Network Working Group A. Morton
Request for Comments: 5618 AT&T Labs
Updates: 5357 K. Hedayat
Category: Standards Track EXFO
August 2009
Mixed Security Mode for the Two-Way Active Measurement Protocol (TWAMP)
Abstract
This memo describes a simple extension to TWAMP (the Two-Way Active
Measurement Protocol). The extension adds the option to use
different security modes in the TWAMP-Control and TWAMP-Test
protocols simultaneously. The memo also describes a new IANA
registry for additional features, called the TWAMP Modes registry.
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
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Morton & Hedayat Standards Track [Page 1]RFC 5618 TWAMP Extensions August 2009
Table of Contents
1. Introduction ....................................................2
1.1. Requirements Language ......................................3
2. Purpose and Scope ...............................................3
3. TWAMP Control Extensions ........................................3
3.1. Extended Control Connection Setup ..........................3
4. Extended TWAMP Test .............................................5
4.1. Sender Behavior ............................................5
4.1.1. Packet Timings ......................................5
4.1.2. Packet Format and Content ...........................5
4.2. Reflector Behavior .........................................6
5. Security Considerations .........................................6
6. IANA Considerations .............................................6
6.1. Registry Specification .....................................6
6.2. Registry Management ........................................6
6.3. Experimental Numbers .......................................7
6.4. Initial Registry Contents ..................................7
7. Acknowledgements ................................................7
8. Normative References ............................................7
1. Introduction
The Two-Way Active Measurement Protocol (TWAMP) [RFC5357] is an
extension of the One-Way Active Measurement Protocol (OWAMP)
[RFC4656]. The TWAMP specification gathered wide review as it
approached completion, and the by-products were several
recommendations for new features in TWAMP. There is a growing number
of TWAMP implementations at present, and widespread usage is
expected. There are even devices that are designed to test
implementations for protocol compliance.
This memo describes a simple extension for TWAMP: the option to use
different security modes in the TWAMP-Control and TWAMP-Test
protocols (mixed security mode). It also describes a new IANA
registry for additional features, called the TWAMP Modes registry.
When the Server and Control-Client have agreed to use the mixed
security mode during control connection setup, then the Control-
Client, the Server, the Session-Sender, and the Session-Reflector
MUST all conform to the requirements of this mode as described in
Sections 3, 4, and 5.
This memo updates [RFC5357].
Morton & Hedayat Standards Track [Page 2]RFC 5618 TWAMP Extensions August 2009
1.1. 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 [RFC2119].
2. Purpose and Scope
The purpose of this memo is to describe and specify an extension for
TWAMP [RFC5357], and to request the establishment of a registry for
future TWAMP extensions.
The scope of the memo is limited to specifications of the following:
o Extension of the modes of operation through assignment of one new
value in the Modes field (see Section 3.1 of [RFC4656]), while
retaining backward compatibility with TWAMP [RFC5357]
implementations. This value adds the OPTIONAL 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.
3. TWAMP Control Extensions
The TWAMP-Control protocol is a derivative of the OWAMP-Control
protocol, and coordinates a two-way measurement capability. All
TWAMP-Control messages are similar in format and follow similar
guidelines to those defined in Section 3 of [RFC4656], with the
exceptions described in TWAMP [RFC5357] and in the following
sections.
All OWAMP-Control messages apply to TWAMP-Control, except for the
Fetch-Session command.
3.1. Extended Control Connection Setup
TWAMP-Control connection establishment follows the same procedure
defined in Section 3.1 of [RFC4656]. This extended mode assigns one
new bit position (and value) to allow the Test protocol security mode
to operate in Unauthenticated mode, while the Control protocol
operates in Encrypted mode. With this extension, the complete set of
TWAMP Mode values are as follows:
Morton & Hedayat Standards Track [Page 3]RFC 5618 TWAMP Extensions August 2009
Value Description Reference/Explanation
0 Reserved
1 Unauthenticated RFC 4656, Section 3.1
2 Authenticated RFC 4656, Section 3.1
4 Encrypted RFC 4656, Section 3.1
8 Unauth. TEST protocol, new bit position (3)
Encrypted CONTROL
In the original OWAMP and TWAMP Modes field, setting bit position 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]).
In this extension to TWAMP, when the Control-Client sets Modes Field
bit position 3, it SHALL discontinue the inheritance of the security
mode in the Test protocol, and each protocol's mode SHALL be as
specified below. When the desired TWAMP-Test protocol mode is
identical to the Control Session mode, the corresponding Modes Field
bit (position 0, 1, or 2) SHALL be set by the Control-Client. The
table below gives the various combinations of integrity protection
that are permissible in TWAMP (with this extension). The TWAMP-
Control and TWAMP-Test protocols SHALL use the mode in each column
corresponding to the bit position set in the Modes Field.
--------------------------------------------------------
Protocol | Permissible Mode Combinations (Modes bit set)
--------------------------------------------------------
Control | Unauth.(0)| Auth. == Encrypted (1,2,3)
--------------------------------------------------------
| 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
bit position (3) is needed to convey the single mixed security mode.
The value of the Modes Field sent by the Server in the Server-
Greeting message is the bit-wise OR of the modes (bit positions) that
it is willing to support during this session. Thus, the last four
Morton & Hedayat Standards Track [Page 4]RFC 5618 TWAMP Extensions August 2009
bits of the 32-bit Modes Field are used. When no other features are
activated, the first 28 bits MUST be zero. A client conforming to
this extension of [RFC5357] MAY ignore the values in the first 28
bits of the Modes Field, or it MAY support other features that are
communicated in these bit positions.
Other ways in which TWAMP extends OWAMP are described in [RFC5357].
4. Extended TWAMP Test
The TWAMP-Test protocol is similar to the OWAMP-Test protocol
[RFC4656] with the exception that the Session-Reflector transmits
test packets to the Session-Sender in response to each test packet it
receives. TWAMP [RFC5357] 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 the OWAMP-Test
protocol, there are three security modes that also determine the test
packet format: unauthenticated, authenticated, and encrypted. This
TWAMP extension makes it possible to use TWAMP-Test Unauthenticated
mode regardless of the mode used in the TWAMP-Control protocol.
When the Server has identified the ability to support the mixed
security mode, the Control-Client has selected the mixed security
mode in its Set-Up-Response, and the Server has responded with a zero
Accept field in the Server-Start message, these extensions are
REQUIRED.
4.1. Sender Behavior
This section describes extensions to the behavior of the TWAMP
Session-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 MUST follow the same
procedure and guidelines as defined in Section 4.1.2 of [RFC4656] and
Section 4.1.2 of [RFC5357], with the following exceptions:
o the send schedule is not used, and
o the Session-Sender MUST support the mixed security mode
(Unauthenticated TEST, Encrypted CONTROL, value 8, bit position 3)
defined in Section 3.1 of this memo.
Morton & Hedayat Standards Track [Page 5]RFC 5618 TWAMP Extensions August 2009
4.2. Reflector Behavior
The TWAMP Session-Reflector is REQUIRED to follow the procedures and
guidelines in Section 4.2 of [RFC5357], with the following
extensions:
o the Session-Reflector MUST support the mixed security mode
(Unauthenticated TEST, Encrypted CONTROL, value 8, bit position 3)
defined in Section 3.1 of this memo.
5. Security Considerations
The extended mixed mode of operation permits stronger security/
integrity protection on the TWAMP-Control protocol while
simultaneously emphasizing accuracy or efficiency on the TWAMP-Test
protocol, thus making it possible to increase overall security when
compared to the previous options (when resource constraints would
have forced less security for TWAMP-Control and conditions are such
that use of unauthenticated TWAMP-Test is not a significant concern).
The security considerations that apply to any active measurement of
live networks are relevant here as well. See [RFC4656] and
[RFC5357].
6. IANA Considerations
This memo adds one security mode bit position/value beyond those in
the OWAMP-Control specification [RFC4656], and describes behavior
when the new mode is used. According to this document, IANA created
a registry for the TWAMP Modes field. This field is a recognized
extension mechanism for TWAMP.
6.1. Registry Specification
IANA created 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] and Section 3.1 of
[RFC5357], and extended by this memo. Modes are currently indicated
by setting single bits in the 32-bit Modes Field. However, more
complex encoding may be used in the future. Thus, this registry can
contain a total of 2^32 possible assignments.
6.2. Registry Management
Because the TWAMP Modes registry can contain a maximum of 2^32
values, and because TWAMP is an IETF protocol, this registry must be
updated only by "IETF Review" as specified in [RFC5226] (an RFC
documenting registry use that is approved by the IESG). For the
Morton & Hedayat Standards Track [Page 6]RFC 5618 TWAMP Extensions August 2009
TWAMP Modes registry, we expect that new features will be assigned
using monotonically increasing single bit positions and in the range
[0-31], unless there is a good reason to do otherwise (more complex
encoding than single bit positions may be used in the future, to
access the 2^32 value space).
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 RFC 5618
1 Unauthenticated RFC 4656, Section 3.1
2 Authenticated RFC 4656, Section 3.1
4 Encrypted RFC 4656, Section 3.1
8 Unauth. TEST protocol, RFC 5618, Section 3.1
Encrypted CONTROL
7. Acknowledgements
The authors would like to thank Len Ciavattone and Joel Jaeggli for
helpful review and comments.
8. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, September 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, October 2008.
Morton & Hedayat Standards Track [Page 7]RFC 5618 TWAMP Extensions August 2009
Authors' Addresses
Al Morton
AT&T Labs
200 Laurel Avenue South
Middletown, NJ 07748
USA
Phone: +1 732 420 1571
Fax: +1 732 368 1192
EMail: acmorton@att.com
URI: http://home.comcast.net/~acmacm/
Kaynam Hedayat
EXFO
285 Mill Road
Chelmsford, MA 01824
USA
Phone: +1 978 367 5611
Fax: +1 978 367 5700
EMail: kaynam.hedayat@exfo.com
URI: http://www.exfo.com/
Morton & Hedayat Standards Track [Page 8]
