ICMP extension to include underlay information
draft-jags-intarea-icmp-ext-underlay-info-04
This document is an Internet-Draft (I-D).
Anyone may submit an I-D to the IETF.
This I-D is not endorsed by the IETF and has no formal standing in the
IETF standards process.
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Jaganbabu Rajamanickam , Darren Dukes , Madhan Sankaranarayanan , Ron Bonica | ||
| Last updated | 2026-02-24 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-jags-intarea-icmp-ext-underlay-info-04
Internet Area Working Group J. Rajamanickam, Ed.
Internet-Draft D. Dukes
Intended status: Standards Track M. Sankaranarayanan, Ed.
Expires: 28 August 2026 Cisco Systems, Inc.
R. Bonica
HPE
24 February 2026
ICMP extension to include underlay information
draft-jags-intarea-icmp-ext-underlay-info-04
Abstract
Network operators managing overlay networks require visibility into
underlay network hops during traceroute operations from overlay
endpoints. This document defines an ICMP extension object, the
Underlay Information Object (UIO), which allows underlay head-end
nodes to encapsulate underlay error information within ICMP error
messages. This mechanism provides overlay operators with crucial
visibility into underlay network paths for troubleshooting.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 28 August 2026.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
Rajamanickam, et al. Expires 28 August 2026 [Page 1]
Internet-Draft ICMP Underlay Info Extension February 2026
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. ICMP Error Message Origination and UIO . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. Underlay Information Object . . . . . . . . . . . . . . . . . 5
3.1. UIO Object Format . . . . . . . . . . . . . . . . . . . . 5
3.2. Underlay Information Object Encoding Process . . . . . . 6
3.3. Content Restrictions and Filtering . . . . . . . . . . . 7
3.3.1. Permitted ICMP Message Types . . . . . . . . . . . . 7
3.3.2. Permitted Extension Objects . . . . . . . . . . . . . 8
3.3.3. Size Constraints . . . . . . . . . . . . . . . . . . 8
3.3.4. Loop and Recursion Prevention . . . . . . . . . . . . 9
3.3.5. Single Source Principle . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
4.1. Information Disclosure . . . . . . . . . . . . . . . . . 9
4.2. Privacy Considerations . . . . . . . . . . . . . . . . . 10
4.3. Message Size and Amplification . . . . . . . . . . . . . 10
4.4. Spoofing and Forgery . . . . . . . . . . . . . . . . . . 10
4.5. Intended Use . . . . . . . . . . . . . . . . . . . . . . 10
4.6. Rate Limiting . . . . . . . . . . . . . . . . . . . . . . 10
4.7. Content Filtering and Sanitization . . . . . . . . . . . 11
4.7.1. Information Disclosure Risks . . . . . . . . . . . . 11
4.7.2. Amplification and Abuse Risks . . . . . . . . . . . . 11
4.8. Operational Security . . . . . . . . . . . . . . . . . . 12
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
5.1. ICMP Extension Object Class . . . . . . . . . . . . . . . 12
5.2. C-Type Values . . . . . . . . . . . . . . . . . . . . . . 13
6. Operational Considerations . . . . . . . . . . . . . . . . . 13
6.1. Configuration . . . . . . . . . . . . . . . . . . . . . . 13
6.2. Troubleshooting Workflow . . . . . . . . . . . . . . . . 13
6.3. Multi-Vendor Interoperability . . . . . . . . . . . . . . 14
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1. Normative References . . . . . . . . . . . . . . . . . . 14
7.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Appendix . . . . . . . . . . . . . . . . . . . . . . 15
A.1. UIO ICMP Extension Message Examples . . . . . . . . . . . 15
A.1.1. UIO carrying IPv6 information to the IPv4 source . . 15
A.1.2. UIO carrying IPv4 information to the IPv6 source . . 16
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 17
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
Rajamanickam, et al. Expires 28 August 2026 [Page 2]
Internet-Draft ICMP Underlay Info Extension February 2026
1. Introduction
The mechanism for ICMP messages to carry additional information is
defined in [RFC4884]. ICMP message extensions that enable ICMP
messages to carry additional information about the system where an
error occurred are defined in [RFC5837], [RFC8335], and [RFC8883].
