Internet-Draft ICMP Node ID July 2024
Fenner & Thomas Expires 6 January 2025 [Page]
Internet Area Working Group
Intended Status:
Standards Track
B. Fenner
Arista Networks
R. Thomas
Arista Networks

Extending ICMP for Node Identification


RFC5837 describes a mechanism for Extending ICMP for Interface and Next-Hop Identification, which allows providing additional information in an ICMP error that helps identify interfaces participating in the path. This is especially useful in environments where each interface may not have a unique IP address to respond to, e.g., a traceroute.

This document introduces a similar ICMP extension for Node Identification. It allows providing a unique IP address and/or a textual name for the node, in the case where each node may not have a unique IP address (e.g., the IPv6 nexthop deployment case described in draft-chroboczek-intarea-v4-via-v6).

About This Document

This note is to be removed before publishing as an RFC.

The latest revision of this draft can be found at Status information for this document may be found at

Discussion of this document takes place on the Internet Area Working Group Working Group mailing list (, which is archived at Subscribe at

Source for this draft and an issue tracker can be found at

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

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 6 January 2025.

Table of Contents

1. Introduction

In addition to adding incoming interface information to a traceroute using the mechanisms described in [RFC5837], a network operator may be interested in adding information to identify nodes themselves. [I-D.chroboczek-intarea-v4-via-v6] describes a scenario in which individual nodes do not have unique IPv4 addresses to use to reply to an IPv4 traceroute, so additional information is needed.

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.

3. Node Identification Object

This section defines the Node Identification Object, an ICMP Extension Object with a Class-Num (Object Class Value) of 5 that can be appended to the following messages:

For reasons described in [RFC4884], this extension cannot be appended to any of the currently defined ICMPv4 or ICMPv6 messages other than those listed above.

The extension defined herein MAY be appended to any of the above listed messages and SHOULD be appended whenever required to identify the node and when local policy or security considerations do not supersede this requirement.

Similarly to the Interface Identification Object defined in [RFC5837], there are two different pieces of information that can appear in a Node Information Object.

  1. An IP Address Sub-Object MAY be included, containing an address of sufficient scope to identify the node within the domain. The IP Address Sub-Object is defined in Section 3.2 of this memo.

  2. A Node Name Sub-Object MAY be included, as specified in Section 3.3, containing up to 63 octets of the yang sys:hostname or another appropriate name uniquely identifying the node.

3.1. C-Type Meaning in a Node Identification Object

The C-Type contains a bitmask describing what information is included in this Node Identification Object.

Bit     0       1       2       3       4       5       6       7
    |               Reserved                | IPAddr|  name | Rsvd2 |
Figure 1: C-Type for the Node Identification Object

The following are bit-field definitions for C-Type:

Reserved (bits 0-4): These bits are reserved for future use and MUST be set to 0 on transmit and ignored on receipt.

IP Addr (bit 5) : When set, a Node IP Address Sub-Object is present. When clear, an IP Address Sub-Object is not present. The Node IP Address Sub-Object is described in Section 3.2 of this memo.

Node Name (bit 6): When set, a Node Name Sub-Object is included. When clear, it is not included. The Node Name Sub-Object is described in Section 3.3 of this memo.

Rsvd2 (bit 7): This bit is reserved for future use and MUST be set to 0 on transmit and ignored on receipt.

The information included does not self-identify, so this specification defines a specific ordering for sending the information that must be followed.

If bit 5 (IP Address) is set, a Node IP Address Sub-Object MUST be sent first. If bit 6 (Name) is set, a Node Name Sub-Object MUST be sent next. The information order is thus: IP Address Sub-Object, Node Name Sub-Object. Any or all pieces of information may be present or absent, as indicated by the C-Type. Any data that follows these optional pieces of information MUST be ignored.

It is valid (though pointless until additional bits are assigned by IANA) to receive a Node Information Object where bits 5 and 6 are both 0; this MUST NOT generate a warning or error.

3.2. Node IP Address Sub-Object

If the Node Identification Object identifies the node by address, the Object Payload contains an address sufficient to identify the node within the appropriate scope - global or as otherwise configured - as depicted in Figure 2.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
|              AFI              |            Reserved           |
|                           Address...
Figure 2: Node Identification Object - C-Type 2 Payload

Payload fields are defined as follows:

  • Address Family Identifier (AFI): This 16-bit field identifies the type of address represented by the Address field. Values for this field represent a subset of values found in the IANA registry of Address Family Numbers (available from [IANA.address-family-numbers]). Valid values are 1 (representing a 32-bit IPv4 address) and 2 (representing a 128-bit IPv6 address).

