OWAMP and TWAMP Well-Known Port Assignments
draft-morton-ippm-port-twamp-test-01

Abstract

This memo explains the motivation and describes the re-assignment of well-known ports for the OWAMP and TWAMP protocols for control and measurement, and clarifies the meaning and composition of these standards track protocol names for the industry.

The memo updates RFC 4656 and RFC 5357, in terms of the UDP well-known port assignments.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on January 22, 2018.

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Table of Contents

• 1. Introduction
• 2. Requirements Language
• 3. Scope
• 4. Definitions
• 5. New Well-Known Ports
• 5.1. Impact on TWAMP-Control Protocol
• 5.2. Impact on OWAMP-Control Protocol
• 5.3. Impact on OWAMP/TWAMP-Test Protocols
• 6. Security Considerations
• 7. IANA Considerations
• 8. Contributors
• 9. Acknowledgements
• 10. References
• 10.1. Normative References
• 10.2. Informative References
• Authors' Addresses

1. Introduction

The IETF IP Performance Metrics (IPPM) working group first developed the One-Way Active Measurement Protocol, OWAMP, specified in [RFC4656]. Further protocol development to support testing resulted in the Two-Way Active Measurement Protocol, TWAMP, specified in [RFC5357].

Both OWAMP and TWAMP require the implementation of a control and mode negotiation protocol (OWAMP-Control and TWAMP-Control) which employs the reliable transport services of TCP (including security configuration and key derivation). The control protocols arrange for the configuration and management of test sessions using the associated test protocol (OWAMP-Test or TWAMP-Test) on UDP transport.

This memo recognizes the value of assigning a well-known UDP port to the *-Test protocols, and that this goal can easily be arranged through port re-assignments.

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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. Scope

The scope of this memo is to re-allocate well-known ports for the UDP Test protocols that compose necessary parts of their respective standards track protocols, OWAMP and TWAMP, along with clarifications of the complete protocol composition for the industry.

The memo updates [RFC4656] and [RFC5357], in terms of the UDP well-known port assignments.

4. Definitions

This section defines key terms and clarifies the required composition of the OWAMP and TWAMP standards-track protocols.

OWAMP-Control is the protocol defined in Section 3 of [RFC4656].

OWAMP-Test is the protocol defined in Section 4 of [RFC4656].

OWAMP is described in a direct quote from Section 1.1 of[RFC4656]: "OWAMP actually consists of two inter-related protocols: OWAMP-Control and OWAMP-Test." A similar sentence appears in Section 2 of [RFC4656]. Since the consensus of many dictionary definitions of "consist" is "composed or made up of", implementation of both OWAMP-Control and OWAMP-Test are REQUIRED for standards-track OWAMP specified in [RFC4656].

TWAMP-Control is the protocol defined in Section 3 of [RFC5357].

TWAMP-Test is the protocol defined in Section 4 of [RFC5357].

TWAMP is described in a direct quote from Section 1.1 of [RFC5357]: "Similar to OWAMP [RFC4656], TWAMP consists of two inter-related protocols: TWAMP-Control and TWAMP-Test." Since the consensus of many dictionary definitions of "consist" is "composed or made up of", implementation of both TWAMP-Control and TWAMP-Test are REQUIRED for standards-track TWAMP specified in [RFC5357].

TWAMP Light is an idea described in Informative Appendix I of [RFC5357], and includes an un-specified control protocol (possibly communicating through non-standard means) combined with the TWAMP-Test protocol. The TWAMP Light idea was relegated to the Appendix because it failed to meet the requirements for IETF protocols (there are no specifications for negotiating this form of operation, and no specifications for mandatory-to-implement security features), as described in the references below:

• Lars Eggert's Area Director review [LarsAD], where he pointed out that having two variants of TWAMP, Light and Complete (called standards track TWAMP here), required a protocol mechanism to negotiate which variant will be used. See Lars' comment on Sec 5.2. The working group consensus was to place the TWAMP Light description in Appendix I, and to refer to the Appendix only as an "incremental path to adopting TWAMP, by implementing the TWAMP-Test protocol first".
• Tim Polk's DISCUSS Ballot, which points out that TWAMP Light was an incomplete specification because the key required for authenticated and encrypted modes depended on the TWAMP-Control Session key. See Tim's DISCUSS on 2008-07-16 [TimDISCUSS]. Additional requirement statements were added in the Appendix to address Tim's DISCUSS Ballot (see the last three paragraphs of Appendix I in [RFC5357]).

Since the idea of TWAMP Light clearly includes the TWAMP-Test component of TWAMP, it is considered reasonable for future systems to use the TWAMP-Test well-known UDP port (whose re-allocated assignment is requested here). Clearly, the TWAMP Light idea envisions many components and communication capabilities beyond TWAMP-Test (implementing the security requirements, for example), otherwise the Appendix would be one sentence long (equivocating TWAMP Light with TWAMP-Test only).

5. New Well-Known Ports

Originally, both TCP and UDP well-known ports were assigned to the control protocols that are essential components of standards track OWAMP and TWAMP.

Since OWAMP-Control and TWAMP-Control require TCP transport, they cannot make use of the UDP ports which were originally assigned. However, test sessions using OWAMP-Test or TWAMP-Test operate on UDP transport. It may simplify some operations to have a well-known port available for the Test protocols as a default port, and this memo requests re-assignment of the UDP well-known port from the Control protocol to the Test protocol (see the IANA Considerations Section 7).