These extensions transmit enhanced diagnostic information to the
source node.
Network operators who manage both overlay and underlay networks, such
as those operating VPN segments connected through an SRv6 core
network, require the ability to trace paths through the underlay
infrastructure. Currently, when performing traceroute operations
from an overlay endpoint, operators lack visibility into the underlay
path and cannot identify the specific underlay node where a failure
occurred. For instance, imagine a VPN service (overlay) running over
an SRv6 network (underlay). If a packet gets dropped within the SRv6
network, the VPN operator currently has no direct way to pinpoint the
exact underlay node causing the issue.
The Underlay Information Object (UIO) defined in this document
addresses this operational requirement by enabling underlay head-end
nodes to include underlay-specific diagnostic information in ICMP
error messages sent to overlay endpoints, thereby providing crucial
visibility for troubleshooting.
1.1. ICMP Error Message Origination and UIO
The mechanism described in this document, where an underlay head-end
node encapsulates underlay error information into a new ICMP error
message destined for an overlay endpoint, deviates from existing ICMP
error message origination rules. Specifically, [RFC4443],
Section 2.4, Rule (e.1) states that "An ICMPv6 error message MUST NOT
be originated as a result of receiving the following: (e.1) An ICMPv6
error message." A similar restriction exists for ICMPv4 in [RFC792].
This document defines a specific exception to this rule for the
purpose of the Underlay Information Object (UIO). The UIO mechanism
is designed to provide critical diagnostic visibility into underlay
network failures for overlay operators, a function not adequately
served by existing ICMP mechanisms. The underlay head-end node acts
as an intermediary, translating an underlay error into a new error
message containing encapsulated UIO information for the overlay,
rather than simply forwarding the original error message. This
controlled origination of a new ICMP error message, triggered by an
underlay ICMP error message, is essential for the UIO's intended
troubleshooting workflow. Therefore, this document updates [RFC4443]
to accommodate this specific behavior.
Rajamanickam, et al. Expires 28 August 2026 [Page 3]
Internet-Draft ICMP Underlay Info Extension February 2026
However, permitting this exception introduces new challenges that
must be carefully addressed. Because UIO creates an intentional
pathway for underlay diagnostic information to cross into the overlay
domain, it raises the following concerns:
* Information Leakage: Unrestricted encapsulation could expose
underlay topology, routing state, or configuration details beyond
what is necessary for troubleshooting.
* Amplification and Abuse: Without constraints, a small probe could
trigger disproportionately large ICMP responses containing UIO,
enabling amplification attacks or reconnaissance of underlay
infrastructure.
* Recursive Error Loops: An underlay head-end node generating a new
ICMP error in response to a received ICMP error that itself
contains a UIO could create infinite error loops.
* Content Integrity: Aggregating information from multiple underlay
sources into a single UIO could produce misleading diagnostic
data.
To mitigate these risks, this document defines strict content
restrictions (Section 3.3) that constrain which ICMP message types
and extension objects may be encapsulated within a UIO, enforce
message size limits, prevent loops and recursion, and ensure each UIO
originates from a single underlay source. These restrictions are
essential to making the error origination exception safe for
deployment.
2. Conventions and Definitions
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.
This document uses the following terms:
Overlay Network: A virtual network built on top of an existing
underlying network infrastructure, often providing services like
VPNs or tunnels.
Underlay Network: The physical or logical network infrastructure
over which an overlay network operates, responsible for forwarding
packets between overlay endpoints.
Rajamanickam, et al. Expires 28 August 2026 [Page 4]
Internet-Draft ICMP Underlay Info Extension February 2026
Overlay Endpoint: A device or system that terminates an overlay
network segment and originates or receives traffic for the
overlay.
