Internet-Draft PROBE September 2024
Fenner, et al. Expires 8 March 2025 [Page]
Workgroup:
int-area
Internet-Draft:
draft-fenner-intarea-probe-clarification-02
Obsoletes:
8335 (if approved)
Updates:
4884 (if approved)
Published:
Intended Status:
Standards Track
Expires:
Authors:
B. Fenner, Ed.
Arista Networks
R. Bonica
Juniper Networks
R. Thomas
Arista Networks
J. Linkova
Google
C. Lenart
Verizon
M. Boucadair
Orange

PROBE: A Utility for Probing Interfaces

Abstract

This document describes a network diagnostic tool called PROBE. PROBE is similar to PING in that it can be used to query the status of a probed interface, but it differs from PING in that it does not require bidirectional connectivity between the probing and probed interfaces. Instead, PROBE requires bidirectional connectivity between the probing interface and a proxy interface. The proxy interface can reside on the same node as the probed interface, or it can reside on a node to which the probed interface is directly connected. This document updates RFC 4884 and obsoletes RFC 8335.

About This Document

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

The latest revision of this draft can be found at https://fenner.github.io/probe-clarification/draft-fenner-intarea-probe-clarification.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-fenner-intarea-probe-clarification/.

Discussion of this document takes place on the Internet Area Area mailing list (mailto:int-area@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/int-area/. Subscribe at https://www.ietf.org/mailman/listinfo/int-area/.

Source for this draft and an issue tracker can be found at https://github.com/fenner/probe-clarification.

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 8 March 2025.

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Table of Contents

1. Introduction

Network operators use PING [RFC2151] to test bidirectional connectivity between two interfaces. For the purposes of this document, these interfaces are called the probing and probed interfaces. PING sends an ICMP [RFC0792] [RFC4443] Echo Request message from the probing interface to the probed interface. The probing interface resides on a probing node while the probed interface resides on a probed node.

If the probed interface receives the ICMP Echo Request message, it returns an ICMP Echo Reply. When the probing interface receives the ICMP Echo Reply, it has verified bidirectional connectivity between the probing and probed interfaces. Specifically, it has verified that:

This document describes a network diagnostic tool called PROBE. PROBE is similar to PING in that it can be used to query the status of a probed interface, but it differs from PING in that it does not require bidirectional connectivity between the probing and probed interfaces. Instead, PROBE requires bidirectional connectivity between the probing interface and a proxy interface. The proxy interface can reside on the same node as the probed interface, or it can reside on a node to which the probed interface is directly connected. Section 5 of this document describes scenarios in which this characteristic is useful.

Like PING, PROBE executes on a probing node. It sends an ICMP Extended Echo Request message from a local interface, called the probing interface, to a proxy interface. The proxy interface resides on a proxy node.

The ICMP Extended Echo Request contains an ICMP Extension Structure and the ICMP Extension Structure contains an Interface Identification Object. The Interface Identification Object identifies the probed interface. The probed interface can reside on or directly connect to the proxy node.

When the proxy interface receives the ICMP Extended Echo Request, the proxy node executes access control procedures. If access is granted, the proxy node determines the status of the probed interface and returns an ICMP Extended Echo Reply message. The ICMP Extended Echo Reply indicates the status of the probed interface.

If the probed interface resides on the proxy node, PROBE determines the status of the probed interface as it would determine its oper-status [RFC8343]. If oper-status is equal to 'up' (1), PROBE reports that the probed interface is active. Otherwise, PROBE reports that the probed interface is inactive.

If the probed interface resides on a node that is directly connected to the proxy node, and the probed interface appears in the IPv4 Address Resolution Protocol (ARP) table [RFC0826] or IPv6 Neighbor Cache [RFC4861], PROBE reports interface reachability. Otherwise, PROBE reports that the table entry does not exist.

1.1. Terminology

This document uses the following terms:

  • Probing interface: The interface that sends the ICMP Extended Echo Request.

  • Probing node: The node upon which the probing interface resides.

  • Proxy interface: The interface to which the ICMP Extended Echo Request message is sent.

  • Proxy node: The node upon which the proxy interface resides.

  • Probed interface: The interface whose status is being queried.

  • Probed node: The node upon which the probed interface resides. If the proxy interface and the probed interface reside upon the same node, the proxy node is also the probed node. Otherwise, the proxy node is directly connected to the probed node.

1.2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

2. ICMP Extended Echo Request

The ICMP Extended Echo Request message is defined for both ICMPv4 and ICMPv6. Like any ICMP message, the ICMP Extended Echo Request message is encapsulated in an IP header. The ICMPv4 version of the Extended Echo Request message is encapsulated in an IPv4 header, while the ICMPv6 version is encapsulated in an IPv6 header.