5.1. Impact on TWAMP-Control Protocol

Section 3.5 [RFC5357] describes the detailed process of negotiating the Receiver Port number, on which the TWAMP Session-Reflector will send and receive TWAMP-Test packets. The Control-Client, acting on behalf of the Session-Sender, proposes the Receiver port number from the Dynamic Port range [RFC6335]:

• "The Receiver Port is the desired UDP port to which TWAMP-Test packets will be sent by the Session-Sender (the port where the Session-Reflector is asked to receive test packets). The Receiver Port is also the UDP port from which TWAMP-Test packets will be sent by the Session-Reflector (the Session-Reflector will use the same UDP port to send and receive packets)."

It is possible that the proposed Receiver Port may be not available, e.g., the port is in use by another test session or another application. In this case:

• "... the Server at the Session-Reflector MAY suggest an alternate and available port for this session in the Port field. The Control-Client either accepts the alternate port, or composes a new Session-Request message with suitable parameters. Otherwise, the Server uses the Accept field to convey other forms of session rejection or failure to the Control Client and MUST NOT suggest an alternate port; in this case, the Port field MUST be set to zero."

A Control Client that supports use of the allocated TWAMP-Test Receiver Port Section 7 MAY request to use that port number in the Request-TW-Session Command. If the Server does not support the allocated TWAMP-Test Receiver Port, then it sends an alternate port number in the Accept-Session message with Accept field = 0. Thus the deployment of the allocated TWAMP Receiver Port number is backward compatible with existing TWAMP-Control solutions that are based on [RFC5357]. Of course, use of a UDP port number chosen from the Dynamic Port range [RFC6335] will help to avoid the situation when the Control-Client or Server finds the proposed port being already in use.

5.2. Impact on OWAMP-Control Protocol

As described above, an OWAMP Control Client that supports use of the allocated OWAMP-Test Receiver Port Section 7 MAY request to use that port number in the Request-Session Command. If the Server does not support the allocated OWAMP-Test Receiver Port (or does not have the port available), then it sends an alternate port number in the Accept-Session message with Accept field = 0. Further exchanges proceed as already specified.

5.3. Impact on OWAMP/TWAMP-Test Protocols

OWAMP/TWAMP-Test may be used to measure IP performance metrics in an Equal Cost Multipath (ECMP) environment. Though algorithms to balance IP flows among available paths have not been standardized, the most common is the five-tuple that uses destination IP address, source IP address, protocol type, destination port number, and source port number. When attempting to monitor different paths in ECMP network, it is sufficient to vary only one of five parameters, e.g. the source port number. Thus, there will be no negative impact on ability to arrange concurrent OWAMP/TWAMP test sessions between the same test points to monitor different paths in the ECMP network when using the re-allocated UDP port number as the Receiver Port, as use of the port is optional.

6. Security Considerations

The security considerations that apply to any active measurement of live paths are relevant here as well (see [RFC4656] and [RFC5357]).

When considering privacy of those involved in measurement or those whose traffic is measured, the sensitive information available to potential observers is greatly reduced when using active techniques which are within this scope of work. Passive observations of user traffic for measurement purposes raise many privacy issues. We refer the reader to the security and privacy considerations described in the Large Scale Measurement of Broadband Performance (LMAP) Framework [RFC7594], which covers both active and passive techniques.

The registered UDP port as the Receiver Port for OWAMP/TWAMP-Test could become a target of denial-of-service (DoS) or used to aid man-in-the-middle (MITM) attacks. To improve protection from the DoS following methods are recommended:

• filtering access to the OWAMP/TWAMP Receiver Port by access list;
• using a non-globally routable IP address for the OWAMP/TWAMP Session-Reflector address.

A MITM attack may try to modify the content of the OWAMP/TWAMP-Test packets in order to alter the measurement results. However, an implementation can use authenticated mode to detect modification of data. In addition, use encrypted mode to prevent eavesdropping and un-detected modification of the OWAMP/TWAMP-Test packets.

7. IANA Considerations

This memo requests re-allocation of two UDP port numbers from the System Ports range [RFC6335]. Specifically, this memo requests that IANA re-allocate UDP ports 861 and 862 as shown below, leaving the TCP port assignments as-is:

+------------+-------+---------+----------------------+-------------+
| Service    | Port  | Transpo | Description          | Reference   |
| Name       | Numbe | rt Prot |                      |             |
|            | r     | ocol    |                      |             |
+------------+-------+---------+----------------------+-------------+
| owamp-     | 861   | tcp     | OWAMP-Control        | [RFC4656]   |
| control    |       |         |                      |             |
| owamp-test | 861   | udp     | OWAMP-Test           | [RFCXXXX]   |
|            |       |         |                      |             |
| twamp-     | 861   | tcp     | TWAMP-Control        | [RFC5357]   |
| control    |       |         |                      |             |
| twamp-test | 862   | udp     | TWAMP-Test Receiver  | [RFCXXXX]   |
|            |       |         | Port                 |             |
+------------+-------+---------+----------------------+-------------+

Table 1 Re-allocated OWAMP and TWAMP Ports

where RFCXXXX is this memo when published.

8. Contributors

Richard Foote and Luis M. Contreras made notable contributions on this topic.

9. Acknowledgements

The authors thank the IPPM working group for their rapid review; also Muthu Arul Mozhi Perumal and Luay Jalil for their participation and suggestions.

10. References

10.1. Normative References

10.2. Informative References

Authors' Addresses