Underlay Head-End Node: The node in the underlay network responsible
for encapsulating overlay traffic and often the first point of
contact for an overlay packet entering the underlay.
3. Underlay Information Object
This section defines a new ICMP extension object called Underlay
Information Object (UIO) that is encoded as part of ICMP extension
message. A new Class-Num value TBA (To Be Assigned) is assigned to
identify the UIO. As per [RFC4884], this object MAY be appended to
one of the following ICMP messages:
* ICMPv4 Time Exceeded
* ICMPv4 Destination Unreachable
* ICMPv4 Parameter Problem
* ICMPv6 Time Exceeded
* ICMPv6 Destination Unreachable
3.1. UIO Object Format
The UIO ICMP extension object has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Class-Num=TBA | C-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Object-Payload (Other ICMP Extension Objects...) ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Underlay Information Object Format
Length (16 bits): The length of this object, measured in octets,
including the object header and object payload. The length MUST
be a multiple of 4 octets and MUST be at least 8 octets.
Class-Num (8 bits): The ICMP extension object class number that
Rajamanickam, et al. Expires 28 August 2026 [Page 5]
Internet-Draft ICMP Underlay Info Extension February 2026
identifies this as a UIO object. IANA is requested to assign a
value from the "ICMP Extension Object Classes and Class Sub-types"
registry (see Section 5).
C-Type (8 bits): The object sub-type. This document defines C-Type
value 0. Additional C-Type values may be defined in future
documents. Implementations MUST set this field to 0 and SHOULD
ignore the value upon receipt.
Object-Payload (variable length): Contains one or more ICMP
Extension Objects that provide information about underlay nodes.
The payload MUST contain at least one ICMP extension object. Each
encapsulated ICMP extension object MUST be formatted according to
[RFC4884] and the specifications for that particular object class.
This ICMP extension object acts as an envelope to carry other ICMP
extension objects related to the underlay. Primarily, the UIO ICMP
extension object is encoded in the ICMP extension message by the
underlay head-end when it receives an ICMP error message from one of
its intermediate nodes.
This UIO ICMP extension object can encapsulate one or more relevant
ICMP extension objects that are related to the underlay node. When
the underlay head-end encodes its ICMP extension object, the first
object MUST contain the ICMP extension object that carries IP address
or the hostname of the node where the initial ICMP error was
generated. The ICMP extension objects encoded within the UIO ICMP
extension objects can belong to any address family, irrespective of
the address family of the source node that decapsulates the UIO ICMP
extension objects, as opposed to what is stated in Section 4.2 of
[RFC5837].
If the node decoding the ICMP extension header does not recognize the
UIO ICMP extension object, it SHOULD ignore this object and continue
processing the other objects.
3.2. Underlay Information Object Encoding Process
When an underlay head-end node receives an ICMP error message from an
underlay node and needs to forward information about this error to an
overlay endpoint, it follows this process:
1. The underlay head-end node constructs an ICMP error message
destined for the overlay endpoint.
2. The node appends a UIO ICMP extension object to this ICMP error
message according to the procedures defined in [RFC4884].
Rajamanickam, et al. Expires 28 August 2026 [Page 6]
Internet-Draft ICMP Underlay Info Extension February 2026
3. Within the UIO object payload, the node includes one or more ICMP
extension objects that carry information about the underlay node
where the original error occurred.
4. The first ICMP extension object within the UIO payload MUST
contain addressing information (e.g., using the Interface
Information Object defined in [RFC5837]) that identifies the
underlay node that generated the original error. This ensures
that the most critical diagnostic information for pinpointing the
failure source is immediately available.
5. Additional ICMP extension objects MAY be included to provide
supplementary diagnostic information about the underlay path.
6. The encapsulated ICMP extension objects within the UIO may belong
to any address family, regardless of the address family used
between the underlay head-end and the overlay endpoint.
