Internet DRAFT - draft-hsingh-ipv6-coin-ml
draft-hsingh-ipv6-coin-ml
COIN H. Singh
Internet-Draft MNK Consulting
Intended status: Standards Track December 9, 2019
Expires: June 11, 2020
New IPv6 Multicast Addresses for Switch ML
draft-hsingh-ipv6-coin-ml-03
Abstract
Recently, in-network aggregation to scale distributed machine
learning (ML) has been presented. A network switch implementation
uses IPv4 broadcast messages from switch to the hosts to send updates
to all workers. IPv6 does not support broadcast addresses. This
document proposes, IPv6 implementations use the IPv6 link-local all-
nodes multicast address, until a new IPv6 link-local multicast
address is assigned by IANA for switch to hosts multicast
communications.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 11, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Singh Expires June 11, 2020 [Page 1]
Internet-Draft IPv6 ML December 2019
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Additional Information . . . . . . . . . . . . . . . . . . . 2
4. P4 Considerations . . . . . . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 3
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
8.1. Normative References . . . . . . . . . . . . . . . . . . 4
8.2. Informative References . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4
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. Introduction
New computing in the network for ML uses IPv4 broadcast
communications between switch to hosts. [Switch-ML]. With IPv6,
multicast communications would be used. This document proposes a new
well-known multicast address be defined for such communications.
Until a new address is defined, the IPv6 link-local all-nodes
multicast address may be used. By definition, a layer-2 switch
operates in the link-local subnet. Thus, the IPv6 link-local
multicast address defined by this document suffices for switch to
host multicast communications.
3. Additional Information
It is common when new networking protocols such as RPL [RFC6550] and
Babel [RFC6126] were developed, each protocol requested IANA for a
new IPv6 link-local multicast address for use. Switch ML does not
have a protocol defined by IETF just yet and may never define one.
However, experiments in switch ML are already using IP or layer-2
broadcast communications. For IPv6, switch ML experiments should use
IPv6 link-local multicast communications. A new IPv6 link-local
multicast address for switch ML facilitates efficient filtering by
hosts.
Singh Expires June 11, 2020 [Page 2]
Internet-Draft IPv6 ML December 2019
If a switch is configured in layer-3 mode and if switch ML
communicates with hosts to another IPv6 subnet, an IPv6 Site-Local
Scope Multicast address is recommended for communications.
4. P4 Considerations
P4 issues arise when implementing the paper. A P4 header stack
(array) is used to represent the vector. P4 has no for loops, so how
does one add elements of the vector? There is the one way. You can
have one action that adds 1 header, another that adds 2, another that
adds 3, etc., and choose between them at run time via a table lookup.
Even with a vector with 20-50 elements, writing such P4 code manually
is risky. One has to write a Python script to generate such code.
The paper did not think of it, but an alternative exists. With every
element in the vector, use a new 1-byte field. The field has values
0 or 1. 1 represents bos (bottom of stack) like what MPLS uses. The
last element has bos set to 1. Then, one has a termination condition
in the P4 parser to terminate recursive parsing of vector. As the
parser is recursing through the vector, add the vector elements and
save sum in metadata. One does not use a bit for bos because the p4c
bmv2 model accepts a header on byte boundary.
The same p4c bmv2 model, also, does not accept an index into array if
the index is a run-time value. The p4-16 specification allows run-
time index. Algorithm 1 in the paper uses "p.idx" which is a run-
time value. Again, one has to use P4 tables. Include the run-time
variable index as a table search key, which selects between several
different actions that are identical, except for the constant array
index values they use. This gets cumbersome with 128 or 512 indices
in the paper. Again, one would have to generate P4 code to avoid
mistakes cut-and-pasting code. For 128 indices with some bit
shifting, maybe we reduces indices to 32. If an asic allows run-time
index into array, then it is better to use the asic simulator rather
than bmv2 simulator.
5. Security Considerations
Use IPSec [RFC4301].
6. IANA Considerations
This document requests IANA to assign a new IPv6 link-local multicast
address for use by network ML. This multicast address name is
Switch_ML_Host. An interface on the host MUST join this well-known
multicast address.
Additionally, IANA is requested to assign a new IPv6 Site-Local Scope
Multicast address for switch ML to host communication across IPv6
Singh Expires June 11, 2020 [Page 3]
Internet-Draft IPv6 ML December 2019
subnets. If configured to do so, an interface on the host MUST join
this well-known multicast address.
7. Acknowledgements
Thanks (in alphabetical order by first name) to Marco Canini for his
review.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC6126] Chroboczek, J., "The Babel Routing Protocol", RFC 6126,
DOI 10.17487/RFC6126, April 2011,
<https://www.rfc-editor.org/info/rfc6126>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>.
8.2. Informative References
[Switch-ML]
Sapio, A., Canini, M., Ho, C., Nelson, J., Kalnis, P.,
Kim, C., Krishnamurthy, A., Moshref, M., Ports, D. R., and
P. Richtarik, "SwitchML: Scaling Distributed Machine
Learning with In-Network Aggregation", February 2019,
<https://arxiv.org/pdf/1903.06701.pdf>.
Author's Address
Singh Expires June 11, 2020 [Page 4]
Internet-Draft IPv6 ML December 2019
Hemant Singh
MNK Consulting
7 Caldwell Drive
Westford, MA 01886
USA
Phone: +1 978 692 2340
Email: hemant@mnkcg.com
URI: http://mnkcg.com/
Singh Expires June 11, 2020 [Page 5]
