Internet Engineering Task Force (IETF) F. Brockners, Ed.

Internet Engineering Task Force (IETF) F. Brockners, Ed.
Request for Comments: 9378 Cisco
Category: Informational S. Bhandari, Ed.
ISSN: 2070-1721 Thoughtspot
D. Bernier
Bell Canada
T. Mizrahi, Ed.
Huawei
April 2023

In Situ Operations, Administration, and Maintenance (IOAM) Deployment

Abstract

In situ Operations, Administration, and Maintenance (IOAM) collects
operational and telemetry information in the packet while the packet
traverses a path between two points in the network. This document
provides a framework for IOAM deployment and provides IOAM deployment
considerations and guidance.

Status of This Memo

This document is not an Internet Standards Track specification; it is
published for informational purposes.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9378.

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Table of Contents

1. Introduction
2. Conventions
3. IOAM Deployment: Domains and Nodes
4. Types of IOAM
4.1. Per-Hop Tracing IOAM
4.2. Proof of Transit IOAM
4.3. E2E IOAM
4.4. Direct Export IOAM
5. IOAM Encapsulations
5.1. IPv6
5.2. NSH
5.3. BIER
5.4. GRE
5.5. Geneve
5.6. Segment Routing
5.7. Segment Routing for IPv6
5.8. VXLAN-GPE
6. IOAM Data Export
7. IOAM Deployment Considerations
7.1. IOAM-Namespaces
7.2. IOAM Layering
7.3. IOAM Trace Option-Types
7.4. Traffic-Sets That IOAM Is Applied To
7.5. Loopback Flag
7.6. Active Flag
7.7. Brown Field Deployments: IOAM-Unaware Nodes
8. IOAM Manageability
9. IANA Considerations
10. Security Considerations
11. Informative References
Acknowledgements
Authors' Addresses

1. Introduction

In situ Operations, Administration, and Maintenance (IOAM) collects
OAM information within the packet while the packet traverses a
particular network domain. The term "in situ" refers to the fact
that the OAM data is added to the data packets rather than being sent
within packets specifically dedicated to OAM. IOAM complements
mechanisms such as Ping, Traceroute, or other active probing
mechanisms. In terms of "active" or "passive" OAM, IOAM can be
considered a hybrid OAM type. In situ mechanisms do not require
extra packets to be sent. IOAM adds information to the already
available data packets and, therefore, cannot be considered passive.
In terms of the classification given in [RFC7799], IOAM could be
portrayed as Hybrid Type I. IOAM mechanisms can be leveraged where
mechanisms using, e.g., ICMP do not apply or do not offer the desired
results. These situations could include:

* proving that a certain traffic flow takes a predefined path,

* verifying the Service Level Agreement (SLA) verification for the
live data traffic,

* providing detailed statistics on traffic distribution paths in
networks that distribute traffic across multiple paths, or

* providing scenarios in which probe traffic is potentially handled
differently from regular data traffic by the network devices.

2. Conventions

Abbreviations used in this document:

BIER: Bit Index Explicit Replication [RFC8279]

Geneve: Generic Network Virtualization Encapsulation [RFC8926]

GRE: Generic Routing Encapsulation [RFC2784]

IOAM: In situ Operations, Administration, and Maintenance

MTU: Maximum Transmission Unit

NSH: Network Service Header [RFC8300]

OAM: Operations, Administration, and Maintenance

POT: Proof of Transit

VXLAN-GPE: Virtual eXtensible Local Area Network - Generic Protocol
Extension [VXLAN-GPE]

3. IOAM Deployment: Domains and Nodes

[RFC9197] defines the scope of IOAM as well as the different types of
IOAM nodes. For improved readability, this section provides a brief
overview of where IOAM applies, along with explaining the main roles
of nodes that employ IOAM. Please refer to [RFC9197] for further
details.

IOAM is focused on "limited domains", as defined in [RFC8799]. IOAM
is not targeted for a deployment on the global Internet. The part of
the network that employs IOAM is referred to as the "IOAM-Domain".
For example, an IOAM-Domain can include an enterprise campus using
physical connections between devices or an overlay network using
virtual connections or tunnels for connectivity between said devices.
An IOAM-Domain is defined by its perimeter or edge. The operator of
an IOAM-Domain is expected to put provisions in place to ensure that
packets that contain IOAM data fields do not leak beyond the edge of
an IOAM-Domain, e.g., using packet filtering methods. The operator
should consider the potential operational impact of IOAM on
mechanisms such as ECMP load-balancing schemes (e.g., load-balancing
schemes based on packet length could be impacted by the increased
packet size due to IOAM), path MTU (i.e., ensure that the MTU of all
links within a domain is sufficiently large enough to support the
increased packet size due to IOAM), and ICMP message handling.

An IOAM-Domain consists of "IOAM encapsulating nodes", "IOAM
decapsulating nodes", and "IOAM transit nodes". The role of a node
(i.e., encapsulating, transit, decapsulating) is defined within an
IOAM-Namespace (see below). A node can have different roles in
different IOAM-Namespaces.

An IOAM encapsulating node incorporates one or more IOAM Option-Types
into packets that IOAM is enabled for. If IOAM is enabled for a
selected subset of the traffic, the IOAM encapsulating node is
responsible for applying the IOAM functionality to the selected
subset.

An IOAM transit node updates one or more of the IOAM-Data-Fields. If
both the Pre-allocated and the Incremental Trace Option-Types are
present in the packet, each IOAM transit node will update at most one
of these Option-Types. Note that in case both Trace Option-Types are
present in a packet, it is up to the IOAM data processing systems
(see Section 6) to integrate the data from the two Trace Option-Types
to form a view of the entire journey of the packet. A transit node
does not add new IOAM Option-Types to a packet and does not change
the IOAM-Data-Fields of an IOAM Edge-to-Edge (E2E) Option-Type.