  • Reserved: This field MUST be set to 0 and ignored upon receipt.

  • Address: This variable-length field represents an address of appropriate scope (global, if none other defined) that can be used to identify the node.

3.3. Node Name Sub-Object

Figure 3 depicts the Node Name Sub-Object:

 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    |                  Node Name...
Figure 3: Node Identification Object Node Name Sub-Object

The Node Name Sub-Object MUST have a length that is a multiple of 4 octets and MUST NOT exceed 64 octets.

The Length field represents the length of the Node Name Sub- Object, including the length and the node name in octets. The maximum valid length is 64 octets. The length is constrained to ensure there is space for the start of the original packet and additional information.

The second field contains the human-readable node name. The node name SHOULD be the sys:hostname [RFC7317], if less than 64 octets, or the first 63 octets of the sys:hostname, if the sys:hostname is longer. The node name MAY be some other human-meaningful name of the node. The node name MUST be padded with ASCII NUL characters if the object would not otherwise terminate on a 4-octet boundary.

The node name MUST be represented in the UTF-8 charset [RFC3629] using the Default Language [RFC2277].

4. Security Considerations

It may not be desirable to allow this information to be sent to an arbitrary receiver. The addition of this information SHOULD be configurable, and MUST default to off. An implementation SHOULD determine what objects may be appended to a given message based on the destination IP address of the ICMP message that will contain the objects.

The intended field of use for the extensions defined in this document is administrative debugging and troubleshooting. The extensions herein defined supply additional information in ICMP responses. These mechanisms are not intended to be used in non-debugging applications.

This document does not specify an authentication mechanism for the extension that it defines. Application developers should be aware that ICMP messages and their contents are easily spoofed.

5. IANA Considerations

This IANA has allocated the ICMP Extension Object Class value 5 to the extension described above. The corresponding Class Sub-types Registry is as follows:

Table 1
C-Type (Value) Description Reference
0-4 Unallocated - allocatable with Standards Action [This document]
5 IP Address Sub-object included [This document]
6 Name Sub-object included [This document]
7 Unallocated - allocatable with Standards Action [This document]

6. References

6.1. Normative References

IANA, "Address Family Numbers", <>.
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Alvestrand, H., "IETF Policy on Character Sets and Languages", BCP 18, RFC 2277, DOI 10.17487/RFC2277, , <>.
Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, , <>.
Bonica, R., Gan, D., Tappan, D., and C. Pignataro, "Extended ICMP to Support Multi-Part Messages", RFC 4884, DOI 10.17487/RFC4884, , <>.
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, , <>.
Bierman, A. and M. Bjorklund, "A YANG Data Model for System Management", RFC 7317, DOI 10.17487/RFC7317, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.

6.2. Informative References

Chroboczek, J., Kumari, W. A., and T. Høiland-Jørgensen, "IPv4 routes with an IPv6 next hop", Work in Progress, Internet-Draft, draft-chroboczek-intarea-v4-via-v6-00, , <>.

Appendix A. Change history

This section is to be removed before publishing as an RFC.

A.1. Changes since draft-fenner-intarea-extended-icmp-hostid-00

  • Instead of having two different messages with the same Class Value and different CType values, we copy the bitmap implementation from [RFC5837]. The re-use of bit positions means that packet parsing and generation code can be largely reused from existing [RFC5837] code.

A.2. Changes since draft-fenner-intarea-extended-icmp-hostid-01

  • Fixed several copy-pasta errors that still referred to interface names instead of node name.


This document derives text heavily from [RFC5837], since the underlying mechanism is identical, and only the semantics of the message differs. Thanks are therefore due to that document's authors: Alia K. Atlas, Ronald P. Bonica, Carlos Pignataro, Naiming Shen and JR. Rivers.

Authors' Addresses

Bill Fenner
Arista Networks
5453 Great America Parkway
Santa Clara, California 95054
United States of America
Reji Thomas
Arista Networks
Global Tech Park
Bangalore 560103