More Features for TWAMP
draft-morton-ippm-more-twamp-02

Status of this Memo

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Abstract

The IETF is completing its work on TWAMP - the Two-Way Active Measurement Protocol. This memo describes additional features for TWAMP, essentially the ability to use different security modes in the TWAMP-Control and TWAMP-Test protocols.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].

Table of Contents

1.  Introduction
2.  Purpose and Scope
3.  TWAMP Control Extensions
    3.1.  Extended Connection Setup
4.  Extended TWAMP Test
    4.1.  Sender Behavior
        4.1.1.  Packet Timings
        4.1.2.  Packet Format and Content
    4.2.  Reflector Behavior
5.  Security Considerations
6.  IANA Considerations
    6.1.  Registry Specification
    6.2.  Registry Management
    6.3.  Experimental Numbers
    6.4.  Initial Registry Contents
7.  Acknowledgements
8.  References
    8.1.  Normative References
    8.2.  Informative References
§  Authors' Addresses
§  Intellectual Property and Copyright Statements

1.  Introduction

The IETF is completing its work on TWAMP - the Two-Way Active Measurement Protocol [I‑D.ietf‑ippm‑twamp] (Babiarz, J., “A Two-way Active Measurement Protocol (TWAMP),” August 2008.), which is an extension to the One-way Active Measurement Protocol, OWAMP [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.). The TWAMP specification gathered wide review as it approached completion, and the by-products were several recommendations for new features in TWAMP. There are a growing number TWAMP implementations at present, and wide-spread usage is expected. There are even devices emerging that test implementations for protocol compliance.

This memo describes additional features for TWAMP, such as the ability to use different security modes in the TWAMP-Control and TWAMP-Test protocols.

The relationship between this memo and the TWAMP is intended to be an update to the TWAMP RFC when published.

2.  Purpose and Scope

The purpose of this memo is to specify additional functions and features for TWAMP [I‑D.ietf‑ippm‑twamp] (Babiarz, J., “A Two-way Active Measurement Protocol (TWAMP),” August 2008.). The features and extensions were vetted before adoption in this memo.

The scope of the memo is limited to specifications of the following features:

1. Extension of the modes of operation through assignment of new values in the Mode field (see section 3.1 of [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.)), while retaining backward compatibility with TWAMP [I‑D.ietf‑ippm‑twamp] (Babiarz, J., “A Two-way Active Measurement Protocol (TWAMP),” August 2008.) implementations. These values add the ability to use different security modes in the TWAMP-Control and TWAMP-Test protocols. The motivation for this extension is to permit the low packet rate TWAMP-Control protocol to utilize a stronger mode of integrity protection than that used in the TWAMP-Test protocol.

(other items may be added)

3.  TWAMP Control Extensions

TWAMP-Control protocol is a derivative of the OWAMP-Control protocol, and provides two-way measurement capability. All TWAMP Control messages are similar in format and follow similar guidelines to those defined in section 3 of [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.) with the exceptions described in TWAMP [I‑D.ietf‑ippm‑twamp] (Babiarz, J., “A Two-way Active Measurement Protocol (TWAMP),” August 2008.), and in the following sections.

All OWAMP-Control messages apply to TWAMP-Control, except for the Fetch Session command.

3.1.  Extended Connection Setup

TWAMP connection establishment follows the same procedure defined in section 3.1 of [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.). The extended modes assign three new bit positions (and values) to allow the Test protocol security mode to differ from the Control protocol mode. With this extension, the complete set of TWAMP values are as follows:

Value  Description             Reference/Explanation
0      Reserved
1      Unauthenticated         RFC4656, Section 3.1
2      Authenticated           RFC4656, Section 3.1
4      Encrypted               RFC4656, Section 3.1
8      Unauth. TEST protocol,  new bit position (3)
       Encrypted CONTROL

In the original OWAMP mode field, setting bit positions 0, 1 or 2 indicated the security mode of the Control protocol, and the Test protocol inherited the same mode (see section 4 of [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.)). In this extension to TWAMP, setting a higher mode field bit position (3) SHALL discontinue the inheritance of the security mode in the Test protocol, and each protocol’s mode SHALL be specified explicitly. When the desired TWAMP Test protocol mode is identical to the Control Session mode, the corresponding mode bit (position 0, 1 or 2) SHALL be set. The table below gives the various combinations that are now permissible in TWAMP, where the Test protocol may use one of the modes in each column corresponding to a Control mode.