An IOAM decapsulating node removes any IOAM Option-Types from
packets.

The role of an IOAM encapsulating, IOAM transit, or IOAM
decapsulating node is always performed within a specific IOAM-
Namespace. This means that an IOAM node that is, e.g., an IOAM
decapsulating node for IOAM-Namespace "A" but not for IOAM-Namespace
"B" will only remove the IOAM Option-Types for IOAM-Namespace "A"
from the packet. An IOAM decapsulating node situated at the edge of
an IOAM-Domain removes all IOAM Option-Types and associated
encapsulation headers for all IOAM-Namespaces from the packet.

IOAM-Namespaces allow for a namespace-specific definition and
interpretation of IOAM-Data-Fields. Please refer to Section 7.1 for
a discussion of IOAM-Namespaces.

Export of Export of Export of Export of
IOAM data IOAM data IOAM data IOAM data
(optional) (optional) (optional) (optional)
^ ^ ^ ^
| | | |
| | | |
User +---+----+ +---+----+ +---+----+ +---+----+
packets |Encapsu-| | Transit| | Transit| |Decapsu-|
-------->|lating |====>| Node |====>| Node |====>|lating |-->
|Node | | A | | B | |Node |
+--------+ +--------+ +--------+ +--------+

Figure 1: Roles of IOAM Nodes

IOAM nodes that add or remove the IOAM-Data-Fields can also update
the IOAM-Data-Fields at the same time. Or, in other words, IOAM
encapsulating or decapsulating nodes can also serve as IOAM transit
nodes at the same time. Note that not every node in an IOAM-Domain
needs to be an IOAM transit node. For example, a deployment might
require that packets traverse a set of firewalls that support IOAM.
In that case, only the set of firewall nodes would be IOAM transit
nodes rather than all nodes.

4. Types of IOAM

IOAM supports different modes of operation. These modes are
differentiated by the type of IOAM data fields that are being carried
in the packet, the data being collected, the type of nodes that
collect or update data, and if and how nodes export IOAM information.

Per-hop tracing: OAM information about each IOAM node a packet
traverses is collected and stored within the user data packet as
the packet progresses through the IOAM-Domain. Potential uses of
IOAM per-hop tracing include:

* Understanding the different paths that different packets
traverse between an IOAM encapsulating node and an IOAM
decapsulating node in a network that uses load balancing, such
as Equal Cost Multi-Path (ECMP). This information could be
used to tune the algorithm for ECMP for optimized network
resource usage.

* With regard to operations and troubleshooting, understanding
which path a particular packet or set of packets take as well
as what amount of jitter and delay different IOAM nodes in the
path contribute to the overall delay and jitter between the
IOAM encapsulating node and the IOAM decapsulating node.

Proof of Transit: Information that a verifier node can use to verify
whether a packet has traversed all nodes that it is supposed to
traverse is stored within the user data packet. For example,
Proof of Transit could be used to verify that a packet indeed
passes through all services of a service function chain (e.g.,
verify whether a packet indeed traversed the set of firewalls that
it is expected to traverse) or whether a packet indeed took the
expected path.

Edge-to-Edge (E2E): OAM information that is specific to the edges of
an IOAM-Domain is collected and stored within the user data
packet. E2E OAM could be used to gather operational information
about a particular network domain, such as the delay and jitter
incurred by that network domain or the traffic matrix of the
network domain.

Direct Export: OAM information about each IOAM node a packet
traverses is collected and immediately exported to a collector.
Direct Export could be used in situations where per-hop tracing
information is desired, but gathering the information within the
packet -- as with per-hop tracing -- is not feasible. Rather than
automatically correlating the per-hop tracing information, as done
with per-hop tracing, Direct Export requires a collector to
correlate the information from the individual nodes. In addition,
all nodes enabled for Direct Export need to be capable of
exporting the IOAM information to the collector.

4.1. Per-Hop Tracing IOAM

"IOAM tracing data" is expected to be collected at every IOAM transit
node that a packet traverses to ensure visibility into the entire
path that a packet takes within an IOAM-Domain. In other words, in a
typical deployment, all nodes in an IOAM-Domain would participate in
IOAM and, thus, be IOAM transit nodes, IOAM encapsulating nodes, or
IOAM decapsulating nodes. If not all nodes within a domain are IOAM
capable, IOAM tracing information (i.e., node data, see below) will
only be collected on those nodes that are IOAM capable. Nodes that
are not IOAM capable will forward the packet without any changes to
the IOAM-Data-Fields. The maximum number of hops and the minimum
path MTU of the IOAM-Domain are assumed to be known.

IOAM offers two different Trace Option-Types: the "Incremental" Trace
Option-Type and the "Pre-allocated" Trace Option-Type. For a
discussion about which of the two option types is the most suitable
for an implementation and/or deployment, see Section 7.3.

Every node data entry holds information for a particular IOAM transit
node that is traversed by a packet. The IOAM decapsulating node
removes any IOAM Option-Types and processes and/or exports the
associated data. All IOAM-Data-Fields are defined in the context of
an IOAM-Namespace.

IOAM tracing can, for example, collect the following types of
information:

* Identification of the IOAM node. An IOAM node identifier can
match to a device identifier or a particular control point or
subsystem within a device.

* Identification of the interface that a packet was received on,
i.e., ingress interface.

* Identification of the interface that a packet was sent out on,
i.e., egress interface.

