Internet Engineering Task Force (IETF) G. Mirsky
Request for Comments: 9516 Ericsson
Category: Standards Track W. Meng
ISSN: 2070-1721 ZTE Corporation
T. Ao
China Mobile
B. Khasnabish
K. Leung
Individual Contributor
G. Mishra
Verizon Inc.
November 2023
Active Operations, Administration, and Maintenance (OAM) for Service
Function Chaining (SFC)
Abstract
A set of requirements for active Operations, Administration, and
Maintenance (OAM) for Service Function Chaining (SFC) 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 is an Internet Standards Track document.
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). Further information on
Internet Standards is available in 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/rfc9516.
Copyright Notice
Copyright (c) 2023 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
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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
2. Terminology and Conventions
2.1. Requirements Language
2.2. Acronyms
3. Requirements for Active OAM in SFC
4. Active OAM Identification in the NSH
5. SFC Active OAM Header
6. Echo Request/Reply for SFC
6.1. Return Codes
6.2. Authentication in Echo Request/Reply
6.3. SFC Echo Request Transmission
6.3.1. Source ID TLV
6.4. Processing a Received SFC Echo Request
6.4.1. Errored TLVs TLV
6.5. SFC Echo Reply Transmission
6.5.1. Reply Service Function Path TLV
6.5.2. Theory of Operation
6.5.3. SFC Echo Reply Reception
6.5.4. Tracing an SFP
6.6. The Use of the Consistency Verification Request Message
6.6.1. SFF Information Record TLV
6.6.2. SF Information Sub-TLV
6.6.3. SF Information Sub-TLV Construction
7. Security Considerations
8. Operational Considerations
9. IANA Considerations
9.1. SFC Active OAM Protocol
9.2. SFC Active OAM
9.2.1. SFC Active OAM Message Types
9.2.2. SFC Echo Request Flags
9.2.3. SFC Echo Types
9.2.4. SFC Echo Reply Modes
9.2.5. SFC Echo Return Codes
9.2.6. SFC Active OAM TLV Types
9.2.7. SF Identifier Types
10. References
10.1. Normative References
10.2. Informative References
Acknowledgments
Contributors
Authors' Addresses
1. Introduction
[RFC7665] defines data plane elements necessary to implement Service
Function Chaining (SFC). These include the following:
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 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 the 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], an SFP is the instantiation of SFC in the network and
provides a level of indirection between the entirely abstract SFCs
and a fully specified, ordered list of SFF and SF identities that the
packet will visit when it traverses SFC. The latter entity is
referred to as Rendered Service Path (RSP). The main difference
between an 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 Operations, Administration, and
Maintenance (OAM), per the definition of active OAM in [RFC7799], is
implemented when the 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 tools that are conformant to this specification improve
OAM's ability for Fault Management (FM) by, for example, using the
query mechanism to troubleshoot and localize defects, which conforms
to the stateless character of transactions in SFC NSH [RFC8300].
Note that Performance Monitoring OAM, as required by [RFC8924], is
not satisfied by this document and is out of scope. For the purpose
of FM OAM in SFC, the SFC Echo Request and Echo Reply are specified
in Section 6. These mechanisms enable on-demand continuity check and
connectivity verification, among other operations, over SFC in
networks and address functionalities discussed in Sections 4.1, 4.2,
and 4.3 of [RFC8924]. The SFC Echo Request and Echo Reply can be
used with encapsulations other than the NSH, for example, using MPLS
encapsulation, as described in [RFC8595]. The applicability of the
SFC Echo Request/Reply mechanism in SFC encapsulations other than the
NSH is outside the scope of this document.
The intended scope of SFC active OAM is for use within a single
provider's operational domain. The SFC active OAM deployment scope
is deliberately constrained, as explained in [RFC7665] and [RFC8300],
and limited to a single network administrative domain.
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. Additionally, "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
MAC: Message Authentication Code
NSH: Network Service Header
OAM: Operations, Administration, and Maintenance
RSP: Rendered Service Path
SF: Service Function
SFC: Service Function Chaining
SFF: Service Function Forwarder
SFI: Service Function Instance
SFP: Service Function Path
3. Requirements for Active OAM in SFC
As discussed in [RFC8924], SFC-specific means are needed to perform
the FM OAM task 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 Service Function Instances (SFIs) of the same SF.
