | Reserved | This document |
+---------+-------------+---------------+
Table 10: SF Identifier Type
11. References
11.1. Normative References
[I-D.ietf-sfc-oam-packet]
Boucadair, M., "OAM Packet and Behavior in the Network
Service Header (NSH)", Work in Progress, Internet-Draft,
draft-ietf-sfc-oam-packet-03, 26 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-sfc-oam-
packet-03>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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[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>.
[RFC9015] Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L.
Jalil, "BGP Control Plane for the Network Service Header
in Service Function Chaining", RFC 9015,
DOI 10.17487/RFC9015, June 2021,
<https://www.rfc-editor.org/info/rfc9015>.
[RFC9145] Boucadair, M., Reddy.K, T., and D. Wing, "Integrity
Protection for the Network Service Header (NSH) and
Encryption of Sensitive Context Headers", RFC 9145,
DOI 10.17487/RFC9145, December 2021,
<https://www.rfc-editor.org/info/rfc9145>.
11.2. Informative References
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<https://www.rfc-editor.org/info/rfc792>.
[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005,
<https://www.rfc-editor.org/info/rfc4086>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[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>.
[RFC5706] Harrington, D., "Guidelines for Considering Operations and
Management of New Protocols and Protocol Extensions",
RFC 5706, DOI 10.17487/RFC5706, November 2009,
<https://www.rfc-editor.org/info/rfc5706>.
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[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437,
DOI 10.17487/RFC6437, November 2011,
<https://www.rfc-editor.org/info/rfc6437>.
[RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord,
"Return Path Specified Label Switched Path (LSP) Ping",
RFC 7110, DOI 10.17487/RFC7110, January 2014,
<https://www.rfc-editor.org/info/rfc7110>.
[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>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <https://www.rfc-editor.org/info/rfc7799>.
[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>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8595] Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based
Forwarding Plane for Service Function Chaining", RFC 8595,
DOI 10.17487/RFC8595, June 2019,
<https://www.rfc-editor.org/info/rfc8595>.
[RFC8924] Aldrin, S., Pignataro, C., Ed., Kumar, N., Ed., Krishnan,
R., and A. Ghanwani, "Service Function Chaining (SFC)
Operations, Administration, and Maintenance (OAM)
Framework", RFC 8924, DOI 10.17487/RFC8924, October 2020,
<https://www.rfc-editor.org/info/rfc8924>.
[RFC9263] Wei, Y., Ed., Elzur, U., Majee, S., Pignataro, C., and D.
Eastlake 3rd, "Network Service Header (NSH) Metadata Type
2 Variable-Length Context Headers", RFC 9263,
DOI 10.17487/RFC9263, August 2022,
<https://www.rfc-editor.org/info/rfc9263>.
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Contributors' Addresses
Cui Wang
Individual contributor
Email: lindawangjoy@xxxxxxxxx
Zhonghua Chen
China Telecom
No.1835, South PuDong Road
Shanghai
201203
China
Phone: +86 18918588897
Email: chenzhongh@xxxxxxxxxxxxxxx
Authors' Addresses
Greg Mirsky
Ericsson
Email: gregimirsky@xxxxxxxxx
Wei Meng
ZTE Corporation
No.50 Software Avenue, Yuhuatai District
Nanjing,
China
Email: meng.wei2@xxxxxxxxxx
Ting Ao
China Mobile
No.889, BiBo Road
Shanghai
201203
China
Phone: +86 17721209283
Email: 18555817@xxxxxx
Bhumip Khasnabish
Individual contributor
Email: vumip1@xxxxxxxxx
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Kent Leung
Individual contributor
530 Showers Drive Ste 7
Mountain View, CA 94040,
United States of America
Email: mail4kentl@xxxxxxxxx
Gyan Mishra
Verizon Inc.
Email: gyan.s.mishra@xxxxxxxxxxx
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