-------------------------------------------------------
Protocol | Permissible Mode Combinations (mode bit set)
-------------------------------------------------------
Control  |    Unauth.(0)|  Auth.(1)|  Encrypted (2)
-------------------------------------------------------
         |    Unauth.(0)|          |   Unauth.  (3)
         ----------------------------------------------
Test     |              |  Auth.(1)|
         ----------------------------------------------
         |              |          |  Encrypted (2)
-------------------------------------------------------

Note that the TWAMP-Control protocol security measures are identical in the Authenticated and Encrypted Modes. Therefore, only one new mode is needed to cover all mixed secuity modes that are possible.

The value of the Modes field sent by the Server is the bit-wise OR of the mode values that it is willing to support during this session. Thus, the last four bits of the Modes 32-bit field are used. The first 28 bits MUST be zero. A client conforming to this version of the specification MUST ignore the values in the first 28 bits of the Modes value. (This way, the bits are available for future protocol extensions.)

Other ways in which TWAMP extends OWAMP are described in [I‑D.ietf‑ippm‑twamp] (Babiarz, J., “A Two-way Active Measurement Protocol (TWAMP),” August 2008.).

4.  Extended TWAMP Test

The TWAMP test protocol is similar to the OWAMP [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.) test protocol with the exception that the Session-Reflector transmits test packets to the Session-Sender in response to each test packet it receives. TWAMP [I‑D.ietf‑ippm‑twamp] (Babiarz, J., “A Two-way Active Measurement Protocol (TWAMP),” August 2008.) defines two different test packet formats, one for packets transmitted by the Session-Sender and one for packets transmitted by the Session-Reflector. As with OWAMP-Test protocol there are three security modes: unauthenticated, authenticated, and encrypted. The extension to TWAMP makes it possible to specify these modes independently from the mode used in the TWAMP-Control protocol.

4.1.  Sender Behavior

This section describes extensions to the behavior of the TWAMP Sender.

4.1.1.  Packet Timings

The Send Schedule is not utilized in TWAMP, and there are no extensions defined in this memo.

4.1.2.  Packet Format and Content

The Session Sender packet format and content follow the same procedure and guidelines as defined in section 4.1.2 of [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.), with the following exceptions:

• the Send Schedule is not used, and
• the support of additional security mode combinations defined in section 3.1 of this memo.

4.2.  Reflector Behavior

The TWAMP Reflector follows the procedures and guidelines in section 4.2 of [I‑D.ietf‑ippm‑twamp] (Babiarz, J., “A Two-way Active Measurement Protocol (TWAMP),” August 2008.), with the following extensions:

• the support of additional security mode combinations defined in section 3.1 of this memo.

5.  Security Considerations

These extended modes of operation permit stronger integrity protection on the TWAMP-Control protocol while simultaneously emphasizing accuracy or efficiency on the TWAMP-Test protocol, thus enhancing overall security when compared to the previous options.

The security considerations that apply to any active measurement of live networks are relevant here as well. See [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.) and [I‑D.ietf‑ippm‑twamp] (Babiarz, J., “A Two-way Active Measurement Protocol (TWAMP),” August 2008.).

6.  IANA Considerations

This memo adds three security mode combinations to the OWAMP-Control specification[RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.), and describes behavior when the new modes are used. This memo requests creation an IANA registry for the TWAMP Mode field. This field is a recognized extension mechanism for TWAMP.

6.1.  Registry Specification

IANA is requested to create a TWAMP-Modes registry. TWAMP-Modes are specified in TWAMP Server Greeting messages and Set-up Response messages consistent with section 3.1 of [RFC4656] (Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” September 2006.), and extended by this memo. Modes are indicated by setting bits in the 32-bit Modes field. Thus, this registry can contain a total of 32 possible values.

6.2.  Registry Management

Because the Modes registry can contain only thirty-two values, and because TWAMP is an IETF protocol, this registry must be updated only by "IETF Consensus" as specified in [RFC2434] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” October 1998.)(an RFC documenting registry use that is approved by the IESG). For the Modes registry, we expect that new features will be assigned using monotonically increasing bit positions and in the range [0-31] and the corresponding values, unless there is a good reason to do otherwise.

6.3.  Experimental Numbers

No experimental values are currently assigned for the Modes Registry.

6.4.  Initial Registry Contents

TWAMP Modes Registry

Value  Description             Semantics Definition
0      Reserved

1      Unauthenticated         RFC4656, Section 3.1

2      Authenticated           RFC4656, Section 3.1

4      Encrypted               RFC4656, Section 3.1

8      Unauth. TEST protocol,  this document, Section 3.1
       Encrypted CONTROL

7.  Acknowledgements

The authors would like to thank Len Ciavattone for helpful review and comments.

8.  References

8.1. Normative References

8.2. Informative References

Authors' Addresses

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