End-to-End (E2E) SFC OAM has the Classifier as the ingress and SFF3
as its egress. The scope of Segment SFC OAM is between two elements
that are part of the same SFP. The following are the requirements
for an FM SFC OAM, whether with the E2E or segment scope:
REQ1: Packets of SFC active 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.
REQ2: 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 predetermined time. For example,
in the E2E FM SFC OAM case, i.e., the egress, SFF3 (Figure 1) could
be the entity that detects the SFP's failure by 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:
REQ3: SFC OAM MUST support Remote Defect Indication notification by
the egress to the ingress.
REQ4: SFC OAM MUST support connectivity verification of the SFP.
The definitions of the misconnection defect, entry, and exit
criteria are outside the scope of this document.
Once an SFF detects the defect, the objective of the SFC OAM changes
from the detection of a defect to defect characterization and
localization.
REQ5: SFC OAM MUST support fault localization of the loss of
continuity check within an SFP.
REQ6: SFC OAM MUST support an SFP tracing to discover the RSP.
In the example presented in Figure 1, two distinct instances of the
same SF share the same SFF. In this example, the SFP can be realized
over several RSPs that use different instances of the 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 of [RFC8924] or the procedure defined in
Section 6.5.4.
REQ7: 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, an SFF can act as a proxy for another element within
the service function chain.
REQ8: SFC OAM MUST be able to trigger on-demand FM remotely with
responses being directed toward the initiator of the remote
request.
The conformance of the SFC Echo Request/Reply mechanism to these
requirements is reflected below:
REQ1: Fate sharing via the SFC Echo Request/Reply defined in
Section 6.
REQ2: Continuity monitoring via the SFP tracing defined in
Section 6.5.4.
REQ3: Remote defect detection via the SFC Echo Request/Reply defined
in Section 6.
REQ4: Connectivity verification via the SFP tracing defined in
Section 6.5.4.
REQ5: Fault localization via verification of the SFP consistency
defined in Section 6.6.
REQ6: SFP tracing as described in Section 6.5.4 and verification of
SFP consistency as defined in Section 6.6.
REQ7: Discover and exercise available RSPs via trace defined in
Section 6.5.4.
REQ8: Can be addressed by adding the proxying capability to the SFC
Echo Request/Reply described in this document. [RFC7555]
describes an example of a proxy function for an Echo Request.
Specification of a proxy function for SFC Echo Request is
outside the scope of this document.
4. Active OAM Identification in the NSH
SFC active OAM combines OAM commands and/or data included in a
message that immediately follows the NSH. To identify the SFC active
OAM message, the Next Protocol field MUST be set to SFC Active OAM
(0x07) (Section 9.1). The O bit in the NSH MUST be set, according to
[RFC9451]. A case when the O bit is clear and the Next Protocol
field value is set to SFC Active OAM (0x07) is considered an
erroneous combination. An implementation MUST report it. Although
the notification mechanism is outside the scope of this
specification, note that it MUST include rate-limiting control. The
packet SHOULD be dropped. An implementation MAY have control to
enable the processing of the OAM payload.
5. SFC Active OAM Header
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 an extra
IP/UDP header, especially in an IPv6 network, adds overhead compared
to the length of an Active OAM Control Packet (e.g., BFD Control
packet [RFC5880]). In some environments, for example, when measuring
performance metrics, it is beneficial to transmit OAM packets in a
broad range of lengths to emulate application traffic closer. This
document defines an Active OAM Header (Figure 2) to demultiplex
active OAM protocols on 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 | Reserved | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SFC Active OAM Control Packet ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SFC Active OAM Header
V - a four-bit field that 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 - a six-bit field that identifies the OAM protocol, e.g.,
the Echo Request/Reply.
Reserved - a six-bit field. It MUST be zeroed on transmission and
ignored on receipt.
Length - a two-octet field that is the length of the SFC Active OAM
Control Packet in octets.
6. Echo Request/Reply for SFC
The 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 MPLS [RFC8029] are examples of
broadly used active OAM protocols based on the Echo Request/Reply
principle. The SFC Echo Request/Reply control message (format is
presented in Figure 3) is an instance of the SFC Active OAM Control
Packet that is a part of the SFC Active OAM Header (Figure 2).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Echo Request Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Echo 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:
Echo Request Flags - a two-octet bit vector field. Section 9.2.2
requests IANA to create a new registry for flags. This
specification defines all flags for future use. Flags MUST be
zeroed on transmission and ignored on receipt.
