Internet DRAFT - draft-bormann-loops-geneve-binding
draft-bormann-loops-geneve-binding
loops C. Bormann
Internet-Draft Universitaet Bremen TZI
Intended status: Standards Track 12 June 2020
Expires: 14 December 2020
Embedding LOOPS in Geneve
draft-bormann-loops-geneve-binding-01
Abstract
LOOPS (Local Optimizations on Path Segments) aims to provide local
in-network loss recovery. It can be used with tunneling protocols to
efficiently recover lost packets on a single segment of an end-to-end
path instead of leaving recovery to the end-to-end protocol,
traversing the entire path.
[I-D.welzl-loops-gen-info] defines the information to be carried
between LOOPS ingress and egress nodes in a generic way, giving a
guideline on defining the common elements to embed LOOPS functions in
various tunnel protocols. The present document specifies how to
embed LOOPS in the overlay tunnel protocol chosen for the initial
LOOPS specification, Geneve [I-D.ietf-nvo3-geneve].
Status of This Memo
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This Internet-Draft will expire on 14 December 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Geneve LOOPS Frame Format . . . . . . . . . . . . . . . . . . 3
3.1. Flags and Flag Based Data . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1. Geneve Option Class . . . . . . . . . . . . . . . . . . . 6
5.2. LOOPS Geneve Type Numbers . . . . . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
LOOPS (Local Optimizations on Path Segments) aims to provide local
in-network loss recovery. The LOOPS problems and opportunities draft
[I-D.li-tsvwg-loops-problem-opportunities] illustrates some typical
scenarios where LOOPS are applicable. One way to use LOOPS is to map
it onto a tunnel protocol. The path segment on which LOOPS is
applied then is a tunnel, which can be an existing one or created on
purpose.
LOOPS allows the packet loss recovery to be performed over specific
segments instead of end-to-end, enabling faster and more reliable
data delivery. [I-D.welzl-loops-gen-info] defines the information to
be carried between LOOPS ingress and egress nodes in a generic way,
giving a guideline on defining the common elements to embed LOOPS
functions in various tunnel protocols.
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Geneve [I-D.ietf-nvo3-geneve] is an encapsulation protocol that can
be used to create overlay tunnels. It defines an extensible TLV
structure to carry so-called "tunnel options". The present document
employs this flexibility, specifying how to embed LOOPS in Geneve.
This specification covers the format and Geneve-specific procedures
only: the actual LOOPS function and procedures are defined in
[I-D.welzl-loops-gen-info].
LOOPS has two modes of loss recovery, retransmission and forward
error correction (FEC). The current version of the present document
covers retransmission only.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document makes use of the terminology defined in
[I-D.welzl-loops-gen-info].
3. Geneve LOOPS Frame Format
Figure 1 shows the format of the Geneve Header and a single Geneve
Option, as defined in [I-D.ietf-nvo3-geneve]. Geneve LOOPS defines a
new Option class called LOOPS to carry LOOPS forward and backward
information.
Geneve Header and Option:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver| Opt Len |O|C| Rsvd. | Protocol Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Virtual Network Identifier (VNI) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Variable Length Options |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Class | Type |R|R|R| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Variable Option Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 1: Geneve Header and Option Format
In the Geneve Option structure, a Geneve LOOPS option uses the
following values:
* Option Class: TBD1 for LOOPS (see Section 5).
* Type: Based on the substructure already defined in Geneve, which
uses bit 0 (the most significant bit) to indicate a critical
option (see see Figure 2), LOOPS defines two type numbers: 0 for
LOOPS retransmission mode, and 64 for FEC mode. The present
document only addresses messages with LType=0.
TBD: Additional type numbers could be defined, possibly obviating the
need for some of the flags in the current option structure.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|C| LType |
+-+-+-+-+-+-+-+-+
Figure 2: Type Field Format in Geneve LOOPS Option
* C: Critical bit as defined in [I-D.ietf-nvo3-geneve].
* LType: LOOPS Mode.
- 0: Retransmission mode. In this mode, the LOOPS option format
and operations follow this document.
- 64: FEC mode
- Further mode values can be assigned in an IANA registry (see
Section 5.2).
* Length: Length of Variable Option Data field, expressed in four
byte multiples excluding the option header, ranging from 0 to 31.
As the option header is another four bytes, the total length of
the option in bytes is therefore 4 * (1 + Length), yielding a
maximum total length of 128 bytes.
* Variable option data: consists of two parts, Flags and Flag Based
Data, as shown in Figure 3.
- Flags: 16 bits, as described in next subsection. Some of the
flags indicate the presence of additional data in the field of
Flag Based Data.