* Time of day when the packet was processed by the node as well as
the transit delay. Different definitions of processing time are
feasible and expected, though it is important that all devices of
an IOAM-Domain follow the same definition.

* Generic data, which is format-free information, where the syntax
and semantics of the information are defined by the operator in a
specific deployment. For a specific IOAM-Namespace, all IOAM
nodes should interpret the generic data the same way. Examples
for generic IOAM data include geolocation information (location of
the node at the time the packet was processed), buffer queue fill
level or cache fill level at the time the packet was processed, or
even a battery charge level.

* Information to detect whether IOAM trace data was added at every
hop or whether certain hops in the domain weren't IOAM transit
nodes.

* Data that relates to how the packet traversed a node (transit
delay, buffer occupancy in case the packet was buffered, and queue
depth in case the packet was queued).

The Incremental Trace Option-Type and Pre-allocated Trace Option-Type
are defined in [RFC9197].

4.2. Proof of Transit IOAM

The IOAM Proof of Transit Option-Type is to support path or service
function chain [RFC7665] verification use cases. Proof of transit
could use methods like nested hashing or nested encryption of the
IOAM data.

The IOAM Proof of Transit Option-Type consists of a fixed-size "IOAM
Proof of Transit Option header" and "IOAM Proof of Transit Option
data fields". For details, see [RFC9197].

4.3. E2E IOAM

The IOAM E2E Option-Type is to carry the data that is added by the
IOAM encapsulating node and interpreted by IOAM decapsulating node.
The IOAM transit nodes may process the data but must not modify it.

The IOAM E2E Option-Type consists of a fixed-size "IOAM Edge-to-Edge
Option-Type header" and "IOAM Edge-to-Edge Option-Type data fields".
For details, see [RFC9197].

4.4. Direct Export IOAM

Direct Export is an IOAM mode of operation within which IOAM data are
to be directly exported to a collector rather than be collected
within the data packets. The IOAM Direct Export Option-Type consists
of a fixed-size "IOAM direct export option header". Direct Export
for IOAM is defined in [RFC9326].

5. IOAM Encapsulations

IOAM data fields and associated data types for IOAM are defined in
[RFC9197]. The IOAM data field can be transported by a variety of
transport protocols, including NSH, Segment Routing, Geneve, BIER,
IPv6, etc.

5.1. IPv6

IOAM encapsulation for IPv6 is defined in [IOAM-IPV6-OPTIONS], which
also discusses IOAM deployment considerations for IPv6 networks.

5.2. NSH

IOAM encapsulation for NSH is defined in [IOAM-NSH].

5.3. BIER

IOAM encapsulation for BIER is defined in [BIER-IOAM].

5.4. GRE

IOAM encapsulation for GRE is outlined as part of the "EtherType
Protocol Identification of In-situ OAM Data" in [IOAM-ETH].

5.5. Geneve

IOAM encapsulation for Geneve is defined in [IOAM-GENEVE].

5.6. Segment Routing

IOAM encapsulation for Segment Routing is defined in [MPLS-IOAM].

5.7. Segment Routing for IPv6

IOAM encapsulation for Segment Routing over IPv6 is defined in
[IOAM-SRV6].

5.8. VXLAN-GPE

IOAM encapsulation for VXLAN-GPE is defined in [IOAM-VXLAN-GPE].

6. IOAM Data Export

IOAM nodes collect information for packets traversing a domain that
supports IOAM. IOAM decapsulating nodes, as well as IOAM transit
nodes, can choose to retrieve IOAM information from the packet,
process the information further, and export the information using,
e.g., IP Flow Information Export (IPFIX).

Raw data export of IOAM data using IPFIX is discussed in
[IOAM-RAWEXPORT]. "Raw export of IOAM data" refers to a mode of
operation where a node exports the IOAM data as it is received in the
packet. The exporting node does not interpret, aggregate, or
reformat the IOAM data before it is exported. Raw export of IOAM
data is to support an operational model where the processing and
interpretation of IOAM data is decoupled from the operation of
encapsulating/updating/decapsulating IOAM data, which is also
referred to as "IOAM data-plane operation". Figure 2 shows the
separation of concerns for IOAM export. Exporting IOAM data is
performed by the "IOAM node", which performs IOAM data-plane
operation, whereas the interpretation of IOAM data is performed by
one or several IOAM data processing systems. The separation of
concerns is to offload interpretation, aggregation, and formatting of
IOAM data from the node that performs data-plane operations. In
other words, a node that is focused on data-plane operations, i.e.,
forwarding of packets and handling IOAM data, will not be tasked to
also interpret the IOAM data. Instead, that node can leave this task
to another system or a set of systems. For scalability reasons, a
single IOAM node could choose to export IOAM data to several systems
that process IOAM data. Similarly, several monitoring systems or
analytics systems can be used to further process the data received
from the IOAM preprocessing systems. Figure 2 shows an overview of
IOAM export, including IOAM data processing systems and monitoring
and analytics systems.

+--------------+
+-------------+ |
| Monitoring/ | |
| Analytics | |
| system(s) |-+
+-------------+
^
| Processed/interpreted/
| aggregated IOAM data
|
+--------------+
+-------------+ |
| IOAM data | |
| processing | |
| system(s) |-+
+-------------+
^
| Raw export of
| IOAM data
|
+--------------+-------+------+--------------+
| | | |
| | | |
User +---+----+ +---+----+ +---+----+ +---+----+
packets |Encapsu-| | Transit| | Transit| |Decapsu-|
-------->|lating |====>| Node |====>| Node |====>|lating |-->
|Node | | A | | B | |Node |
+--------+ +--------+ +--------+ +--------+

Figure 2: IOAM Framework with Data Export

7. IOAM Deployment Considerations

This section describes several concepts of IOAM and provides
considerations that need to be taken into account when implementing
IOAM in a network domain. This includes concepts like IOAM-
Namespaces, IOAM Layering, traffic-sets that IOAM is applied to, and
IOAM Loopback. For a definition of IOAM-Namespaces and IOAM
Layering, please refer to [RFC9197]. IOAM Loopback is defined in
[RFC9322].