Reserved - a two-octet field. It MUST be zeroed on transmission and
ignored on receipt.
Echo Type - a one-octet field that reflects the packet type. SFC
Echo Request/Reply Echo Types, defined in this document, are
listed in Section 9.2.3.
Reply Mode - a one-octet field. It defines the type of the return
path requested by the sender of the Echo Request.
Return Code and Return Subcode - one-octet fields each. These can
be used to inform the sender about the result of processing its
request. For all Return Code values defined in this document
(Section 9.2.5), the value of the Return Subcode field MUST be set
to zero.
Sender's Handle - 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 being sent). The sender of the Echo
Request SHOULD use a pseudorandom number generator [RFC4086] to
set the value of the Sender's Handle field. In some use cases, an
implementation MAY use the Sender's Handle for proprietary
signaling as long as the system that receives the SFC Echo Request
doesn't alter the value of the Sender's Handle field but copies it
into the SFC Echo Reply.
Sequence Number - a four-octet field. It is assigned by the sender
and can be, for example, used to detect missed replies. The
initial Sequence Number contains an unsigned integer that wraps
around. It MUST be pseudorandomly generated [RFC4086] and then
SHOULD be monotonically increasing in the course of the test
session. If a reply is sent, the sender of the SFC Echo Reply
message MUST copy the value from the received SFC Echo Request.
TLV is a variable-length construct whose length is multiple four-
octet words. 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. If
no TLVs are included in an SFC Echo Request/Reply, the value of the
Length field in the SFC Active OAM Header MUST be 16 octets.
Figure 4 presents the format of an SFC Echo Request/Reply TLV, where
the fields are defined as follows:
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 9.2.6.
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 MUST set it to
one of the values in IANA's "SFC Echo Return Codes" registry
(Section 9.2.5) in the corresponding Echo Reply that it generates.
6.2. Authentication in Echo Request/Reply
Authentication can be used to protect the integrity of the
information in the SFC Echo Request and/or Echo Reply. In [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. The MAC#1 Context
Header is more suitable for the integrity protection of SFC active
OAM, particularly of the SFC Echo Request and Echo Reply, as defined
in this document. On the other hand, using the MAC#2 Context Header
allows the detection of mishandling of the O bit by a transient SFC
element.
6.3. SFC Echo Request Transmission
The SFC Echo Request control packet MUST use the appropriate underlay
network encapsulation of the monitored SFP. The Echo Request MUST
set the O bit in the NSH, as defined in [RFC9451]. The NSH MUST be
immediately followed by the SFC Active OAM Header defined in
Section 4. The Echo Type field's value in the SFC Active OAM Header
MUST be set to the SFC Echo Request/Reply value (1), per
Section 9.2.1.
The value of the Reply Mode field MUST be set to one of the
following:
Do Not Reply (1) - This is the value 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) - If an SFC Echo Request is
not encapsulated in IP/UDP, then this value requests the use of
the Source ID TLV Section 6.3.1).
Reply via Specified Path (4) - This value requests the use of the
particular return path specified in the included TLV to verify
bidirectional 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 Specified Path with the data integrity protection (7) -
This value requests the use of the MAC Context Header [RFC9145].
6.3.1. Source ID TLV
The responder to the SFC Echo Request encapsulates the SFC Echo Reply
message in the IP/UDP packet if the Reply Mode is "Reply via an IPv4/
IPv6 UDP Packet" or "Reply via an IPv4/IPv6 UDP Packet with the data
integrity protection". Because the NSH does not identify the ingress
node that generated the Echo Request, information that sufficiently
identifies the source MUST be included in the message so that the IP
destination address and destination UDP port number for IP/UDP
encapsulation of the SFC Echo Reply could be derived. The sender of
the SFC Echo Request MUST include the Source ID TLV (Figure 5).
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 ID TLV
The fields are defined as follows:
Source ID - the value MUST be set to 1 (Section 9.2.6).
Reserved1 - a one-octet field. The field MUST be zeroed on
transmission and ignored on receipt.
Length - 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 ID
TLV is considered to be malformed.
Port Number - 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 - a two-octet field. The field MUST be zeroed on transmit
and ignored on receipt.