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- Flag Based Data: This field consists of one or multiple
optional data blocks whose presence is indicated by the
corresponding flag bits. Any remaining bytes needed to reach a
multiple of four bytes are filled with zeroes.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
~ Flag Based Data ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Variable Option Data Format in Geneve LOOPS Option
3.1. Flags and Flag Based Data
Flags for LOOPS Tunnel Options are defined in Figure 4. Some flags
cause additional data blocks to occur in the Flags Based Data field.
Those additional data blocks are placed in the order of the flags
causing them.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|I|R|D|S|T|E|A|R| |B|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Flags in Variable Option Data in Geneve LOOPS Option
A number of the flag bits are used on their own and do not cause
carrying additional data:
* I: Initial Packet Sequence Number (PSN) flag; may be set by the
LOOPS ingress to notify the egress about using a new initial PSN.
* R: Initial PSN Received flag; echo of I flag provided by the LOOPS
egress.
* D: ACK Desired flag; set by the LOOPS ingress if it wants the
egress to generate an acknowledgement immediately upon receiving a
particular packet.
These flag bits cause the addition of a single 32-bit number each:
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* S: PSN flag; indicates a PSN data block is carried in the Flag
Based Data field. It must be set when a packet payload is
present. It must not be set if the packet is a pure LOOPS ACK
packet, i.e. when no payload is included in the packet.
* T: Timestamp flag. When set, it indicates a Timestamp data block
is carried in the Flag Based Data field.
// TBD: Might want to have "timestamp" and "echo" fields of less
or
// more than 4 bytes.
* E: Echoed Timestamp flag. When set, it indicates an Echoed
Timestamp data block is carried in the Flag Based Data field.
* A: ACK number flag. When set, it indicates the presence of a
Block 1 ACK information block.
* R: Reception time flag: May only be set if A is set. Indicates
that an absolute reception time is given (Format TBD).
Finally, a single flag bit is defined that causes the addition of a
variable-length block (therefore this flag is put as the least
significant bit of Flags):
* B: Block 2 flag. When set, it indicates the presence a Block 2
ACK information block, with the following format: TBD
// copy over the structure we have in gen-info.
Acknowledgement information can be sent as a pure ACK packet without
payload or piggybacked in a data packet.
4. Security Considerations
The security considerations of [I-D.welzl-loops-gen-info] and
[I-D.ietf-nvo3-geneve] apply.
5. IANA Considerations
5.1. Geneve Option Class
IANA is requested to assign a new option class for LOOPS from the
"Geneve Option Class" registry.
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+--------------+-----------------------------+
| Option Class | Description |
+==============+=============================+
| TBD1 | LOOPS (Local Optimizations |
| | on Path Segments) [RFCthis] |
+--------------+-----------------------------+
Table 1
5.2. LOOPS Geneve Type Numbers
IANA is requested to create a registry for type numbers ("LType") as
used in the TBD1 option class for LOOPS from the "Geneve Option
Class" registry, with the following three columns:
Type Number: Integer between 0 and 127
Description: Short Description
Reference: Reference to Specification
The initial contents of the registry is:
+-------------+---------------------+-----------+
| Type Number | Description | Reference |
+=============+=====================+===========+
| 0 | Retransmission mode | [RFCthis] |
+-------------+---------------------+-----------+
| 64 | FEC mode | [RFCthis] |
+-------------+---------------------+-----------+
Table 2
(Registry policy TBD, probably Specification Required.)
6. References
6.1. Normative References
[I-D.welzl-loops-gen-info]
Welzl, M. and C. Bormann, "LOOPS Generic Information Set",
Work in Progress, Internet-Draft, draft-welzl-loops-gen-
info-03, 9 March 2020, <http://www.ietf.org/internet-
drafts/draft-welzl-loops-gen-info-03.txt>.
[I-D.ietf-nvo3-geneve]
Gross, J., Ganga, I., and T. Sridhar, "Geneve: Generic
Network Virtualization Encapsulation", Work in Progress,
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Internet-Draft, draft-ietf-nvo3-geneve-16, 7 March 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-nvo3-
geneve-16.txt>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
6.2. Informative References
[I-D.li-tsvwg-loops-problem-opportunities]
Yizhou, L., Zhou, X., Boucadair, M., and J. Wang, "LOOPS
(Localized Optimizations on Path Segments) Problem
Statement and Opportunities for Network-Assisted
Performance Enhancement", Work in Progress, Internet-
Draft, draft-li-tsvwg-loops-problem-opportunities-04, 6
January 2020, <http://www.ietf.org/internet-drafts/draft-
li-tsvwg-loops-problem-opportunities-04.txt>.
Acknowledgements
Sami Boutros provided some advice on the use of Geneve in this
protocol binding.
Author's Address
Carsten Bormann
Universitaet Bremen TZI
Postfach 330440
Bremen D-28359
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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