7. The total length of the ICMP message, including all extensions,
MUST NOT exceed 576 octets for IPv4 or 1280 octets for IPv6 (the
minimum reassembly buffer sizes defined in [RFC791] and
[RFC8200], respectively).
Implementations SHOULD provide configuration options to control which
underlay information is included in UIO objects, considering security
and privacy implications discussed in Section 4.
3.3. Content Restrictions and Filtering
The Underlay Information Object crosses administrative domain
boundaries between overlay and underlay networks. To prevent
confusion, information leakage, and potential abuse, strict
restrictions apply to the content that can be encapsulated within a
UIO.
3.3.1. Permitted ICMP Message Types
An underlay head-end node MUST only encapsulate ICMP error messages
that indicate packet forwarding failures in the underlay network.
The following ICMP message types MAY be encapsulated:
* ICMPv4 Type 11 (Time Exceeded)
* ICMPv4 Type 3 (Destination Unreachable)
* ICMPv6 Type 1 (Destination Unreachable)
Rajamanickam, et al. Expires 28 August 2026 [Page 7]
Internet-Draft ICMP Underlay Info Extension February 2026
* ICMPv6 Type 2 (Packet Too Big)
* ICMPv6 Type 3 (Time Exceeded)
Other ICMP messages MUST NOT be included under UIO envelope. The
overlay host that receives the UIO messages other than the listed
above MUST be dropped.
3.3.2. Permitted Extension Objects
The UIO object payload SHOULD contain only ICMP extension objects
that provide diagnostic information about the underlay node that
generated the original ICMP error message.
The following extension object classes are RECOMMENDED for inclusion:
* Interface Information Object (Class-Num 2) [RFC5837]
* Node Identification Object (Class-Num 5)
[I-D.ietf-intarea-extended-icmp-nodeid]
* MPLS Label Stack Object (Class-Num 1) [RFC4950]
Future IETF standards-track ICMP extension objects with diagnostic
purpose MAY be included, subject to the restrictions below.
Other ICMP extension objects MUST NOT be included under UIO envelope.
The overlay host that receives the UIO messages other than the listed
above MUST be dropped.
3.3.3. Size Constraints
The total size of an ICMP message containing a UIO object MUST NOT
exceed the minimum reassembly buffer size for the IP version being
used:
* 576 octets for IPv4 [RFC791]
* 1280 octets for IPv6 [RFC8200]
To ensure sufficient space for the ICMP header, original packet
excerpt (128 octets as per [RFC4884]), and potential additional
extension objects outside the UIO, implementations SHOULD limit the
UIO object payload to a maximum of 512 octets.
If the underlay ICMP error message contains extension objects that
would cause the UIO payload to exceed this limit, the underlay head-
end node SHOULD:
Rajamanickam, et al. Expires 28 August 2026 [Page 8]
Internet-Draft ICMP Underlay Info Extension February 2026
1. Include the most critical diagnostic information first (per
Section 3.2, the Node Identification Object SHOULD be first)
2. Truncate or omit less critical extension objects
3. NOT fragment the ICMP message
3.3.4. Loop and Recursion Prevention
An underlay head-end node MUST NOT generate an ICMP error message in
response to receiving an ICMP error message that contains a UIO
object in its extension structure.
This applies regardless of whether the underlay head-end node would
normally generate an error (e.g., due to TTL expiration, routing
failure, etc.). The packet MUST be silently discarded.
Additionally, as specified in Section 3.3.2, nested UIO objects (a
UIO containing another UIO in its payload) MUST NOT be created.
3.3.5. Single Source Principle
Each UIO object MUST contain ICMP extension objects from exactly one
underlay node (the node that generated the original ICMP error
message received by the underlay head-end).
An underlay head-end node MUST NOT aggregate ICMP extension objects
from multiple underlay nodes into a single UIO object, even if
multiple errors were encountered for related packets.
If the underlay head-end needs to communicate errors from multiple
underlay nodes, it MUST generate separate ICMP messages, each with
its own UIO object.