7.1. IOAM-Namespaces

IOAM-Namespaces add further context to IOAM Option-Types and
associated IOAM-Data-Fields. IOAM-Namespaces are defined in
Section 4.3 of [RFC9197]. The Namespace-ID is part of the IOAM
Option-Type definition. See Section 4.4 of [RFC9197] for IOAM Trace
Option-Types or Section 4.6 of [RFC9197] for the IOAM E2E Option-
Type. IOAM-Namespaces support several uses:

* IOAM-Namespaces can be used by an operator to distinguish between
different operational domains. Devices at domain edges can filter
on Namespace-IDs to provide for proper IOAM-Domain isolation.

* IOAM-Namespaces provide additional context for IOAM-Data-Fields;
thus, they ensure that IOAM-Data-Fields are unique and can be
interpreted properly by management stations or network
controllers. While, for example, the node identifier field does
not need to be unique in a deployment (e.g., an operator may wish
to use different node identifiers for different IOAM layers, even
within the same device; or node identifiers might not be unique
for other organizational reasons, such as after a merger of two
formerly separated organizations), the combination of node_id and
Namespace-ID should always be unique. Similarly, IOAM-Namespaces
can be used to define how certain IOAM-Data-Fields are
interpreted. IOAM offers three different timestamp format
options. The Namespace-ID can be used to determine the timestamp
format. IOAM-Data-Fields (e.g., buffer occupancy) that do not
have a unit associated are to be interpreted within the context of
an IOAM-Namespace. The Namespace-ID could also be used to
distinguish between different types of interfaces. An interface-
id could, for example, point to a physical interface (e.g., to
understand which physical interface of an aggregated link is used
when receiving or transmitting a packet). Whereas, in another
case, an interface-id could refer to a logical interface (e.g., in
case of tunnels). Namespace-IDs could be used to distinguish
between the different types of interfaces.

* IOAM-Namespaces can be used to identify different sets of devices
(e.g., different types of devices) in a deployment. If an
operator desires to insert different IOAM-Data-Fields based on the
device, the devices could be grouped into multiple IOAM-
Namespaces. This could be due to the fact that the IOAM feature
set differs between different sets of devices, or it could be for
reasons of optimized space usage in the packet header. It could
also stem from hardware or operational limitations on the size of
the trace data that can be added and processed, preventing
collection of a full trace for a flow.

- Assigning different IOAM Namespace-IDs to different sets of
nodes or network partitions and using the Namespace-ID as a
selector at the IOAM encapsulating node, a full trace for a
flow could be collected and constructed via partial traces in
different packets of the same flow. For example, an operator
could choose to group the devices of a domain into two IOAM-
Namespaces in a way that, on average, only every second hop
would be recorded by any device. To retrieve a full view of
the deployment, the captured IOAM-Data-Fields of the two IOAM-
Namespaces need to be correlated.

- Assigning different IOAM Namespace-IDs to different sets of
nodes or network partitions and using a separate instance of an
IOAM Option-Type for each Namespace-ID, a full trace for a flow
could be collected and constructed via partial traces from each
IOAM Option-Type in each of the packets in the flow. For
example, an operator could choose to group the devices of a
domain into two IOAM-Namespaces in a way that each IOAM-
Namespace is represented by one of two IOAM Option-Types in the
packet. Each node would record data only for the IOAM-
Namespace that it belongs to, ignoring the other IOAM Option-
Type with an IOAM-Namespace it doesn't belong to. To retrieve
a full view of the deployment, the captured IOAM-Data-Fields of
the two IOAM-Namespaces need to be correlated.

7.2. IOAM Layering

If several encapsulation protocols (e.g., in case of tunneling) are
stacked on top of each other, IOAM-Data-Fields could be present in
different protocol fields at different layers. Layering allows
operators to instrument the protocol layer they want to measure. The
behavior follows the ships-in-the-night model, i.e., IOAM-Data-Fields
in one layer are independent of IOAM-Data-Fields in another layer.
Or in other words, even though the term "layering" often implies
there is some form of hierarchy and relationship, in IOAM, layers are
independent of each other and don't assume any relationship among
them. The different layers could, but do not have to, share the same
IOAM encapsulation mechanisms. Similarly, the semantics of the IOAM-
Data-Fields can, but do not have to, be associated to cross different
layers. For example, a node that inserts node-id information into
two different layers could use "node-id=10" for one layer and "node-
id=1000" for the second layer.

Figure 3 shows an example of IOAM Layering. The figure shows a
Geneve tunnel carried over IPv6, which starts at node A and ends at
node D. IOAM information is encapsulated in IPv6 as well as in
Geneve. At the IPv6 layer, node A is the IOAM encapsulating node
(into IPv6), node D is the IOAM decapsulating node, and nodes B and C
are IOAM transit nodes. At the Geneve layer, node A is the IOAM
encapsulating node (into Geneve), and node D is the IOAM
decapsulating node (from Geneve). The use of IOAM at both layers, as
shown in the example here, could be used to reveal which nodes of an
underlay (here the IPv6 network) are traversed by a tunneled packet
in an overlay (here the Geneve network) -- which assumes that the
IOAM information encapsulated by nodes A and D into Geneve and IPv6
is associated to each other.