IP Address - a field that contains the IP address of the sender of
the SFC OAM control message, i.e., 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 ID 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. The source IP address used in the IP/UDP
encapsulation of the SFC Echo Reply is one of the IP addresses
associated with the responder. The value of the Port Number field
MUST be used as the destination UDP port number in the IP/UDP
encapsulation of the SFC Echo Reply message. The responder selects
the source UDP port number from the dynamic range of port numbers.
If more than one Source ID TLV per the address family is present, the
receiver MUST use the first TLV and ignore the rest. The Echo Reply
message, including relevant TLVs, follows the IP/UDP headers
immediately.
6.4. Processing a Received SFC Echo Request
Punting a received SFC Echo Request to the control plane for
validation and processing is triggered by one of the following packet
processing exceptions: NSH TTL expiration, NSH Service Index
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.
1.1. Suppose the authentication validation has failed and the
Source ID TLV is considered properly formatted. In that
case, the SFF MUST send an SFC Echo Reply with the Return
Code set to 3 ("Authentication failed") and the Subcode set
to zero to the system identified in the Source ID TLV (see
Section 6.5), according to a rate-limit control mechanism.
1.2. If the authentication is validated successfully, the SFF
that has received an SFC Echo Request verifies the rest of
the packet's general consistency.
2. Validate the Source ID TLV, as defined in Section 6.3.1.
2.1. If the Source ID TLV is determined to be 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.
3. The Sender's Handle and Sequence Number fields are not examined
but are copied in the SFC Echo Reply message.
4. If the packet is not well formed, i.e., not formed according to
this specification, the receiving SFF SHOULD send an SFC Echo
Reply with the Return Code set to 1 ("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 ID
TLV (see Section 6.5).
5. 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 of the 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.
6. If the consistency check of the received Echo Request succeeded,
i.e., the Echo Request is deemed properly formed, then the SFF at
the end of the SFP MUST send an SFC Echo Reply with the Return
Code set to 5 ("End of the SFP") and the Subcode set to zero.
7. If the SFF is not at the end of the SFP and the NSH TTL value is
1, the SFF MUST send an SFC Echo Reply with the Return Code set
to 4 ("SFC TTL Exceeded") and the Subcode set to zero.
8. In all other cases, for the validated Echo Request message, a
transit, i.e., not at the end of the SFP, SFF MUST send an SFC
Echo Reply with the Return Code set to 0 ("No Error") 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 of the 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
The fields are defined as follows:
Errored TLVs - the field MUST be set to 2 (Section 9.2.6).
Reserved - the field MUST be zeroed on transmission and ignored on
receipt.
Length - the value equals to length of the Value field in octets.
Value - the field contains the TLVs, encoded as sub-TLVs (as shown
in Figure 7), that were not understood or failed to be parsed
correctly.
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 a Sub-TLV
The fields are defined as follows:
Sub-TLV Type - a copy of the first octet of the TLV that is not
understood or failed to be parsed.
Reserved - MUST be zeroed on transmission and ignored on receipt.
Sub-TLV Length - the value equals the value of the Length field of
the errored TLV.
Sub-TLV Value - the field contains data that follows 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.
For example, a TLV that specifies the return path of the Echo Reply
if the Return Mode in the Echo Request is set to Reply via Specified
Path (4) is described in Section 6.5.1. Value 1 is the "Do Not
Reply" mode and suppresses the Echo Reply packet transmission. The
value 2 of the Reply Mode field requests sending the Echo Reply
packet out-of-band as an IPv4/IPv6 UDP packet.
6.5.1. Reply Service Function Path TLV
While the SFC Echo Request always traverses the SFP it is directed to
by using the NSH, the corresponding Echo Reply usually is sent
without the NSH. In some cases, an operator might choose to direct
the responder to send and Echo Reply with the NSH over a particular
SFP. This section defines a new TLV, i.e., Reply Service Function
Path TLV, for Reply via Specified Path mode of the SFC Echo Reply.
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 of [RFC7665]. For example, it allows an
operator to test both directions of the bidirectional or hybrid SFP
with a single SFC Echo Request/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
The fields are defined as follows:
Reply SFP (3) - identifies the TLV that contains information about
the SFC Reply path.
Reserved - MUST be zeroed on transmission and ignored on receipt.
Length - the value MUST be equal to 4.
Reply Service Function Path Identifier - a three-octet field that
contains the SFP identifier for the path that the SFC Echo Reply
message is requested to be sent over.
Service Index - a one-octet field. The value is set to the value of
the Service Index field in the NSH of the SFC Echo Reply message.
6.5.2. Theory of Operation
[RFC7110] defines a mechanism to control the return path for the MPLS
Label Switched Path (LSP) Echo Reply. In the 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.
When sending an Echo Request, the sender MUST set the value of the
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 the 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, as defined in Section 6.4.
The destination SFF of the SFP being tested and the SFF at which the
NSH TTL expired (as per [RFC8300]) are referred to as responding
SFFs. The processing described below equally applies to both cases.
If the Echo Request message with the Reply Service Function Path TLV
received by the responding SFF has the Reply Mode value of "Reply via
Specified Path" but no Reply Service Function Path TLV is present,
then the responding SFF MUST send an Echo Reply with the Return Code
set to 6 ("Reply Service Function Path TLV is missing"). If the
responding SFF cannot find the requested SFP, it MUST send an Echo
Reply with the 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 Code field to 8
("Unverifiable Reply Service Function Path"). The receiver MAY drop
the Echo Request when it cannot determine whether the SFP's return
path has the route to the initiator. When sending the 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. Bidirectional SFC Case
The ability to specify the return path for an Echo Reply might be
used in the case of bidirectional 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
SFC. Because of that, even for bidirectional SFC, a reverse SFP
needs to be indicated in a Reply Service Function Path TLV in the
Echo Request message.
6.5.3. SFC Echo Reply Reception
An SFF SHOULD NOT accept the 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;
* the Sequence Number in the Echo Reply received matches the
Sequence Number of one of the outstanding transmitted Echo
Requests; and
* all other checks passed.
6.5.4. Tracing an SFP
The SFC Echo Request/Reply can be used to isolate a defect detected
in the SFP and trace an RSP. As with the ICMP Echo Request/Reply
[RFC0792] and the 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 Multipath 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. The Use of the Consistency Verification Request Message
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 Echo Request/Reply message
(Figure 3). The sender of an SFP Consistency Verification Request
(CVReq) message MUST set the value of the SFC Echo Request/Reply Echo
Type field to 3 ("SFP Consistency Verification Request"). The sender
of an SFP Consistency Verification Reply (CVRep) message MUST set the
value of the SFC Echo Request/Reply Echo Type field to 4 ("SFP
Consistency Verification Reply"). All processing steps of SFC Echo
Request and Echo Reply messages described in Sections 6.3 through 6.5
apply to the processing of CVReq and CVRep, respectively.
Every SFF that receives a CVReq message MUST perform the following
actions:
* Collect information about the SFs traversed by the CVReq packet
and send it to the ingress SFF as a CVRep packet over an IP
network.
* Forward the CVReq to the next downstream SFF if the one exists.
As a result, the ingress SFF collects information about all traversed
SFFs and SFs, i.e., 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. SFF Information Record TLV
For the received CVReq, an SFF that supports this specification MUST
include in the CVRep message the information about SFs that are
available from that SFF instance for the specified SFP. The SFF MUST
include the SFF Information Record TLV (Figure 9) in the 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 6.6.2).
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 |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 the fields are defined as follows:
SFF Record TLV - the value is (4) (Section 9.2.6).
Reserved - MUST be zeroed on transmission and ignored on receipt.
Length - the value equals the sum of lengths of the Service Path
Identifier, reserved, and SF Information Sub-TLV fields in octets.
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 Section 6.6.2.
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.
6.6.2. 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 |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Service Function Information Sub-TLV
SF Sub-TLV - one-octet field. The value is (5) (Section 9.2.6).
Reserved - one-octet field. The field MUST be zeroed on
transmission and ignored on receipt.
Length - two-octet 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 in
Section 9.2.7.
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.
6.6.3. 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 the SFP, only
one SF Information Sub-TLV is included in the CVRep. If several SFs
are attached to the SFF in the SFP, the SF Information Sub-TLV MUST
be constructed as described below in either Section 6.6.3.1 or
6.6.3.2.
6.6.3.1. 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. SF1, SF2, and SF3 are attached to SFF1, and SF4
is attached to SFF2. The CVReq message is sent to the SFFs in 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
6.6.3.2. 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
the respective SF Identifiers will be listed sequentially in the SF
Identifier field of the Service Function Information 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)
Figure 12: Example 2 for CVRep with Multiple SFs
7. Security Considerations
As an element of SFC OAM and, specifically, based on the NSH, the
Echo Request/Reply mechanism described in this document inherits
security considerations discussed in [RFC7665] and [RFC8300].