4. Security Considerations
The UIO extension introduces several security considerations that
implementations and operators must address:
4.1. Information Disclosure
The UIO extension reveals information about the underlay network
topology and addressing to overlay endpoints. In many deployments,
the overlay and underlay networks are operated by different
administrative entities, and underlay topology information may be
considered sensitive.
Rajamanickam, et al. Expires 28 August 2026 [Page 9]
Internet-Draft ICMP Underlay Info Extension February 2026
Implementations MUST provide configuration options to control the
generation of UIO extensions. The default configuration MUST disable
UIO generation. Operators SHOULD enable UIO only for authenticated
and authorized overlay endpoints or networks. The specific
mechanisms for such authentication and authorization are outside the
scope of this document but are crucial for secure deployment.
4.2. Privacy Considerations
Underlay information may reveal details about network architecture,
capacity, and routing that could be exploited for reconnaissance or
targeted attacks. Operators SHOULD carefully consider which underlay
information to expose through UIO extensions.
4.3. Message Size and Amplification
Including UIO extensions increases ICMP message size.
Implementations MUST enforce the message size limits specified in
Section 3.2 to prevent fragmentation issues and potential
amplification attacks.
4.4. Spoofing and Forgery
As with all ICMP messages, UIO extensions are subject to spoofing
attacks. The authenticity and integrity of UIO information cannot be
guaranteed without additional security mechanisms. Implementations
and operators SHOULD NOT use UIO information for security-critical
decisions.
4.5. Intended Use
The extensions defined in this document are intended exclusively for
administrative debugging and troubleshooting purposes. They provide
diagnostic information in ICMP responses and are not designed for use
in production protocols, automation systems, or non-debugging
applications.
4.6. Rate Limiting
Implementations SHOULD apply rate limiting to the generation of ICMP
messages containing UIO extensions to prevent resource exhaustion and
potential denial-of-service conditions.
Rajamanickam, et al. Expires 28 August 2026 [Page 10]
Internet-Draft ICMP Underlay Info Extension February 2026
4.7. Content Filtering and Sanitization
The UIO mechanism crosses administrative domain boundaries between
overlay and underlay networks. This "crossing of streams" creates
potential security and operational risks if content is not carefully
filtered.
4.7.1. Information Disclosure Risks
Including inappropriate ICMP message types or extension objects in
UIO could disclose:
* Underlay network topology beyond what is necessary for
troubleshooting
* Underlay routing information (e.g., via redirect messages)
* Underlay control plane state (e.g., via router discovery)
* Proprietary or sensitive configuration details
The content restrictions in Section 3.3 are designed to limit
information disclosure to what is necessary for diagnosing forwarding
failures. Implementations MUST enforce these restrictions as
security boundaries.
Operators SHOULD NOT enable UIO for destinations outside their
administrative control without careful consideration of what
information will be disclosed.
4.7.2. Amplification and Abuse Risks
Without content and rate restrictions, UIO could be abused for:
* Amplification attacks (small query triggers large UIO response)
* Reconnaissance of underlay infrastructure
* Resource exhaustion at underlay head-end nodes
* Information gathering about overlay-underlay relationships
The following mechanisms mitigate these risks:
* Size limits (Section 3.3.3) prevent excessive amplification
* Content restrictions (Section 3.3.1, Section 3.3.2) limit
reconnaissance value
Rajamanickam, et al. Expires 28 August 2026 [Page 11]
Internet-Draft ICMP Underlay Info Extension February 2026
* Loop prevention (Section 3.3.4) prevents recursive amplification
* Rate limiting (Section 4.6) prevents resource exhaustion
Implementations MUST enforce these protections and MUST NOT provide
configuration options that bypass them (e.g., removing size limits or
allowing nested UIO).