+---+----+ +---+----+
User |Geneve | |Geneve |
packets |Encapsu-| |Decapsu-|
-------->|lating |==================================>|lating |-->
| Node | | Node |
| A | | D |
+--------+ +--------+
^ ^
| |
v v
+--------+ +--------+ +--------+ +--------+
|IPv6 | | IPv6 | | IPv6 | |IPv6 |
|Encapsu-| | Transit| | Transit| |Decapsu-|
|lating |====>| Node |====>| Node |====>|lating |
| Node | | | | | | Node |
| A | | B | | C | | D |
+--------+ +--------+ +--------+ +--------+

Figure 3: IOAM Layering Example

7.3. IOAM Trace Option-Types

IOAM offers two different IOAM Option-Types for tracing:
"Incremental" Trace Option-Type and "Pre-allocated" Trace Option-
Type. "Incremental" refers to a mode of operation where the packet
is expanded at every IOAM node that adds IOAM-Data-Fields. "Pre-
allocated" describes a mode of operation where the IOAM encapsulating
node allocates room for all IOAM-Data-Fields in the entire IOAM-
Domain. More specifically:

Pre-allocated Trace Option: This trace option is defined as a
container of node data fields with pre-allocated space for each
node to populate its information. This option is useful for
implementations where it is efficient to allocate the space once
and index into the array to populate the data during transit
(e.g., software forwarders often fall into this class).

Incremental Trace Option: This trace option is defined as a
container of node data fields where each node allocates and pushes
its node data immediately following the option header.

Which IOAM Trace Option-Types can be supported is not only a function
of operator-defined configuration but may also be limited by protocol
constraints unique to a given encapsulating protocol. For
encapsulating protocols that support both IOAM Trace Option-Types,
the operator decides, by means of configuration, which Trace Option-
Type(s) will be used for a particular domain. In this case,
deployments can mix devices that include either the Incremental Trace
Option-Type or the Pre-allocated Trace Option-Type. For example, if
different types of packet forwarders and associated different types
of IOAM implementations exist in a deployment and the encapsulating
protocol supports both IOAM Trace Option-Types, a deployment can mix
devices that include either the Incremental Trace Option-Type or the
Pre-allocated Trace Option-Type. As a result, both Option-Types can
be present in a packet. IOAM decapsulating nodes remove both types
of Trace Option-Types from the packet.

The two different Option-Types cater to different packet-forwarding
infrastructures and allow an optimized implementation of IOAM
tracing:

Pre-allocated Trace Option: For some implementations of packet
forwarders, it is efficient to allocate the space for the maximum
number of nodes that IOAM Trace Data-Fields should be collected
from and insert/update information in the packet at flexible
locations based on a pointer retrieved from a field in the packet.
The IOAM encapsulating node allocates an array of the size of the
maximum number of nodes that IOAM Trace Data-Fields should be
collected from. IOAM transit nodes index into the array to
populate the data during transit. Software forwarders often fall
into this class of packet-forwarder implementations. The maximum
number of nodes that IOAM information could be collected from is
configured by the operator on the IOAM encapsulating node. The
operator has to ensure that the packet with the pre-allocated
array that carries the IOAM Data-Fields does not exceed the MTU of
any of the links in the IOAM-Domain.

Incremental Trace Option: Looking up a pointer contained in the
packet and inserting/updating information at a flexible location
in the packet as a result of the pointer lookup is costly for some
forwarding infrastructures. Hardware-based packet-forwarding
infrastructures often fall into this category. Consequently,
hardware-based packet forwarders could choose to support the IOAM
Incremental Trace Option-Type. The IOAM Incremental Trace Option-
Type eliminates the need for the IOAM transit nodes to read the
full array in the Trace Option-Type and allows packets to grow to
the size of the MTU of the IOAM-Domain. IOAM transit nodes will
expand the packet and insert the IOAM-Data-Fields as long as there
is space available in the packet, i.e., as long as the size of the
packet stays within the bounds of the MTU of the links in the
IOAM-Domain. There is no need for the operator to configure the
IOAM encapsulation node with the maximum number of nodes that IOAM
information could be collected from. The operator has to ensure
that the minimum MTU of the links in the IOAM-Domain is known to
all IOAM transit nodes.

7.4. Traffic-Sets That IOAM Is Applied To

IOAM can be deployed on all or only on subsets of the live user
traffic, e.g., per interface, based on an access control list or flow
specification defining a specific set of traffic, etc.

7.5. Loopback Flag

IOAM Loopback is used to trigger each transit device along the path
of a packet to send a copy of the data packet back to the source.
Loopback allows an IOAM encapsulating node to trace the path to a
given destination and to receive per-hop data about both the forward
and the return path. Loopback is enabled by the encapsulating node
setting the Loopback flag. Looped-back packets use the source
address of the original packet as a destination address and the
address of the node that performs the Loopback operation as source
address. Nodes that loop back a packet clear the Loopback flag
before sending the copy back towards the source. Loopack applies to
IOAM deployments where the encapsulating node is either a host or the
start of a tunnel. For details on IOAM Loopback, please refer to
[RFC9322].

7.6. Active Flag

The Active flag indicates that a packet is an active OAM packet as
opposed to regular user data traffic. Active flag is expected to be
used for active measurement using IOAM. For details on the Active
flag, please refer to [RFC9322].

