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The IETF is completing its work on TWAMP - the Two-Way Active Measurement Protocol. This memo describes a proposed feature for TWAMP, intended for discussion in the IP Performance Metrics WG. The feature gives the reflector the ability to return some of the packet padding bits to the sender.
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].
1.
Introduction
2.
Purpose and Scope
3.
TWAMP Control Extensions
3.1.
Connection Setup with Reflect Padding Feature
3.2.
Request-TW-Session Packet Format
3.3.
Accept Session Packet Format
3.4.
Additional considerations
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.
Registry Contents
7.
Acknowledgements
8.
References
8.1.
Normative References
8.2.
Informative References
§
Authors' Addresses
§
Intellectual Property and Copyright Statements
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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.).
This memo describes a new proposed feature for TWAMP, so it can be discussed and interest to take-up the feature assessed. This feature adds the capability for the Session-Reflector to return a limited number of unassigned (padding) bits to the Server/Session-Sender. With this capability, the Control-Client/Session-Sender can information it deems useful and have the assurance that the corresponding test packet will contain the information when it is returned.
The relationship between this memo and TWAMP is intended to be an update to the TWAMP RFC when published.
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The purpose of this memo is to describe an additional function and feature for TWAMP [I‑D.ietf‑ippm‑twamp] (Babiarz, J., “A Two-way Active Measurement Protocol (TWAMP),” August 2008.). The feature needs a clear description so it can be discussed and (hopefully) adopted in the IP Performance Metrics Charter.
The scope of the memo is currently limited to specifications of the following feature:
(other items may be added)
When new features are discussed and reach consensus, they may become chartered work items in IETF IPPM (and may appear in a different memo).
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TWAMP-Control protocol is a derivative of the OWAMP-Control protocol, and provides two-way measurement capability. TWAMP [I‑D.ietf‑ippm‑twamp] (Babiarz, J., “A Two-way Active Measurement Protocol (TWAMP),” August 2008.) uses the Mode field to identify and select specific communication capabilities, and this field is a recognized extension mechanism. The following sections describe one such extension.
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TWAMP connection establishment follows the 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 Reflect Padding feature requires two new bit positions (and values) to identify the ability of the Server/Session-Reflector to reflect specific octets of Packet Padding back to the Client/Sender. With this added feature, the complete set of TWAMP mode values would be 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, draft-...-more-twamp (3)
Auth. CONTROL
16 Unauth. TEST protocol, draft-...-more-twamp (4)
Encrypted CONTROL
32 Auth. TEST protocol, draft-...-more-twamp (5)
Encrypted CONTROL
--------------------------------------------------------
xx Reflect Padding new bit position (X)
Capability
yyy Reflect & Operate new bit position (Y)
on Padding Bits
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 the [I‑D.morton‑ippm‑more‑twamp] (Morton, A. and K. Hedayat, “More Features for TWAMP,” July 2008.) bit positions (3, 4 or 5) discontinue the inheritance of the security mode in the Test protocol.
The Server sets one or both of the new bit positions (possibly 6 and/or 7) in the Server Greeting message to indicate its capabilities and willingness to operate in these modes if desired.
If the Control-Client intends to operate all test sessions under this control connection using one of the new modes, it MUST set one of mode bits corresponding to that mode in the Setup Response message.
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The bits designated for the Reflect Padding feature in the Request-TW-Session command are as shown in the packet format below.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 5 | MBZ | IPVN | Conf-Sender | Conf-Receiver | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Number of Schedule Slots | . . ... Many fields not shown ... . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type-P Descriptor | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Padding (to be reflected) | MBZ (2 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | HMAC (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The "Packet Padding (to be reflected)" field SHALL be 2 octets long, as shown.
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The bits designated for the Reflect Padding feature in the Accept Session command are as shown in the packet format below.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Accept | MBZ | Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | | | SID (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Padding (to be reflected) | MBZ (2 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ (8 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | HMAC (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The "Packet Padding (to be reflected)" field SHALL be 2 octets long, as shown.
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The value of the Modes field sent by the Server (in the Server Greeting message) is the bit-wise OR of the mode values that it is willing to support during this session.