4.8. Operational Security
Network operators deploying UIO should:
* Start with UIO disabled and enable only for specific, authorized
overlay destinations
* Monitor UIO generation rates and investigate anomalies
* Regularly review what information is being disclosed via UIO
* Coordinate with overlay operators to understand their diagnostic
needs and security requirements
* Document the security implications of UIO in their deployment
(e.g., what underlay information is visible to overlay operators)
In multi-tenant environments, operators should carefully consider
whether underlay diagnostic information should be visible to all
tenants or restricted based on tenant relationships and SLAs.
5. IANA Considerations
5.1. ICMP Extension Object Class
IANA is requested to assign a new value from the "ICMP Extension
Object Classes and Class Sub-types" registry
(https://www.iana.org/assignments/icmp-parameters/) for the Underlay
Information Object (UIO) as follows:
+=============+=============================+============+
| Class Value | Class Name | Reference |
+=============+=============================+============+
| TBA | Underlay Information Object | [This RFC] |
+-------------+-----------------------------+------------+
Table 1
Rajamanickam, et al. Expires 28 August 2026 [Page 12]
Internet-Draft ICMP Underlay Info Extension February 2026
5.2. C-Type Values
IANA is requested to establish a new sub-registry titled "Underlay
Information Object C-Types" under the "ICMP Extension Object Classes
and Class Sub-types" registry.
Initial values for this registry are as follows:
+==============+======================+============+
| C-Type Value | Description | Reference |
+==============+======================+============+
| 0 | Reserved/Unspecified | [This RFC] |
+--------------+----------------------+------------+
| 1-246 | Unassigned | |
+--------------+----------------------+------------+
| 247-255 | Reserved for Private | [This RFC] |
| | or Experimental Use | |
+--------------+----------------------+------------+
Table 2
The registration procedure for values 1-246 is Standards Action or
IESG Approval as defined in [RFC8126].
6. Operational Considerations
6.1. Configuration
Operators SHOULD carefully configure which overlay endpoints or
networks are authorized to receive UIO information. To effectively
manage the security and operational aspects of UIO, implementations
SHOULD provide configuration options, including but not limited to:
* Enable/disable UIO generation (default: disabled)
* Whitelist of authorized overlay prefixes
* Maximum UIO object payload size
* Rate limiting parameters
6.2. Troubleshooting Workflow
The intended use case for UIO is as follows:
1. An overlay operator performs traceroute from an overlay endpoint.
2. The traceroute reveals a failure point in the path.
Rajamanickam, et al. Expires 28 August 2026 [Page 13]
Internet-Draft ICMP Underlay Info Extension February 2026
3. ICMP error messages include UIO extensions with underlay details.
4. The overlay operator uses this information to coordinate with the
underlay operator for problem resolution.
6.3. Multi-Vendor Interoperability
Implementations SHOULD be tested for interoperability, particularly
when overlay and underlay equipment are from different vendors.
7. References
7.1. Normative References
[RFC792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC792, September 1981,
<https://www.rfc-editor.org/info/rfc792>.
[RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[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>.
[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>.
[RFC4950] Bonica, R., Gan, D., Tappan, D., and C. Pignataro, "ICMP
Extensions for Multiprotocol Label Switching", RFC 4950,
DOI 10.17487/RFC4950, August 2007,
<https://www.rfc-editor.org/info/rfc4950>.
[RFC4884] Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
"Extended ICMP to Support Multi-Part Messages", RFC 4884,
DOI 10.17487/RFC4884, April 2007,
<https://www.rfc-editor.org/info/rfc4884>.
[RFC5837] Atlas, A., Ed., Bonica, R., Ed., Pignataro, C., Ed., Shen,
N., and JR. Rivers, "Extending ICMP for Interface and
Next-Hop Identification", RFC 5837, DOI 10.17487/RFC5837,
April 2010, <https://www.rfc-editor.org/info/rfc5837>.
Rajamanickam, et al. Expires 28 August 2026 [Page 14]
Internet-Draft ICMP Underlay Info Extension February 2026
[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>.
[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>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8335] Bonica, R., Thomas, R., Linkova, J., Lenart, C., and M.
