ICMP extension to include underlay information
draft-jags-intarea-icmp-ext-underlay-info-02
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| Authors | Jaganbabu Rajamanickam , Darren Dukes , Madhan Sankaranarayanan | ||
| Last updated | 2025-08-18 (Latest revision 2025-01-30) | ||
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draft-jags-intarea-icmp-ext-underlay-info-02
Internet Area Working Group J. Rajamanickam, Ed.
Internet-Draft D. Dukes
Intended status: Standards Track M. Sankaranarayanan
Expires: 19 February 2026 Cisco Systems, Inc.
18 August 2025
ICMP extension to include underlay information
draft-jags-intarea-icmp-ext-underlay-info-02
Abstract
Network operators operating overlay networks require the ability to
identify hops in an underlay network when traceroute in the overlay.
This document defines an ICMP Error extension message to carry the
underlay error information to the overlay network endpoint.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 19 February 2026.
Copyright Notice
Copyright (c) 2025 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
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provided without warranty as described in the Revised BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 2
3. Underlay Information Object . . . . . . . . . . . . . . . . . 3
3.1. UIO Object Format . . . . . . . . . . . . . . . . . . . . 3
3.2. Underlay Information Object Encoding Process . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. UIO ICMP Extension Message Examples . . . . . . . . . . . 5
6.1.1. UIO carrying IPv6 information to the IPv4 source . . 5
6.1.2. UIO carrying IPv4 information to the IPv6 source . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . 7
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
The mechanism allowing ICMP messages to carry additional information
is [RFC4884]. ICMP message extensions, describing the mechanisms for
extending ICMP messages to carry additional information about the
system where the error occurred are defined in [RFC5837], [RFC8335]
and [RFC8883]. These messages are transmitted to the source node to
provide deeper insight into the error in relation to the node where
it occurred.
Network operators who administer and overlay and underlay network,
such as those with VPN segmentation within their network and an SRv6
core connecting them, find it particularly useful to have ICMP
underlay information transmitted to source nodes for the purpose of
using traceroute. This ICMP underlay information provides details
about errors and failures in the underlay network.
The underlay error information described in this document satisfy the
need of these network operators.
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.
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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
This section described the UIO object 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
UIO ICMP extension object contains the following fields:
Length: 16 bits
Length of the object, measured in octets, including UIO ICMP
extension object header and object payload
Class-Num: 8 bits
Identifies object class. In the case of UIO, a new value TBA will
be assigned from IANA "ICMP Extension Object Classes and Class
Sub-types" registry. This object could co-exist with the other
ICMP extension objects
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C-Type: 8 bits
Identifies object sub-type. This value MUST be transmitted as
zeros and ignored upon receipt.
Object-Payload: Variable Length
UIO Object payload contains one or more other ICMP Extension
Objects that are related to the underlay nodes.
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 [RFC5837]
Section 4.2.
When the UIO is encoded, the total length of the ICMP message,
including extensions, MUST NOT exceed the minimum reassembly buffer
size.
If the node decoding the ICMP extension header does not recognize the
UIO ICMP extension message, it SHOULD ignore this message and
continue processing the other messages.
3.2. Underlay Information Object Encoding Process
An underlay head-end node generates an ICMP error directed to a host
in the overlay network. The specifics of the ICMP error content are
beyond the scope of this document. The error is triggered by the
receipt of an underlay error message from an IPv4/IPv6 interface.
The encoding and processing of the underlay error are also outside
the scope of this document.
The underlay head-end appends a UIO ICMP extension object to the ICMP
error it generates to the overlay host.
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4. Security Considerations
In most of the cases the overlay and underlay networks are owned by
different operators, so it may not be advisable to permit the
transmission of the underlay information to an arbitrary recipient.
The inclusion of this information should be configurable and must
default to being disabled. An implementation should decide which
objects can be appended as part of the UIO ICMP extension message.
The extensions defined in this document are intended for use in
administrative debugging and troubleshooting. They provide
additional information in ICMP responses. These mechanisms are not
designed for use in non-debugging applications.
5. IANA Considerations
This document requests that IANA allocate a value (TBA - To Be
Assigned) for the UIO ICMP extension object class value from the
"ICMP Extension Object Classes and Class Sub-types" registry to
indicate the presence of the UIO ICMP extension class, referred to as
TBA above.
6. Appendix
6.1. UIO ICMP Extension Message Examples
This section lists the UIO example encoding format
6.1.1. 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 an UIO ICMP extension object with IPv6
interface address information as follows.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ 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.
6.1.2. 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.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ 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.
7. Normative References
[IANA.address-family-numbers]
IANA, "Address Family Numbers",
<http://www.iana.org/assignments/address-family-numbers>.
[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/rfc/rfc2119>.
[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/rfc/rfc4884>.
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[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/rfc/rfc5837>.
[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/rfc/rfc8174>.
[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/rfc/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/rfc/rfc8883>.
Acknowledgments
This document derives text heavily from [RFC4884] and [RFC5837].
Contributors
The following people have substantially contributed to this document:
Tamilselvan Murugan
Cisco Systems, Inc.
Email: tammurug@cisco.com
Dhilip Sekar
Cisco Systems, Inc.
Email: dhsekar@cisco.com
Figure 4
Authors' Addresses
Jaganbabu Rajamanickam (editor)
Cisco Systems, Inc.
Canada
Email: jrajaman@cisco.com
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Darren Dukes
Cisco Systems, Inc.
Canada
Email: ddukes@cisco.com
Madhan Sankaranarayanan
Cisco Systems, Inc.
India
Email: madsanka@cisco.com
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