Example use cases for the Active flag include:

Endpoint detailed active measurement: Synthetic probe packets are
sent between the source and destination. These probe packets
include a Trace Option-Type (i.e., either incremental or pre-
allocated). Since the probe packets are sent between the
endpoints, these packets are treated as data packets by the IOAM-
Domain and do not require special treatment at the IOAM layer.
The source, which is also the IOAM encapsulating node, can choose
to set the Active flag, providing an explicit indication that
these probe packets are meant for telemetry collection.

IOAM active measurement using probe packets: Probe packets are
generated and transmitted by an IOAM encapsulating node towards a
destination that is also the IOAM decapsulating node. Probe
packets include a Trace Option-Type (i.e., either incremental or
pre-allocated) that has its Active flag set.

IOAM active measurement using replicated data packets: Probe packets
are created by an IOAM encapsulating node by selecting some or all
of the en route data packets and replicating them. A selected
data packet that is replicated and its (possibly truncated) copy
are forwarded with one or more IOAM options, while the original
packet is forwarded, normally, without IOAM options. To the
extent possible, the original data packet and its replica are
forwarded through the same path. The replica includes a Trace
Option-Type that has its Active flag set, indicating that the IOAM
decapsulating node should terminate it. In this case, the IOAM
Active flag ensures that the replicated traffic is not forwarded
beyond the IOAM-Domain.

7.7. Brown Field Deployments: IOAM-Unaware Nodes

A network can consist of a mix of IOAM-aware and IOAM-unaware nodes.
The encapsulation of IOAM-Data-Fields into different protocols (see
also Section 5) are defined such that data packets that include IOAM-
Data-Fields do not get dropped by IOAM-unaware nodes. For example,
packets that contain the IOAM Trace Option-Types in IPv6 Hop-by-Hop
extension headers are defined with bits to indicate "00 - skip over
this option and continue processing the header". This will ensure
that when an IOAM-unaware node receives a packet with IOAM-Data-
Fields included, it does not drop the packet.

Deployments that leverage the IOAM Trace Option-Type(s) could benefit
from the ability to detect the presence of IOAM-unaware nodes, i.e.,
nodes that forward the packet but do not update or add IOAM-Data-
Fields in IOAM Trace Option-Types. The node data that is defined as
part of the IOAM Trace Option-Type(s) includes a Hop_Lim field
associated to the node identifier to detect missed nodes, i.e.,
"holes" in the trace. Monitoring/Analytics systems could utilize
this information to account for the presence of IOAM-unaware nodes in
the network.

8. IOAM Manageability

The YANG model for configuring IOAM in network nodes that support
IOAM is defined in [IOAM-YANG].

A deployment can leverage IOAM profiles to limit the scope of IOAM
features, allowing simpler implementation, verification, and
interoperability testing in the context of specific use cases that do
not require the full functionality of IOAM. An IOAM profile defines
a use case or a set of use cases for IOAM and an associated set of
rules that restrict the scope and features of the IOAM specification,
thereby limiting it to a subset of the full functionality. IOAM
profiles are defined in [IOAM-PROFILES].

For deployments where the IOAM capabilities of a node are unknown,
[RFC9359] could be used to discover the enabled IOAM capabilities of
nodes.

9. IANA Considerations

This document has no IANA actions.

10. Security Considerations

As discussed in [RFC7276], a successful attack on an OAM protocol in
general and, specifically, on IOAM can prevent the detection of
failures or anomalies or can create a false illusion of nonexistent
ones.

The Proof of Transit Option-Type (Section 4.2) is used for verifying
the path of data packets. The security considerations of POT are
further discussed in [PROOF-OF-TRANSIT].

Security considerations related to the use of IOAM flags,
particularly the Loopback flag, are found in [RFC9322].

IOAM data can be subject to eavesdropping. Although the
confidentiality of the user data is not at risk in this context, the
IOAM data elements can be used for network reconnaissance, allowing
attackers to collect information about network paths, performance,
queue states, buffer occupancy, and other information. Recon is an
improbable security threat in an IOAM deployment that is within a
confined physical domain. However, in deployments that are not
confined to a single LAN but span multiple interconnected sites (for
example, using an overlay network), the inter-site links are expected
to be secured (e.g., by IPsec) in order to avoid external
eavesdropping and introduction of malicious or false data. Another
possible mitigation approach is to use "Direct Exporting" [RFC9326].
In this case, the IOAM-related trace information would not be
available in the customer data packets but would trigger the
exporting of (secured) packet-related IOAM information at every node.
IOAM data export and securing IOAM data export is outside the scope
of this document.

IOAM can be used as a means for implementing or amplifying Denial-of-
Service (DoS) attacks. For example, a malicious attacker can add an
IOAM header to packets or modify an IOAM header in en route packets
in order to consume the resources of network devices that take part
in IOAM or collectors that analyze the IOAM data. Another example is
a packet-length attack, in which an attacker pushes headers
associated with IOAM Option-Types into data packets, causing these
packets to be increased beyond the MTU size, resulting in
fragmentation or in packet drops. Such DoS attacks can be mitigated
by deploying IOAM in confined administrative domains and by limiting
the rate and/or the percentage of packets that an IOAM encapsulating
node adds IOAM information to as well as limiting rate and/or
percentage of packets that an IOAM transit or an IOAM decapsulating
node creates to export IOAM information extracted from the data
packets that carry IOAM information.

Even though IOAM focused on limited domains [RFC8799], there might be
deployments for which it is important for IOAM transit nodes and IOAM
decapsulating nodes to know that the data received haven't been
tampered with. In those cases, the IOAM data should be integrity
protected. Integrity protection of IOAM data fields is described in
[IOAM-DATA-INTEGRITY]. In addition, since IOAM options may include
timestamps, if network devices use synchronization protocols, then
any attack on the time protocol [RFC7384] can compromise the
integrity of the timestamp-related data fields. Synchronization
attacks can be mitigated by combining a secured time distribution
scheme, e.g., [RFC8915], and by using redundant clock sources
[RFC5905] and/or redundant network paths for the time distribution
protocol [RFC8039].