Figure 1 depicts the ICMP Extended Echo Request message.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |     Code      |          Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Identifier          |Sequence Number|   Reserved  |L|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   ICMP Extension Structure
   +-+-+-+-+-
   |   [Data...]
Figure 1: ICMP Extended Echo Request Message

IP Header fields:

ICMP fields:

Section 7 of [RFC4884] defines the ICMP Extension Structure. As per RFC 4884, the Extension Structure contains exactly one Extension Header followed by one or more objects. When applied to the ICMP Extended Echo Request message, the Extension Object(s) define the operation to perform. For the operations in this memo, the ICMP Extension Structure MUST contain exactly one instance of the Interface Identification Object (Section 2.1), and the ICMP Extension Structure does not cover the rest of the packet; it ends at the end of the single Interface Identification Object, and what follows is simply optional data. The behavior when it contains a different Extension Object is not defined by this memo but may be defined in the future.

If the L-bit is set, the Interface Identification Object can identify the probed interface by name, index, or address. If the L-bit is clear, the Interface Identification Object MUST identify the probed interface by address.

If the Interface Identification Object identifies the probed interface by address, that address can be a member of any address family. For example, an ICMPv4 Extended Echo Request message can carry an Interface Identification Object that identifies the probed interface by IPv4, IPv6, or IEEE 802 address. Likewise, an ICMPv6 Extended Echo Request message can carry an Interface Identification Object that identifies the probed interface by IPv4, IPv6, or IEEE 802 address.

The Interface Identification Object MAY be followed by an optional data section, which is not interpreted but is simply present to be copied to the ICMP Extended Echo Reply.

2.1. Interface Identification Object

The Interface Identification Object identifies the probed interface by name, index, or address. Like any other ICMP Extension Object, it contains an Object Header and Object Payload. The Object Header contains the following fields:

  • Class-Num: Interface Identification Object. The value is 3.

  • C-Type: Values are (1) Identifies Interface by Name, (2) Identifies Interface by Index, and (3) Identifies Interface by Address.

  • Length: Length of the object, measured in octets, including the Object Header and Object Payload.

If the Interface Identification Object identifies the probed interface by name, the Object Payload MUST be the interface name as defined in [RFC8343]. If the Object Payload would not otherwise terminate on a 32-bit boundary, it MUST be padded with ASCII NUL characters, adjusting the Length accordingly.

If the Interface Identification Object identifies the probed interface by index, the length is equal to 8 and the payload contains the if-index [RFC8343].

If the Interface Identification Object identifies the probed interface by address, the payload is 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                | Address Length|   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                Address   ....
Figure 2: Interface Identification Object - C-Type 3 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. All values found in the IANA registry of Address Family Numbers (available from [IANA.address-family-numbers]) are valid in this field.

  • Address Length: Number of significant bytes contained by the Address field. (The Address field contains significant bytes and padding bytes.)

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

  • Address: This variable-length field represents an address associated with the probed interface. If the address field would not otherwise terminate on a 32-bit boundary, it MUST be padded with zeroes.

3. ICMP Extended Echo Reply

The ICMP Extended Echo Reply message is defined for both ICMPv4 and ICMPv6. Like any ICMP message, the ICMP Extended Echo Reply message is encapsulated in an IP header. The ICMPv4 version of the Extended Echo Reply message is encapsulated in an IPv4 header, while the ICMPv6 version is encapsulated in an IPv6 header.

Figure 3 depicts the ICMP Extended Echo Reply message.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |     Code      |          Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Identifier          |Sequence Number|State|Res|A|4|6|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   ICMP Extension Structure
   +-+-+-+-+-
   |   [Data...]
Figure 3: ICMP Extended Echo Reply Message

IP Header fields:

ICMP fields:

4. ICMP Message Processing

When a node receives an ICMP Extended Echo Request message and any of the following conditions apply, the node MUST silently discard the incoming message:

Otherwise, when a node receives an ICMPv4 Extended Echo Request, it MUST format an ICMP Extended Echo Reply as follows:

When a node receives an ICMPv6 Extended Echo Request, it MUST format an ICMPv6 Extended Echo Reply as follows:

In either case, the responding node MUST do the following:

4.1. Code Field Processing

The Code field MUST be set to (1) Malformed Query if any of the following conditions apply:

  • The ICMP Extended Echo Request does not include an ICMP Extension Structure.

  • The ICMP Extension Structure does not include exactly one Interface Identification Object.

  • The ICMP Extension Structure checksum is 0 or incorrect.

  • The L-bit is clear and the Interface Identification Object identifies the probed interface by name or if-index.

  • The query is otherwise malformed.

