Network Working Group B. Carpenter
Internet-Draft Univ. of Auckland
Intended status: Informational S. Jiang
Expires: March 16, 2018 B. Liu
Huawei Technologies Co., Ltd
September 12, 2017

Transferring Bulk Data over the GeneRic Autonomic Signaling Protocol (GRASP)


This document describes how bulk data may be transferred between Autonomic Service Agents via the GeneRic Autonomic Signaling Protocol (GRASP).

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Table of Contents

1. Introduction

The document [I-D.liu-anima-grasp-distribution] discusses how information may be distributed within the secure Autonomic Networking Infrastructure (ANI) [I-D.ietf-anima-reference-model]. Specifically, it describes using the Synchronization and Flood Synchronization mechanisms of the GeneRic Autonomic Signaling Protocol (GRASP) [I-D.ietf-anima-grasp] for this purpose. However, those mechanisms are limited to distributing GRASP Objective Options contained in messages that cannot exceed the GRASP maximum message size of 2048 bytes.

There are scenarios in autonomic networks where this restriction is a problem. One example is the distribution of network policy in lengthy formats such as YANG or JSON. Another case might be an Autonomic Service Agent (ASA) uploading a log file to the Network Operations Center (NOC). A third case might be a supervisory system downloading a software upgrade to an autonomic node.

Naturally, an existing solution such as a secure file transfer protocol or secure HTTP might be used for this. Other management protocols such as syslog [RFC5424] or NETCONF [RFC6241] might also be used for related purposes, or might be mapped directly over GRASP. The present document, however, applies to any scenario where it is preferable to re-use the autonomic networking infrastructure itself rather than an additional mechanism, but there is a need to transfer a large amount of data. The basic model is to use the GRASP Negotiation process to transfer and acknowledge multiple blocks of data in successive negotiation steps.

NOTE: This is an early draft of a solution. As the specification becomes more mature, the authors expect it to become precise enough to be placed on the standards track.

2. General Method for Bulk Transfer

As for any GRASP operation, the two participants are considered to be Autonomic Service Agents (ASAs) and they communicate using a specific GRASP Objective Option, containing its own name, some flag bits, a loop count, and a value. In bulk transfer, we can model the ASA acting as the source of the transfer as a download server, and the destination as a download client. Compared to a normal GRASP negotiation, the communication pattern is slightly asymmetric:

  1. The client first discovers the server by the GRASP discovery mechanism (M_DISCOVERY and M_RESPONSE messages).
  2. The client then sends a GRASP negotiation request (M_REQ_NEG message). The value of the objective expresses the requested item (e.g., a file name - see the next section for a detailed example).
  3. The server replies with a negotiation step (M_NEGOTIATE message). The value of the objective is the first section of the requested item (e.g., the first block of the requested file as a raw byte string).
  4. The client replies with a negotiation step (M_NEGOTIATE message). The value of the objective is a simple acknowledgement (e.g., the text string 'ACK').

The last two steps repeat until the transfer is complete. The server signals the end by transferring an empty byte string as the final value. In this case the client responds with a normal end to the negotiation (M_END message with an O_ACCEPT option).

Errors of any kind are handled with the normal GRASP mechanisms, in particular by an M_END message with an O_DECLINE option in either direction.

The block size must be chosen such that each step does not exceed the GRASP message size limit of 2048 bits.

This approach is safe since each block must be positively acknowledged, and data transfer errors will be detected by TCP. If a future variant of GRASP runs over UDP, the mandatory UDP checksum for IPv6 will detect such errors. The method does not currently specify retransmission for failed blocks, so a failed transfer will need to be restarted. In an enterprise network with low bit error rates, this is not considered a serious issue.

An observant reader will notice that the GRASP loop count mechanism, intended to terminate endless negotiations, will cause a problem for large transfers. For this reason, both the client and server must artificially increment the loop count by 1 before each negotiation step.

If network load is a concern, the data rate can be limited by inserting a delay before each negotiation step, with the GRASP timeout set accordingly. Either the server or the client, or both, could insert such a delay. Also, either side could use the GRASP Confirm Waiting (M_WAIT) message to slow the other side down.

The description above concerns bulk download from a server (responding ASA) to a client (requesting ASA). The data transfer could also be in the opposite (upload) direction with minor modifications to the procedure: the client would send the data blocks and the server would send acknowledgements.

3. Example for File Transfer

This example describes a client ASA requesting a file download from a server ASA.

Firstly we define a GRASP objective informally:

["411:mvFile", 3, 6, value]

The formal CDDL definition [I-D.ietf-cbor-cddl] is:

  mvfile-objective = ["411:mvFile", objective-flags, loop-count, value]
  objective-flags = ; as in the GRASP specification
  loop-count = ; as in the GRASP specification
  value = any

The objective-flags field is set to indicate negotiation.

Dry run mode must not be used.

The loop-count is set to a suitable value to limit the scope of discovery. A suggested default value is 6.

The value takes the following forms:

Note that the block size of 1024 is chosen to guarantee not only that each GRASP message is below the size limit, but also that only one TCP data packet will be needed, even on an IPv6 network with a minimum link MTU.