At the management plane, attacks may be implemented by misconfiguring
or by maliciously configuring IOAM-enabled nodes in a way that
enables other attacks. Thus, IOAM configuration should be secured in
a way that authenticates authorized users and verifies the integrity
of configuration procedures.

Notably, IOAM is expected to be deployed in limited network domains
[RFC8799], thus, confining the potential attack vectors within the
limited domain. Indeed, in order to limit the scope of threats
within the current network domain, the network operator is expected
to enforce policies that prevent IOAM traffic from leaking outside
the IOAM-Domain and prevent an attacker from introducing malicious or
false IOAM data to be processed and used within the IOAM-Domain.
IOAM data leakage could lead to privacy issues. Consider an IOAM
encapsulating node that is a home gateway in an operator's network.
A home gateway is often identified with an individual. Revealing
IOAM data, such as "IOAM node identifier" or geolocation information
outside of the limited domain, could be harmful for that user. Note
that Direct Exporting [RFC9326] can mitigate the potential threat of
IOAM data leaking through data packets.

11. Informative References

[BIER-IOAM]
Min, X., Zhang, Z., Liu, Y., Nainar, N., and C. Pignataro,
"BIER Encapsulation for IOAM Data", Work in Progress,
Internet-Draft, draft-xzlnp-bier-ioam-05, 27 January 2023,
<https://datatracker.ietf.org/doc/html/draft-xzlnp-bier-
ioam-05>.

[IOAM-DATA-INTEGRITY]
Brockners, F., Bhandari, S., Mizrahi, T., and J. Iurman,
"Integrity of In-situ OAM Data Fields", Work in Progress,
Internet-Draft, draft-ietf-ippm-ioam-data-integrity-03, 24
November 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-ippm-ioam-data-integrity-03>.

[IOAM-ETH] Weis, B., Ed., Brockners, F., Ed., Hill, C., Bhandari, S.,
Govindan, V., Pignataro, C., Ed., Nainar, N., Ed.,
Gredler, H., Leddy, J., Youell, S., Mizrahi, T., Kfir, A.,
Gafni, B., Lapukhov, P., and M. Spiegel, "EtherType
Protocol Identification of In-situ OAM Data", Work in
Progress, Internet-Draft, draft-weis-ippm-ioam-eth-05, 21
February 2022, <https://datatracker.ietf.org/doc/html/
draft-weis-ippm-ioam-eth-05>.

[IOAM-GENEVE]
Brockners, F., Ed., Bhandari, S., Govindan, V., Pignataro,
C., Ed., Nainar, N., Ed., Gredler, H., Leddy, J., Youell,
S., Mizrahi, T., Lapukhov, P., Gafni, B., Kfir, A., and M.
Spiegel, "Geneve encapsulation for In-situ OAM Data", Work
in Progress, Internet-Draft, draft-brockners-ippm-ioam-
geneve-05, 19 November 2020,
<https://datatracker.ietf.org/doc/html/draft-brockners-
ippm-ioam-geneve-05>.

[IOAM-IPV6-OPTIONS]
Bhandari, S., Ed. and F. Brockners, Ed., "In-situ OAM IPv6
Options", Work in Progress, Internet-Draft, draft-ietf-
ippm-ioam-ipv6-options-10, 28 February 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-ippm-
ioam-ipv6-options-10>.

[IOAM-NSH] Brockners, F., Ed. and S. Bhandari, Ed., "Network Service
Header (NSH) Encapsulation for In-situ OAM (IOAM) Data",
Work in Progress, Internet-Draft, draft-ietf-sfc-ioam-nsh-
11, 30 September 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-sfc-
ioam-nsh-11>.

[IOAM-PROFILES]
Mizrahi, T., Brockners, F., Bhandari, S., Ed.,
Sivakolundu, R., Pignataro, C., Kfir, A., Gafni, B.,
Spiegel, M., and T. Zhou, "In Situ OAM Profiles", Work in
Progress, Internet-Draft, draft-mizrahi-ippm-ioam-profile-
06, 17 February 2022,
<https://datatracker.ietf.org/doc/html/draft-mizrahi-ippm-
ioam-profile-06>.

[IOAM-RAWEXPORT]
Spiegel, M., Brockners, F., Bhandari, S., and R.
Sivakolundu, "In-situ OAM raw data export with IPFIX",
Work in Progress, Internet-Draft, draft-spiegel-ippm-ioam-
rawexport-06, 21 February 2022,
<https://datatracker.ietf.org/doc/html/draft-spiegel-ippm-
ioam-rawexport-06>.

[IOAM-SRV6]
Ali, Z., Gandhi, R., Filsfils, C., Brockners, F., Nainar,
N., Pignataro, C., Li, C., Chen, M., and G. Dawra,
"Segment Routing Header encapsulation for In-situ OAM
Data", Work in Progress, Internet-Draft, draft-ali-spring-
ioam-srv6-06, 10 July 2022,
<https://datatracker.ietf.org/doc/html/draft-ali-spring-
ioam-srv6-06>.

[IOAM-VXLAN-GPE]
Brockners, F., Bhandari, S., Govindan, V., Pignataro, C.,
Gredler, H., Leddy, J., Youell, S., Mizrahi, T., Kfir, A.,
Gafni, B., Lapukhov, P., and M. Spiegel, "VXLAN-GPE
Encapsulation for In-situ OAM Data", Work in Progress,
Internet-Draft, draft-brockners-ipxpm-ioam-vxlan-gpe-03, 4
November 2019, <https://datatracker.ietf.org/doc/html/
draft-brockners-ippm-ioam-vxlan-gpe-03>.