When the integrity protection for SFC active OAM, particularly the
SFC Echo Request/Reply, is required, using one of the Context Headers
defined in [RFC9145] is RECOMMENDED. The MAC#1 Context Header could
be more suitable for SFC active OAM because it does not require
recalculation 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, i.e., an IP
Authentication Header [RFC4302] or IP Encapsulating Security Payload
Header [RFC4303], it 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 the 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, i.e., sending SFC Echo Requests to
overload an element of SFC. The second may use spoofing, hijacking,
replying, or otherwise tampering with SFC Echo Requests and/or
Replies to misrepresent and 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/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 MUST have means
to check that the source of the Echo Request is part of the SFP.
Also, since the SF Information Sub-TLV discloses information about
the SFP, the spoofed CVReq packet may be used to obtain network
information. Thus, implementations MUST provide a means of checking
the source addresses of CVReq messages, as specified in Section 6.3.1
("Source ID TLV"), 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].
The SFC NSH Echo Request/Reply provides essential OAM functions for
network operators. The SFC NSH Echo Request/Reply is intended to
detect and localize defects in 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 SFC
active OAM will discard the protocol's packets. If SFC uses a
reclassification along the SFP or when the principle of load
balancing is unknown, the fate sharing between data and active OAM
packets cannot be guaranteed. As a result, the OAM outcome might not
reflect the state of the entire SFC properly but only its segment.
In general, it is an operational task to consider the cases where
active OAM may not share fate with the monitored SFP. The 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 that is structured or standardized.
9. IANA Considerations
The terms used in the IANA considerations below are intended to be
consistent with [RFC8126].
9.1. SFC Active OAM Protocol
IANA has assigned the following new type in the "NSH Next Protocol"
registry within the "Network Service Header (NSH) Parameters" group
of registries:
+===============+================+===========+
| Next Protocol | Description | Reference |
+===============+================+===========+
| 0x07 | SFC Active OAM | RFC 9516 |
+---------------+----------------+-----------+
Table 1: SFC Active OAM Protocol
9.2. SFC Active OAM
IANA has created the "Service Function Chaining (SFC) Active
Operations, Administration, and Maintenance (OAM)" group of
registries, which contains the registries described in the following
subsections.
9.2.1. SFC Active OAM Message Types
IANA has created the "SFC Active OAM Message Types" registry as
follows:
Registry Name: SFC Active OAM Message Types
Assignment Policy:
0 - 31 IETF Review
32 - 62 First Come First Served
Reference: RFC 9516
+========+========================+===========+
| Value | Description | Reference |
+========+========================+===========+
| 0 | Reserved | RFC 9516 |
+--------+------------------------+-----------+
| 1 | SFC Echo Request/Reply | RFC 9516 |
+--------+------------------------+-----------+
| 2 - 62 | Unassigned | |
+--------+------------------------+-----------+
| 63 | Reserved | RFC 9516 |
+--------+------------------------+-----------+
Table 2: SFC Active OAM Message Types
9.2.2. SFC Echo Request Flags
IANA has created the "SFC Echo Request Flags" registry to track the
assignment of the 16 flags in the SFC Echo Request Flags field of the
SFC Echo Request message. The flags are numbered from 0 (the most
significant bit is transmitted first) to 15.