We now present outline pseudocode for the client and the server ASA. The API documented in [I-D.liu-anima-grasp-api] is used in a simplified way, and error handling is not shown in detail.

Pseudo code for client ASA (request and receive a file):

requested_obj = objective('411:mvFile')
locator = discover(requested_obj)
requested_obj.value = 'etc/test.pdf'
received_obj = request_negotiate(requested_obj, locator)
if error_code == declined:
    #no such file

file = open(requested_obj.value)
file.write(received_obj.value) #write to file
eof = False
while not eof:
    received_obj.value = 'ACK'
    received_obj.loop_count = received_obj.loop_count + 1
    received_obj = negotiate_step(received_obj)
    if received_obj.value == null:
        eof = True     
        file.write(received_obj.value) #write to file

#file received

Pseudo code for server ASA (await request and send a file):

supported_obj = objective('411:mvFile')
requested_obj = listen_negotiate(supported_obj)
file = open(requested_obj.value) #open the source file
if no such file:
    end_negotiate(False) #decline negotiation

eof = False
while not eof:
    chunk = #next block of file
    requested_obj.value = chunk
    requested_obj.loop_count = requested_obj.loop_count + 1
    requested_obj = negotiate_step(requested_obj)
    if chunk == null:
        eof = True
    if requested_obj.value != 'ACK':
        #unexpected reply...

4. Datagram Transport Layer

The above description and example assume that GRASP is implemented over a reliable transport layer such as TCP, such that lost or corrupted messages need not be considered. In the event that GRASP is implemented over an unreliable transport layer such as UDP, it would be necessary to add a block number to both the data block and acknowledgement objectives, so that missing blocks can be retransmitted, or duplicate blocks can be ignored. For example, the objective in Section 3 would become:

  mvfile-objective = ["411:mvFile", objective-flags, loop-count, value]
  objective-flags = ; as in the GRASP specification
  loop-count = ; as in the GRASP specification
  value = [block-number, any]
  block-number = uint

It would also be necessary for the transport layer to detect data errors, for example by enabling UDP checksums.

5. Maximum Transmission Unit

In an IPv6 environment, a minimal MTU of 1280 bytes can be assumed, and assuming that high throughput is not a requirement, bulk transfers can be designed to match that MTU. However, there are environments where the underlying physical MTU is much smaller. For example, on an IEEE 802.15.4 network it may be less than 100 bytes [RFC4944]. In such a case, a bulk transfer solution has several choices:

  1. Accept the overhead of an adaptation layer, and therefore assume a network-layer MTU of 1280 bytes.
  2. Attempt to determine the actual MTU available without lower-layer fragmentation.
  3. Attempt to determine a message size that provides optimum performance.

TBD: further discussion?

6. Other Considerations

TBD - discussion of specific use cases?

TBD - discussion of user space API for bulk transfer?

7. Security Considerations

All GRASP transactions are secured by the mandatory security substrate required by [I-D.ietf-anima-grasp]. No additional security issues are created by the application of GRASP described in this document.

8. IANA Considerations

This document makes no request of the IANA.

9. Acknowledgements


10. References

10.1. Normative References

[I-D.ietf-anima-grasp] Bormann, C., Carpenter, B. and B. Liu, "A Generic Autonomic Signaling Protocol (GRASP)", Internet-Draft draft-ietf-anima-grasp-15, July 2017.
[I-D.ietf-cbor-cddl] Birkholz, H., Vigano, C. and C. Bormann, "Concise data definition language (CDDL): a notational convention to express CBOR data structures", Internet-Draft draft-ietf-cbor-cddl-00, July 2017.

10.2. Informative References

[I-D.ietf-anima-reference-model] Behringer, M., Carpenter, B., Eckert, T., Ciavaglia, L., Pierre, P., Liu, B., Nobre, J. and J. Strassner, "A Reference Model for Autonomic Networking", Internet-Draft draft-ietf-anima-reference-model-04, July 2017.
[I-D.liu-anima-grasp-api] Carpenter, B., Liu, B., Wang, W. and X. Gong, "Generic Autonomic Signaling Protocol Application Program Interface (GRASP API)", Internet-Draft draft-liu-anima-grasp-api-04, June 2017.
[I-D.liu-anima-grasp-distribution] Liu, B. and S. Jiang, "Information Distribution over GRASP", Internet-Draft draft-liu-anima-grasp-distribution-04, May 2017.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J. and D. Culler, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007.
[RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, DOI 10.17487/RFC5424, March 2009.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011.

Appendix A. Change log [RFC Editor: Please remove]

draft-carpenter-anima-grasp-bulk-00, 2017-09-12:

Initial version.

Authors' Addresses

Brian Carpenter Department of Computer Science University of Auckland PB 92019 Auckland, 1142 New Zealand EMail:
Sheng Jiang Huawei Technologies Co., Ltd Q14, Huawei Campus, No.156 Beiqing Road Hai-Dian District, Beijing, 100095, P.R. China EMail:
Bing Liu Huawei Technologies Co., Ltd Q14, Huawei Campus No.156 Beiqing Road Hai-Dian District, Beijing, 100095 P.R. China EMail: