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The IETF has completed its work on the core specification of TWAMP - the Two-Way Active Measurement Protocol. This memo describes two closely-related features for TWAMP: an optional capability where the responder host returns some of the command octets or padding octets to the controller, and an optional sender packet format that ensures equal test packet sizes are used in both directions.
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].
This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79.
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Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.
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1.
Introduction
2.
Purpose and Scope
3.
TWAMP Control Extensions
3.1.
Connection Setup with New Features
3.2.
Reflect Octets: Request-TW-Session Packet Format
3.3.
Reflect Octets: Accept Session Packet Format
3.4.
Additional considerations
4.
Extended TWAMP Test
4.1.
Sender Behavior
4.1.1.
Packet Timings
4.1.2.
Reflect Octets: Packet Formats and Contents
4.1.3.
Reflect Octets: Interaction with Padding Truncation
4.1.4.
Symmetrical Size: Session-Sender Packet Format
4.1.5.
Symmetrical Size AND Reflect Octets: Session-Sender Packet Format
4.2.
Reflector Behavior
4.2.1.
Reflect Octets: Session-Reflector Packet Format and Contents
4.2.2.
Symmetrical Size: Session-Reflector Packet Format
4.2.3.
Symmetrical Size AND Reflect Octets: Session-Sender Packet Format
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
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The IETF has completed its work on the core specification of TWAMP - the Two-Way Active Measurement Protocol [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.). TWAMP is an extension of 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 that are designed to test implementations for protocol compliance.
This memo describes two closely-related features for TWAMP.
One is the OPTIONAL capability for the responder host to return a limited number of unassigned (padding) octets to the Control-Client or Session-Sender entities. With this capability, the Control-Client or Session-Sender can embed octets of information it deems useful and have the assurance that the corresponding reply/test packet will contain that information when it is reflected and returned (by the Server or Session-Reflector.
The memo also adds an OPTIONAL capability to assure that reflected test packets are the same size in both directions of transmission. This is accomplished by specifying a new TWAMP-Test Session-Sender packet format.
This memo and TWAMP is intended to be an update to [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.) when published. It is not required to implement the features described in this memo to claim compliance with [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.).
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The purpose of this memo is to define two OPTIONAL closely-related features for TWAMP [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.). The features enhance the TWAMP responder's capabilities to perform simple operations on control and test packets: the reflection of octets or padding and symmetrical sizes of fields in the TWAMP-Test packets. Motivations include permitting the controller host to tag packets with an index for simplified identification, and/or assert that the same size test packets will be used in each direction.
The scope of the memo is currently limited to specifications of the following features:
Extension of the modes of operation through assignment of two 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.) for the format of the Server Greeting message), while retaining backward compatibility with the core TWAMP [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.) implementations. The two new values correspond to the two features defined in this memo.
When the Server and Control-Client have agreed to use the Reflect Octets 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 that mode, as identified below.
When the Server and Control-Client have agreed to use the Symmetrical Size 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 that mode, as identified below.
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TWAMP-Control protocol [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.) uses the Modes Field to identify and select specific communication capabilities, and this field is a recognized extension mechanism. The following sections describe two such extensions.
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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.) and section 3.1 of [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.). The new features require two new bit positions (and values) to identify the ability of the Server/Session-Reflector to reflect specific octets back to the Control-Client/Session-Sender, and to support the new Session-Sender packet format in TWAMP-Test Protocol. With this added feature, the complete set of TWAMP Modes Field bit positions and 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, RFC5681, Section 3.1
Encrypted CONTROL
zzz Individual Session RFC????, Section 3.1
Control
--------------------------------------------------------
xxx Reflect Octets new bit position (X)
Capability
yyy Symmetrical Size new bit position (Y)
Sender Test Packet Format
In the original OWAMP Modes 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 [RFC5618] (Morton, A. and K. Hedayat, “Mixed Security Mode for the Two-Way Active Measurement Protocol (TWAMP),” August 2009.), bit position 3 allows unauthenticated TWAMP Test protocol to be used with encryption on the TWAMP-Control protocol in a mixed mode of operation.
The Server sets one or both of the new bit positions (X and Y) in the Modes Field of the Server Greeting message to indicate its capabilities and willingness to operate in either of these modes (or both) if desired.
>>>IANA: change xxx, yyy, X, and Y to the assigned values <<<
If the Control-Client intends to operate all test sessions invoked with this control connection using one or both of the new modes, it MUST set the Modes Field bit corresponding to that function in the Setup Response message.
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The bits designated for the Reflect Octets 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 (66 octets) not shown ... . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Padding Length (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Start Time, (8 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Timeout, (8 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type-P Descriptor | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octets to be reflected | Length of padding to reflect | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | HMAC (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The "Padding Length" Field *continues* to specify the number of padding octets that the Session-Sender will append to ALL TWAMP-Test packets associated with this test session. See below for considerations on the minimum length of the padding octets, following the definitions of the two new fields that follow the Type-P Descriptor.
Note that the number of padding octets appended to the Session-Reflector's test packet depends on support for the RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.).
The "Octets to be reflected" Field SHALL be 2 octets long, as shown and contains the octets that the Server MUST reflect in the Accept Session message as specified below.
The "Length of padding to reflect" Field SHALL be 2 octets long, and contain an unsigned binary value in units of octets. This field communicates the length of the padding in the TWAMP-Test Packet that the Session-Sender expects to be reflected, and the length of octets that the Session-Reflector SHALL return in include in its TWAMP-Test packet format (see section 4.2). By including this length field in the Request-TW-Session message, a Server is able to determine if it can comply with a specific request to reflect padding in the TWAMP-Test packets, and to arrange for the Session-Reflector processing in advance.
The "Padding Length" SHOULD be >= 27 octets when specifying a test session using the Unauthenticated TWAMP-Test mode, to allow for the RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.).
The "Padding Length" SHOULD be >= 56 octets when specifying a test session using the Authenticated or Encrypted TWAMP-Test modes, to allow for the RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.).
The "Padding Length" SHALL be > the "Length of padding to reflect" when specifying a test session using the OPTIONAL Reflect Octets mode.
The "Padding Length" SHALL be >= 27 + "Length of padding to reflect" octets when specifying a test session using BOTH the OPTIONAL Reflect Octets mode and the RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.).
The "Padding Length" SHALL be >= 56 + "Length of padding to reflect" octets when specifying a test session using BOTH the OPTIONAL Reflect Octets mode and the RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.).
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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) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reflected octets | Server octets | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ (8 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | HMAC (16 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The "Reflected octets" field SHALL contain the octets from the Request-TW-Session "Octets to be reflected" Field, and be 2 octets long, as shown.
The "Server octets" field SHALL contain information that the Server intends to be returned in the TWAMP-Test packet padding to-be-reflected Field, OR SHALL be zero, and be 2 octets long, as shown. Although the Server determines the SID, this field is very long (16 octets) and does not normally appear in TWAMP-Test packets.
When supporting the RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.), IF calculations on the Padding lengths reveal that there are insufficient octets supplied to produce equal-length Session-Sender and Session-Reflector test packets, then the Accept Field MUST be set to 3 = some aspect of the request is not supported.
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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.
With the publication of this memo as an RFC, the last 7 bit positions of the Modes 32-bit Field are used. A Control-Client conforming to this extension of [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.) MAY ignore the values in the higher bits of the Modes Field, or it MAY support other features that are communicated in those bit positions. The other bits are available for future protocol extensions.
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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 section 4[RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.) defines two additional test packet formats for packets transmitted by the Session-Reflector. The appropriate format depends on the security mode chosen. The new modes specified here utilize some of the padding octets within each test packet format, or require truncation of those octets depending on the security mode in use.
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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 [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.)).
The Reflect octets mode re-designates the original TWAMP-Test (and OWAMP-Test) Packet Padding Field (see 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 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 | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | | Packet Padding (to be reflected) | . (length in octets specified in command) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . Additional Packet Padding . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The "Packet Padding (to be reflected)" Field SHALL correspond to the length of octets specified in the Request-TW-Session "Length of padding to reflect" Field to this test session. These are the octets that the Session-Sender expects will be returned by the Session-Reflector.
The length of the "Additional Packet Padding" Field is the difference between two fields in the Request-TW-Session command, as follows:
"Additional Packet Padding", in octets =
"Padding Length" - "Length of padding to reflect"
One possible use of the first 4 octets of the "Packet Padding (to be reflected)" Field is shown 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Server octets |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Client octets | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| Packet Padding (to be reflected) |
. (length in octets specified elsewhere) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+In this example, the "Client octets" and the "Server octets" fields contain the same information that the Client and Server exchanged in the Request-TW-Session and Accept-Session messages corresponding to this specific test session. These octets would be reflected the same as the rest of the "Packet Padding (to be reflected)" Field.
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When the Reflect Octets mode is selected, and the RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.) is supported, the Session-Sender MUST anticipate a minimum padding required to achieve equal size test packets in both directions. The amount of padding needed to achieve symmetrical packet size depends on BOTH the security mode (Unauthenticated/Authenticated/Encrypted) and whether the Reflect Octets mode is selected simultaneously.
When using the RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.) alone, the Session-Sender MUST append sufficient Packet Padding octets to allow the same IP packet payload lengths to be used in each direction of transmission (this is usually desirable). To compensate for the Session-Reflector’s larger test packet format, the Session-Sender MUST append at least 27 octets of padding in Unauthenticated mode, and at least 56 octets in Authenticated and Encrypted modes. The sizes of TWAMP Test protocol packets and the resulting truncated padding to achieve equal packet sizes in both directions are shown in the table below:
| Octets in: | Unauthenticated Mode | Auth/Encrypted Mode |
|---|---|---|
| Reflector Header | 41 | 104 |
| Sender Header | 14 | 48 |
| Truncated Padding | 27 | 56 |
| TWAMP-Test Padding Trucation |
When using the Reflect Octets mode simultaneously with the RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.), the Session-Sender MUST append at least 27 octets of padding plus the "Length of the padding to reflect" octets when operating in Unauthenticated mode. The Session-Sender MUST append at least 56 octets of padding plus the "Length of the padding to reflect" octets when operating in Authenticated and Encrypted modes.
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When the Symmetrical Size mode is selected, the Session-Sender SHALL use the following TWAMP-Test Packet Format in Unauthenticated mode:
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 (27 octets) | | | | | | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+ + . . . Packet Padding . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This feature REQUIRES only a new Session-Sender test packet format, the Session-Reflector test packet format is unchanged.
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When BOTH the Symmetrical Size mode and the Reflect Octets mode are selected, the Session-Sender SHALL use the following TWAMP-Test Packet Format in Unauthenticated mode:
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 (27 octets) | | | | | | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+ + | Packet Padding (to be reflected) | . (length in octets specified in command) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . Additional Packet Padding . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In this combined mode, the Packet Padding to be reflected follows the 27 MBZ octets. In Authenticated or Encrypted modes, the Packet Padding to be reflected follows the 56 MBZ octets.
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The TWAMP Reflector follows the procedures and guidelines in section 4.2 of [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.), with the following additional functions:
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The Reflect Padding feature re-designates the packet padding field, as shown below. When the Reflect Octets mode is selected, the Session-Sender SHALL use the following TWAMP-Test Packet Format in 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 | Packet Padding (from Session-Sender) | +-+-+-+-+-+-+-+-+ + . . + +-+-+-+-+-+-+-+-+ | Packet Padding (from Session-Sender) | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | | | . Additional Packet Padding . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The "Packet Padding (from Session-Sender)" field MUST be the same octets as the "Packet Padding (to be reflected)" field in the Session-Sender's test packet, and therefore MUST conform to the length specified in the Request-TW-Session message.
When simultaneously using the RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.) AND Reflect octets mode, the Session-Reflector MUST reflect the designated octets from the Session-Sender's test packet in the "Packet Padding (from Session-Sender)" Field, and MAY re-use additional Packet Padding from the Session-Sender. The Session-Reflector MUST truncate the padding such that the highest number octets are discarded, and the test packet length equals the Session-Sender's packet length. When using the RECOMMENDED truncation process, the Session-Reflector MUST truncate exactly 27 octets of padding in Unauthenticated mode, and exactly 56 octets in Authenticated and Encrypted modes.
The Session-Reflector MAY re-use the Sender’s Packet Padding (since the requirements for padding generation are the same for each).
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When Symmetrical Size mode is selected, the Session-Sender packet formats for unauthenticated and authenticated/encrypted modes are identical to the core TWAMP specification, section 4.2.1 of [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.). Thus, the Session-Reflector test packet format is unchanged.
The Session-Reflector MUST construct its test packet using the information in the Session-Sender's test packet. The length of the Session-Reflector's test packet SHALL equal the length of the Session-Sender's test packet.
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When BOTH the Symmetrical Size mode and the Reflect Octets mode are selected, the Session-Reflector MUST operate using the Session_Reflector Packet Format defined in section 4.1.5, where the Padding Octets are separated from the information fields, and the Padding to be Reflected field precedes the Additional Padding.
The Session-Reflector SHALL use the same TWAMP-Test Packet Format as specified in section 4.2.1 above.
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These extended modes of operation do not appear to permit any new attacks on hosts communicating with core TWAMP [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.).
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 [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 2008.).
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This memo adds two modes to the IANA registry for the TWAMP Modes 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 [RFC5618] (Morton, A. and K. Hedayat, “Mixed Security Mode for the Two-Way Active Measurement Protocol (TWAMP),” August 2009.)). TWAMP-Modes are specified in TWAMP Server Greeting messages and Set-up Response messages, as described in section 3.1 of [RFC5357] (Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” October 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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This registry must be updated only by "IETF Consensus" as specified in [RFC5226] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.)(an RFC documenting registry use that is approved by the IESG).
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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, RFC5618, Section 3.1 (3)
Auth. CONTROL
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xxx Reflect Octets this memo, section 3.1
Capability new bit position (X)
yyy Symmetrical Size this memo, section 3.1
Sender Test Packet Format new bit position (Y)
The suggested values are
X=5, xxx=32
Y=6, yyy=64
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The authors would like to thank Walt Steverson and Stina Ross for helpful review and comments.
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| [RFC2119] | Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (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). |
| [RFC5226] | Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” BCP 26, RFC 5226, May 2008 (TXT). |
| [RFC5357] | Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, “A Two-Way Active Measurement Protocol (TWAMP),” RFC 5357, October 2008 (TXT). |
| [RFC5618] | Morton, A. and K. Hedayat, “Mixed Security Mode for the Two-Way Active Measurement Protocol (TWAMP),” RFC 5618, August 2009 (TXT). |
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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: |