The Code field MUST be set to (2) No Such Interface if the L-bit is set and the ICMP Extension Structure does not identify an interface that resides on the proxy node.

The Code field MUST be set to (3) No Such Table Entry if the L-bit is clear and the address found in the Interface Identification Object does not appear in the IPv4 Address Resolution Protocol (ARP) table or the IPv6 Neighbor Cache.

The Code field MUST be set to (4) Multiple Interfaces Satisfy Query if any of the following conditions apply:

  • The L-bit is set and the ICMP Extension Structure identifies more than one interface that resides in the proxy node.

  • The L-bit is clear and the address found in the Interface Identification Object maps to multiple IPv4 ARP or IPv6 Neighbor Cache entries.

Otherwise, the Code field MUST be set to (0) No Error.

5. Use Cases

In the scenarios listed below, network operators can use PROBE to determine the status of a probed interface but cannot use PING for the same purpose. In all scenarios, assume bidirectional connectivity between the probing and proxy interfaces. However, bidirectional connectivity between the probing and probed interfaces is lacking.

6. Updates to RFC 4884

Section 4.6 of [RFC4884] provides a list of extensible ICMP messages (i.e., messages that can carry the ICMP Extension Structure). This document adds the ICMP Extended Echo Request message and the ICMP Extended Echo Reply message to that list.

7. Change History

7.1. Changes from RFC 8335

This document updates [RFC8335] to clarify the handling of extra data beyond the ICMP Extension Structure, that data is echoed in the response packet, and checksum handling in the ICMP Extension Structure.

Specifically,

  • Updated Figure 1 to reflect the presence of the ICMP Extension Object and additional data.

  • Updated Section 2 to mention the ICMP Extension Structure checksum, and extra verbosity about how the Extension Structure does not cover the rest of the packet.

  • Updated Figure 3 to reflect the presence of the ICMP Extension Structure and additional data.

  • Added a step in Section 4 about copying data from the request to the response.

  • Added a step in Section 4.1 about validating the ICMP Extension Structure checksum.

  • Added section Appendix A.1 to suggest human-readable display of PROBE responses

  • Clarified in Section 2.1 that the length of an ifName Object is adjusted when padding is added.

7.2. Changes from draft-fenner-intarea-probe-clarification-00

  • Changed "NULL" to "NUL" when referring to the ASCII control character, per RFC20.

  • Consistently refer to interface name and index using their yang names, not SNMP names.

  • Added [] around the Data following the ICMP Extension Structure in Figure 1 and Figure 3 to indicate that it is optional.

7.3. Changes from draft-fenner-intarea-probe-clarification-01

  • Updated the section on ICMP Extension header format to say that different ICMP Extension Option headers may be present, and if they are, the mechanism is not as specified in this memo.

8. IANA Considerations

IANA is requested to update the references for the below actions from [RFC8335] to refer to this document.

IANA has performed the following actions:

All codes mentioned above are assigned on an FCFS basis with a range of 0-255.

9. Security Considerations

The following are legitimate uses of PROBE:

However, malicious parties can use PROBE to obtain additional information. For example, a malicious party can use PROBE to discover interface names. Having discovered an interface name, the malicious party may be able to infer additional information. Additional information may include:

Understanding this risk, network operators establish policies that restrict access to ICMP Extended Echo functionality. In order to enforce these policies, nodes that support ICMP Extended Echo functionality MUST support the following configuration options:

When a node receives an ICMP Extended Echo Request message that it is not configured to support, it MUST silently discard the message. See Section 4 for details.

PROBE must not leak information about one Virtual Private Network (VPN) into another. Therefore, when a node receives an ICMP Extended Echo Request and the proxy interface is in a different VPN than the probed interface, the node MUST return an ICMP Extended Echo Reply with error code equal to (2) No Such Interface.

In order to protect local resources, implementations SHOULD rate-limit incoming ICMP Extended Echo Request messages.

10. References

10.1. Normative References

[RFC0792]
Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, DOI 10.17487/RFC0792, , <https://www.rfc-editor.org/rfc/rfc792>.
[RFC0826]
Plummer, D., "An Ethernet Address Resolution Protocol: Or Converting Network Protocol Addresses to 48.bit Ethernet Address for Transmission on Ethernet Hardware", STD 37, RFC 826, DOI 10.17487/RFC0826, , <https://www.rfc-editor.org/rfc/rfc826>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/rfc/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, , <https://www.rfc-editor.org/rfc/rfc4443>.
[RFC4861]
Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, , <https://www.rfc-editor.org/rfc/rfc4861>.
[RFC4884]
Bonica, R., Gan, D., Tappan, D., and C. Pignataro, "Extended ICMP to Support Multi-Part Messages", RFC 4884, DOI 10.17487/RFC4884, , <https://www.rfc-editor.org/rfc/rfc4884>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <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, , <https://www.rfc-editor.org/rfc/rfc8335>.
[RFC8343]
Bjorklund, M., "A YANG Data Model for Interface Management", RFC 8343, DOI 10.17487/RFC8343, , <https://www.rfc-editor.org/rfc/rfc8343>.