[IOAM-YANG]
Zhou, T., Ed., Guichard, J., Brockners, F., and S.
Raghavan, "A YANG Data Model for In-Situ OAM", Work in
Progress, Internet-Draft, draft-ietf-ippm-ioam-yang-06, 27
February 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-ippm-ioam-yang-06>.

[MPLS-IOAM]
Gandhi, R., Ed., Brockners, F., Wen, B., Decraene, B., and
H. Song, "MPLS Data Plane Encapsulation for In Situ OAM
Data", Work in Progress, Internet-Draft, draft-gandhi-
mpls-ioam-10, 10 March 2023,
<https://datatracker.ietf.org/doc/html/draft-gandhi-mpls-
ioam-10>.

[PROOF-OF-TRANSIT]
Brockners, F., Ed., Bhandari, S., Ed., Mizrahi, T., Ed.,
Dara, S., and S. Youell, "Proof of Transit", Work in
Progress, Internet-Draft, draft-ietf-sfc-proof-of-transit-
08, 31 October 2020,
<https://datatracker.ietf.org/doc/html/draft-ietf-sfc-
proof-of-transit-08>.

[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
DOI 10.17487/RFC2784, March 2000,
<https://www.rfc-editor.org/info/rfc2784>.

[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.

[RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
Weingarten, "An Overview of Operations, Administration,
and Maintenance (OAM) Tools", RFC 7276,
DOI 10.17487/RFC7276, June 2014,
<https://www.rfc-editor.org/info/rfc7276>.

[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in
Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
October 2014, <https://www.rfc-editor.org/info/rfc7384>.

[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>.

[RFC8039] Shpiner, A., Tse, R., Schelp, C., and T. Mizrahi,
"Multipath Time Synchronization", RFC 8039,
DOI 10.17487/RFC8039, December 2016,
<https://www.rfc-editor.org/info/rfc8039>.

[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.

[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>.

[RFC8799] Carpenter, B. and B. Liu, "Limited Domains and Internet
Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
<https://www.rfc-editor.org/info/rfc8799>.

[RFC8915] Franke, D., Sibold, D., Teichel, K., Dansarie, M., and R.
Sundblad, "Network Time Security for the Network Time
Protocol", RFC 8915, DOI 10.17487/RFC8915, September 2020,
<https://www.rfc-editor.org/info/rfc8915>.

[RFC8926] Gross, J., Ed., Ganga, I., Ed., and T. Sridhar, Ed.,
"Geneve: Generic Network Virtualization Encapsulation",
RFC 8926, DOI 10.17487/RFC8926, November 2020,
<https://www.rfc-editor.org/info/rfc8926>.

[RFC9197] Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,
Ed., "Data Fields for In Situ Operations, Administration,
and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,
May 2022, <https://www.rfc-editor.org/info/rfc9197>.

[RFC9322] Mizrahi, T., Brockners, F., Bhandari, S., Gafni, B., and
M. Spiegel, "In Situ Operations, Administration, and
Maintenance (IOAM) Loopback and Active Flags", RFC 9322,
DOI 10.17487/RFC9322, November 2022,
<https://www.rfc-editor.org/info/rfc9322>.

[RFC9326] Song, H., Gafni, B., Brockners, F., Bhandari, S., and T.
Mizrahi, "In Situ Operations, Administration, and
Maintenance (IOAM) Direct Exporting", RFC 9326,
DOI 10.17487/RFC9326, November 2022,
<https://www.rfc-editor.org/info/rfc9326>.

[RFC9359] Min, X., Mirsky, G., and L. Bo, "Echo Request/Reply for
Enabled In Situ OAM (IOAM) Capabilities", RFC 9359,
DOI 10.17487/RFC9359, April 2023,
<https://www.rfc-editor.org/info/rfc9359>.

[VXLAN-GPE]
Maino, F., Ed., Kreeger, L., Ed., and U. Elzur, Ed.,
"Generic Protocol Extension for VXLAN (VXLAN-GPE)", Work
in Progress, Internet-Draft, draft-ietf-nvo3-vxlan-gpe-12,
22 September 2021, <https://datatracker.ietf.org/doc/html/
draft-ietf-nvo3-vxlan-gpe-12>.

Acknowledgements

The authors would like to thank Tal Mizrahi, Eric Vyncke, Nalini
Elkins, Srihari Raghavan, Ranganathan T S, Barak Gafni, Karthik Babu
Harichandra Babu, Akshaya Nadahalli, LJ Wobker, Erik Nordmark,
Vengada Prasad Govindan, Andrew Yourtchenko, Aviv Kfir, Tianran Zhou,
Zhenbin (Robin), Joe Clarke, Al Morton, Tom Herbet, Haoyu Song, and
Mickey Spiegel for the comments and advice on IOAM.

Authors' Addresses

Frank Brockners (editor)
Cisco Systems, Inc.
Hansaallee 249, 3rd Floor
40549 DUESSELDORF
Germany
Email: [email protected]

Shwetha Bhandari (editor)
Thoughtspot
3rd Floor, Indiqube Orion
Garden Layout, HSR Layout
24th Main Rd
Bangalore 560 102
KARNATAKA
India
Email: [email protected]

Daniel Bernier
Bell Canada
Canada
Email: [email protected]

Tal Mizrahi (editor)
Huawei
8-2 Matam
Haifa 3190501
Israel
Email: [email protected]