Boucadair, "PROBE: A Utility for Probing Interfaces",
RFC 8335, DOI 10.17487/RFC8335, February 2018,
<https://www.rfc-editor.org/info/rfc8335>.
[RFC8883] Herbert, T., "ICMPv6 Errors for Discarding Packets Due to
Processing Limits", RFC 8883, DOI 10.17487/RFC8883,
September 2020, <https://www.rfc-editor.org/info/rfc8883>.
7.2. Informative References
[I-D.ietf-intarea-extended-icmp-nodeid]
Bonica, R., Thomas, R., Linkova, J., Lenart, C., and M.
Boucadair, "Extending ICMP for Node Identification", Work
in Progress, Internet-Draft, draft-ietf-intarea-extended-
icmp-nodeid, 2024, <https://datatracker.ietf.org/doc/
draft-ietf-intarea-extended-icmp-nodeid/>.
[IANA.address-family-numbers]
IANA, "Address Family Numbers",
<http://www.iana.org/assignments/address-family-numbers>.
Appendix A. Appendix
A.1. UIO ICMP Extension Message Examples
This section lists examples of UIO encoding.
A.1.1. UIO carrying IPv6 information to the IPv4 source
In this example, a host receives an IPv4 ICMPv4 Time Exceeded error
message in response to an ICMP Echo Request as part of the traceroute
application. It also contains a UIO ICMP extension object with IPv6
interface address information as follows.
Rajamanickam, et al. Expires 28 August 2026 [Page 15]
Internet-Draft ICMP Underlay Info Extension February 2026
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ IPv4 Header ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=11 | Code=0 | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unused | Length=32 | Unused |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Part of Original Datagram (128 bytes) ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver=2 | Unused | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length=28 | Class-Num=TBA | C-Type=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length=24 | Class-Num=2 | C-Type=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI=2 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ IPv6 Address (Original Error Device) ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: ICMPv4 packet carrying UIO ICMP extension
The traceroute application displays the IPv6 Address in the UIO to
allow an administrator to trace the underlay path of the route being
traced.
A.1.2. UIO carrying IPv4 information to the IPv6 source
In this example, a host receives an IPv6 ICMPv6 Time Exceeded error
message in response to an ICMP Echo Request as part of the traceroute
application. It contains a UIO ICMP extension object with IPv4
interface address information as follows.
Rajamanickam, et al. Expires 28 August 2026 [Page 16]
Internet-Draft ICMP Underlay Info Extension February 2026
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ IPv6 Header ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=3 | Code=0 | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length=32 | Unused |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Part of Original Datagram (128 bytes) ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver=2 | Unused | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length=16 | Class-Num=TBA | C-Type=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length=12 | Class-Num=2 | C-Type=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI=1 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address (Original Error Device) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: UIO carrying IPv4 information to the IPv6 source
The traceroute application displays the IPv4 Address in the UIO to
allow an administrator to trace the underlay path of the route being
traced.
Acknowledgments
The authors thank the contributors listed below for their substantial
input and review.
Contributors
The following individuals contributed to this document:
Tamilselvan Murugan
Cisco Systems, Inc.
Email: tammurug@cisco.com
Dhilip Sekar
Email: dhilipsekar1998@gmail.com
Rajamanickam, et al. Expires 28 August 2026 [Page 17]
Internet-Draft ICMP Underlay Info Extension February 2026
Authors' Addresses
Jaganbabu Rajamanickam (editor)
Cisco Systems, Inc.
Canada
Email: jrajaman@cisco.com
Darren Dukes
Cisco Systems, Inc.
Canada
Email: ddukes@cisco.com
Madhan Sankaranarayanan (editor)
Cisco Systems, Inc.
India
Email: madsanka@cisco.com
Ron Bonica
HPE
United States of America
Email: ronald.bonica@hpe.com
Rajamanickam, et al. Expires 28 August 2026 [Page 18]