IANA has created the "SFC Echo Request Flags" registry as follows:
Registry Name: SFC Echo Request Flags
Assignment Policy:
0 - 15 Standards Action
Reference:
RFC 9516
+============+=============+===========+
| Bit Number | Description | Reference |
+============+=============+===========+
| 0 - 15 | Unassigned | |
+------------+-------------+-----------+
Table 3: SFC Echo Request Flags
9.2.3. SFC Echo Types
IANA has created the "SFC Echo Types" registry as follows:
Registry Name: SFC Echo Types
Assignment Policy:
0 - 175 IETF Review
176 - 239 First Come First Served
240 - 251 Experimental Use
252 - 254 Private Use
Reference: RFC 9516
+===========+======================================+===========+
| Value | Description | Reference |
+===========+======================================+===========+
| 0 | Reserved | RFC 9516 |
+-----------+--------------------------------------+-----------+
| 1 | SFC Echo Request | RFC 9516 |
+-----------+--------------------------------------+-----------+
| 2 | SFC Echo Reply | RFC 9516 |
+-----------+--------------------------------------+-----------+
| 3 | SFP Consistency Verification Request | RFC 9516 |
+-----------+--------------------------------------+-----------+
| 4 | SFP Consistency Verification Reply | RFC 9516 |
+-----------+--------------------------------------+-----------+
| 5 - 239 | Unassigned | |
+-----------+--------------------------------------+-----------+
| 240 - 251 | Reserved for Experimental Use | RFC 9516 |
+-----------+--------------------------------------+-----------+
| 252 - 254 | Reserved for Private Use | RFC 9516 |
+-----------+--------------------------------------+-----------+
| 255 | Reserved | RFC 9516 |
+-----------+--------------------------------------+-----------+
Table 4: SFC Echo Types
9.2.4. SFC Echo Reply Modes
IANA has created the "SFC Echo Reply Modes" registry as follows:
Registry Name: SFC Echo Reply Modes
Assignment Policy:
0 - 175 IETF Review
176 - 239 First Come First Served
240 - 251 Experimental Use
252 - 254 Private Use
Reference: RFC 9516
+=======+====================================+===========+
| Value | Description | Reference |
+=======+====================================+===========+
| 0 | Reserved | RFC 9516 |
+-------+------------------------------------+-----------+
| 1 | Do Not Reply | RFC 9516 |
+-------+------------------------------------+-----------+
| 2 | Reply via an IPv4/IPv6 UDP Packet | RFC 9516 |
+-------+------------------------------------+-----------+
| 3 | Unassigned | |
+-------+------------------------------------+-----------+
| 4 | Reply via Specified Path | RFC 9516 |
+-------+------------------------------------+-----------+
| 5 | Reply via an IPv4/IPv6 UDP Packet | RFC 9516 |
| | with the data integrity protection | |
+-------+------------------------------------+-----------+
| 6 | Unassigned | |
+-------+------------------------------------+-----------+
| 7 | Reply via Specified Path with the | RFC 9516 |
| | data integrity protection | |
+-------+------------------------------------+-----------+
| 8 - | Unassigned | |
| 239 | | |
+-------+------------------------------------+-----------+
| 240 - | Reserved for Experimental Use | RFC 9516 |
| 251 | | |
+-------+------------------------------------+-----------+
| 252 - | Reserved for Private Use | RFC 9516 |
| 254 | | |
+-------+------------------------------------+-----------+
| 255 | Reserved | RFC 9516 |
+-------+------------------------------------+-----------+
Table 5: SFC Echo Reply Modes
9.2.5. SFC Echo Return Codes
IANA has created the "SFC Echo Return Codes" registry as follows:
Registry Name: SFC Echo Return Codes
Assignment Policy:
0 - 191 IETF Review
192 - 251 First Come First Served
252 - 254 Private Use
Reference: RFC 9516
+=========+============================================+===========+
| Value | Description | Reference |
+=========+============================================+===========+
| 0 | No Error | RFC 9516 |
+---------+--------------------------------------------+-----------+
| 1 | Malformed Echo Request received | RFC 9516 |
+---------+--------------------------------------------+-----------+
| 2 | One or more of the TLVs was not understood | RFC 9516 |
+---------+--------------------------------------------+-----------+
| 3 | Authentication failed | RFC 9516 |
+---------+--------------------------------------------+-----------+
| 4 | SFC TTL Exceeded | RFC 9516 |
+---------+--------------------------------------------+-----------+
| 5 | End of the SFP | RFC 9516 |
+---------+--------------------------------------------+-----------+
| 6 | Reply Service Function Path TLV is missing | RFC 9516 |
+---------+--------------------------------------------+-----------+
| 7 | Reply SFP was not found | RFC 9516 |
+---------+--------------------------------------------+-----------+
| 8 | Unverifiable Reply Service Function Path | RFC 9516 |