If BOTH the above modes are adopted, the last eight bits of the Modes 32-bit field are used. The first 24 bits MUST be zero. A client conforming to this version of the specification MUST ignore the values in the first 24 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.).
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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.) section 4 defines two additional test packet formats for packets transmitted by the Session-Reflector. The appropriate format depends on the security mode chosen. This feature utilizes some of the bits within each test packet format.
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This section describes extensions to the behavior of the TWAMP Session-Sender.
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The Send Schedule is not utilized in TWAMP, and this is unchanged in this memo.
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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.) (as indicated in section 4.1.2 of TWAMP [I‑D.ietf‑ippm‑twamp] (Babiarz, J., “A Two-way Active Measurement Protocol (TWAMP),” August 2008.)).
The Reflect Padding feature re-designates the packet padding field, as shown below for unauthenticated mode:
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Timestamp | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Estimate | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ | Length (2 oct) | Ext ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Packet Padding (to be reflected) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Additional Packet Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The "Packet Padding (to be reflected)" field MAY be as long as 12 octets, as shown. IF the test packet length is truncated within this field, THEN ALL packet padding MUST be reflected by Session-Reflectors using this feature.
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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 additional functions:
The Reflect Padding feature re-designates the packet padding field, as shown below for unauthenticated mode:
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Timestamp | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Estimate | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Receive Timestamp | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender Timestamp | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender Error Estimate | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender TTL | Length (2 oct) | Ext ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Packet Padding (from Session-Sender) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Additional Packet Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The "Packet Padding (to be reflected)" field MAY be as long as 12 octets, as shown. IF the test packet length is truncated within this field, THEN ALL packet padding MUST be reflected by Session-Reflectors using this feature.
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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.).
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This memo adds two mode combinations to the IANA registry for the TWAMP Mode field, and describes behavior when the new modes are used. This field is a recognized extension mechanism for TWAMP.
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IANA has created a TWAMP-Modes registry (as requested in [I‑D.morton‑ippm‑more‑twamp] (Morton, A. and K. Hedayat, “More Features for TWAMP,” July 2008.)). TWAMP-Modes are specified in TWAMP Server Greeting messages and Set-up Response messages, as described in section 3.1 of [I‑D.ietf‑ippm‑twamp] (Babiarz, J., “A Two-way Active Measurement Protocol (TWAMP),” August 2008.), 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.
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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.
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No experimental values are currently assigned for the Modes Registry.
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TWAMP Modes Registry is recommended to be augmented as follows:
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, draft-...-more-twamp (3)
Auth. CONTROL
16 Unauth. TEST protocol, draft-...-more-twamp (4)
Encrypted CONTROL
32 Auth. TEST protocol, draft-...-more-twamp (5)
Encrypted CONTROL
--------------------------------------------------------
xx Reflect Padding this memo, section 3.1
Capability new bit position (X)
yyy Reflect & Operate this memo, section 3.1
on Padding Bits new bit position (Y)
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The authors would like to thank future readers for helpful review and comments.
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| [I-D.ietf-ippm-twamp] | Babiarz, J., “A Two-way Active Measurement Protocol (TWAMP),” draft-ietf-ippm-twamp-09 (work in progress), August 2008 (TXT). |
| [I-D.morton-ippm-more-twamp] | Morton, A. and K. Hedayat, “More Features for TWAMP,” draft-morton-ippm-more-twamp-02 (work in progress), July 2008 (TXT). |
| [RFC2119] | Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML). |
| [RFC2434] | Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” BCP 26, RFC 2434, October 1998 (TXT, HTML, XML). |
| [RFC4656] | Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M. Zekauskas, “A One-way Active Measurement Protocol (OWAMP),” RFC 4656, September 2006 (TXT). |
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| [x] | “.” |
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| 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/ |
| Len Ciavattone | |
| AT&T Labs | |
| 200 Laurel Avenue South | |
| Middletown,, NJ 07748 | |
| USA | |
| Phone: | +1 732 420 1239 |
| Fax: | |
| Email: | lencia@att.com |
| URI: |
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