10.2. Informative References

[IANA.address-family-numbers]
IANA, "Address Family Numbers", <https://www.iana.org/assignments/address-family-numbers>.
[RFC2151]
Kessler, G. and S. Shepard, "A Primer On Internet and TCP/IP Tools and Utilities", FYI 30, RFC 2151, DOI 10.17487/RFC2151, , <https://www.rfc-editor.org/rfc/rfc2151>.
[RFC4594]
Babiarz, J., Chan, K., and F. Baker, "Configuration Guidelines for DiffServ Service Classes", RFC 4594, DOI 10.17487/RFC4594, , <https://www.rfc-editor.org/rfc/rfc4594>.

Appendix A. The PROBE Application

The PROBE application accepts input parameters, sets a counter, and enters a loop to be exited when the counter is equal to 0. On each iteration of the loop, PROBE emits an ICMP Extended Echo Request, decrements the counter, sets a timer, and waits. The ICMP Extended Echo Request includes an Identifier and a Sequence Number.

If an ICMP Extended Echo Reply carrying the same Identifier and Sequence Number arrives, PROBE relays information returned by that message to its user. However, on each iteration of the loop, PROBE waits for the timer to expire regardless of whether an Extended Echo Reply message arrives.

PROBE accepts the following parameters:

Count is a positive integer whose default value is 3. Count determines the number of times that PROBE iterates through the above-mentioned loop.

Wait is a positive integer whose minimum and default values are 1. Wait determines the duration of the above-mentioned timer, measured in seconds.

Probing Interface Address specifies the Source Address of the ICMP Extended Echo Request. The Probing Interface Address MUST be a unicast address and MUST identify an interface that resides on the probing node.

The Proxy Interface Address identifies the interface to which the ICMP Extended Echo Request message is sent. It must be an IPv4 or IPv6 unicast address. If it is an IPv4 address, PROBE emits an ICMPv4 message. If it is an IPv6 address, PROBE emits an ICMPv6 message.

Local is a boolean value. It is TRUE if the proxy and probed interfaces both reside on the same node. Otherwise, it is FALSE.

The Probed Interface Identifier identifies the probed interface. It is one of the following:

If the Probed Interface Identifier is an address, it does not need to be of the same address family as the proxy interface address. For example, PROBE accepts an IPv4 Proxy Interface Address and an IPv6 Probed Interface Identifier.

A.1. Information Display

For the PING application, the primary available piece of information is the fact that we received an ICMP Echo Reply. Therefore, the appropriate information to display is all of the available information about the received reply, e.g., size, ttl, etc. However, with PROBE, the primary piece of information is the reported status of the probed interface: the code, status, A, 4, and 6 fields. It's appropriate to convert the combination of the returned values into a "human-readable" response.

For example, an application may perform these steps:

  • If the code field is non-zero, print the code value as described in Section 3.

  • If the code field is zero, then if the L field sent is zero, print the state value as described in Section 3.

  • Otherwise, the L field sent is 1; print the state represented by the A, 4, and 6 bits. Sample textual translations for these bits are shown in Table 1.

Table 1: Sample translations for bit settings
A 4 6 Text
0 0 0 Interface inactive
1 0 0 Interface active, with no ipv4 or ipv6 running
1 0 1 Interface active, with ipv6 running
1 1 0 Interface active, with ipv4 running
1 1 1 Interface active, with ipv4 and ipv6 running

Acknowledgments

Thanks to Sowmini Varadhan, Jeff Haas, Carlos Pignataro, Jonathan Looney, Dave Thaler, Mikio Hara, Joel Halpern, Yaron Sheffer, Stefan Winter, Jean-Michel Combes, Amanda Barber, and Joe Touch for their thoughtful review of this document.

Authors' Addresses

Bill Fenner (editor)
Arista Networks
5453 Great America Parkway
Santa Clara, California 95054
United States of America
Ron Bonica
Juniper Networks
2251 Corporate Park Drive
Herndon, Virginia 20171
United States of America
Reji Thomas
Arista Networks
Global Tech Park
Bangalore 560103
Karnataka
India
Jen Linkova
Google
1600 Amphitheatre Parkway
Mountain View, California 94043
United States of America
Chris Lenart
Verizon
22001 Loudoun County Parkway
Ashburn, Virginia 20147
United States of America
Mohamed Boucadair
Orange
Rennes 35000
France