+---------+--------------------------------------------+-----------+
| 9 - 251 | Unassigned | |
+---------+--------------------------------------------+-----------+
| 252 - | Reserved for Private Use | RFC 9516 |
| 254 | | |
+---------+--------------------------------------------+-----------+
| 255 | Reserved | RFC 9516 |
+---------+--------------------------------------------+-----------+
Table 6: SFC Echo Return Codes
9.2.6. SFC Active OAM TLV Types
IANA has created the "SFC Active OAM TLV Types" registry as follows:
Registry Name: SFC Active OAM TLV Types
Assignment Policy:
0 - 175 IETF Review
176 - 239 First Come First Served
240 - 251 Experimental Use
252 - 254 Private Use
Reference: RFC 9516
+===========+==================================+===========+
| Value | Description | Reference |
+===========+==================================+===========+
| 0 | Reserved | RFC 9516 |
+-----------+----------------------------------+-----------+
| 1 | Source ID TLV | RFC 9516 |
+-----------+----------------------------------+-----------+
| 2 | Errored TLVs | RFC 9516 |
+-----------+----------------------------------+-----------+
| 3 | Reply Service Function Path Type | RFC 9516 |
+-----------+----------------------------------+-----------+
| 4 | SFF Information Record Type | RFC 9516 |
+-----------+----------------------------------+-----------+
| 5 | SF Information | RFC 9516 |
+-----------+----------------------------------+-----------+
| 6 - 239 | Unassigned | |
+-----------+----------------------------------+-----------+
| 240 - 251 | Reserved for Experimental Use | RFC 9516 |
+-----------+----------------------------------+-----------+
| 252 - 254 | Reserved for Private Use | RFC 9516 |
+-----------+----------------------------------+-----------+
| 255 | Reserved | RFC 9516 |
+-----------+----------------------------------+-----------+
Table 7: SFC Active OAM TLV Types
9.2.7. SF Identifier Types
IANA has created the "SF Identifier Types" as follows:
Registry Name: SF Identifier Types
Assignment Policy:
0 - 191 IETF Review
192 - 251 First Come First Served
252 - 254 Private Use
Reference: RFC 9516
+===========+==========================+===========+
| Value | Description | Reference |
+===========+==========================+===========+
| 0 | Reserved | RFC 9516 |
+-----------+--------------------------+-----------+
| 1 | IPv4 | RFC 9516 |
+-----------+--------------------------+-----------+
| 2 | IPv6 | RFC 9516 |
+-----------+--------------------------+-----------+
| 3 | MAC | RFC 9516 |
+-----------+--------------------------+-----------+
| 4 - 251 | Unassigned | |
+-----------+--------------------------+-----------+
| 252 - 254 | Reserved for Private Use | RFC 9516 |
+-----------+--------------------------+-----------+
| 255 | Reserved | RFC 9516 |
+-----------+--------------------------+-----------+
Table 8: SF Identifier Types
10. References
10.1. Normative References
[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>.
[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>.
[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>.
[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>.
[RFC9451] Boucadair, M., "Operations, Administration, and
Maintenance (OAM) Packet and Behavior in the Network
Service Header (NSH)", RFC 9451, DOI 10.17487/RFC9451,
August 2023, <https://www.rfc-editor.org/info/rfc9451>.
10.2. 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>.
[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>.
[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>.
[RFC7555] Swallow, G., Lim, V., and S. Aldrin, "Proxy MPLS Echo
Request", RFC 7555, DOI 10.17487/RFC7555, June 2015,
<https://www.rfc-editor.org/info/rfc7555>.
[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>.
Acknowledgments
The authors greatly appreciate the thorough review and the most
helpful comments from Dan Wing, Dirk von Hugo, Mohamed Boucadair,
Donald Eastlake 3rd, 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. The authors greatly appreciate the
thoroughness of comments and thoughtful suggestions by Darren Dukes
that significantly improved the document.
Contributors
Cui Wang
Individual contributor
Email: lindawangjoy@gmail.com
Zhonghua Chen
China Telecom
No.1835, South PuDong Road
Shanghai
201203
China
Phone: +86 18918588897
Email: chenzhongh@chinatelecom.cn
Authors' Addresses
Greg Mirsky
Ericsson
Email: gregimirsky@gmail.com
Wei Meng
ZTE Corporation
Yuhuatai District
No.50 Software Avenue
Nanjing,
China
Email: meng.wei2@zte.com.cn
Ting Ao
China Mobile
No.889, BiBo Road
Shanghai
201203
China
Phone: +86 17721209283
Email: 18555817@qq.com
Bhumip Khasnabish
Individual Contributor
Email: vumip1@gmail.com
Kent Leung
Individual Contributor
530 Showers Drive Ste 7
Mountain View, CA 94040
United States of America
Email: mail4kentl@gmail.com
Gyan Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com