Network Working Group S. Venaas
Internet-Draft Cisco Systems, Inc.
Updates: 3973, 5015, 6754, 7761, ietf- A. Retana
pim-source-discovery-bsr (if Huawei R&D USA
approved) March 1, 2018
Intended status: Standards Track
Expires: September 2, 2018
PIM reserved bits and type space extension
draft-venaas-pim-reserved-bits-00
Abstract
The currently defined PIM version 2 messages share a common message
header format. The common header definition contains eight reserved
bits. This document specifies how these bits may be used by
individual message types, and creates a registry containing the per
message type usage. This document also extends the PIM type space by
defining a new message type where four of the flag bits are used as
an extended type range.
This document Updates RFC7761 and RFC3973 by defining the use of the
currently Reserved field in the PIM common header. This document
further updates RFC7761 and RFC3973, along with RFC5015, RFC6754 and
I-D.ietf-pim-source-discovery-bsr, by specifying the use of the
currently Reserved bits for each PIM message.
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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 2, 2018.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
3. PIM header common format . . . . . . . . . . . . . . . . . . 3
4. Flag Bit definitions . . . . . . . . . . . . . . . . . . . . 3
4.1. Flag Bits for Type 4 (Bootstrap) . . . . . . . . . . . . 4
4.2. Flag Bits for Type 10 (DF Election) . . . . . . . . . . . 4
4.3. Flag Bits for Type 12 (PFM) . . . . . . . . . . . . . . . 4
4.4. Flag Bits for Type 15 (Type Space Extension) . . . . . . 4
5. PIM Type Space Extension . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
The currently defined PIM version 2 messages share a common message
header format defined in the PIM Sparse Mode [RFC7761] and Dense Mode
[RFC3973] specifications. The common header definition contains
eight reserved bits. The message types defined in these documents
all use this common header. However, several messages already make
use of one or more bits, including the Bootstrap [RFC5059], DF-
Election [RFC5015], and PIM Flooding Mechanism (PFM)
[I-D.ietf-pim-source-discovery-bsr] messages. There is no document
formally specifying that these bits are to be used per message type.
This document refers to the bits specified as Reserved in the common
PIM header [RFC7761] [RFC3973] as PIM message type flag bits, or
simply flag bits, and it specifies that they are to be separately
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used on a per message type basis. It creates a registry containing
the the per message type usage. For a particular message type, the
usage of the flag bits can be defined in the document defining the
message type, or a new document that updates that document.
The PIM message types as defined in the PIM Sparse Mode [RFC7761] and
Dense Mode [RFC3973] specifications are in the range from 0 to 15.
That type space is almost exhausted. Message type 15 was reserved by
[RFC6166] for type space extension. In Section 5, this document
specifies the use of the flag bits for Type 15 in order to extend the
PIM type space. The registration procedure for the extended type
space is the same as for the existing type space, and the existing
PIM message type registry is updated to include the extended type
space.
2. Conventions used in this document
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.
3. PIM header common format
The common PIM header is defined in section 4.9 of [RFC7761] and
section 4.7.1 of [RFC3973]. This document updates the definition of
the Reserved field and refers to that field as PIM message type flag
bits, or simply flag bits. The new common header format is as 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Flags Bits | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Flags Bits field is defined in Section 4. All other fields
remain unchanged.
4. Flag Bit definitions
Unless otherwise specified, all the flag bits for each PIM type are
Reserved [RFC8126]. They MUST be set to zero on transmission, and
they MUST be ignored upon receipt. The specification of a new PIM
type, MUST indicate whether the bits should be treated differently.
Currently for the message types 0 (Hello), 1 (Register), 2 (Register
Stop), 3 (Join/Prune), 5 (Assert), 6 (Graft), 7 (Graft-Ack), 8
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(Candidate RP Advertisement), 9 (State Refresh) and 11 (ECMP
Redirect), all flag bits are Reserved.
When defining flag bits it is helpful to have a well defined way of
referring to a particular bit. The most significant of the flag
bits, the bit immediately following the type field is referred to as
bit 7. The least significant, the bit right in front of the checksum
field is referred to as bit 0. This is shown in the diagram 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type |7 6 5 4 3 2 1 0| Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.1. Flag Bits for Type 4 (Bootstrap)
PIM message type 4 (Bootstrap) [RFC5059] defines flag bit 7 as No-
Forward. The usage of the bit is defined in that document. The
remaining flag bits are Reserved.
4.2. Flag Bits for Type 10 (DF Election)
PIM message type 10 (DF Election) [RFC5015] specifies that the four
most significant flag bits (bits 4-7) are to be used as a sub-type.
The remaining flag bits are currently Reserved.
4.3. Flag Bits for Type 12 (PFM)
PIM message type 12 (PFM) [I-D.ietf-pim-source-discovery-bsr] defines
flag bit 7 as No-Forward. The usage of the bit is defined in that
document. The remaining flag bits are Reserved.
4.4. Flag Bits for Type 15 (Type Space Extension)
This type and the flag bit usage is defined in Section 5.
5. PIM Type Space Extension
The type space defined by the existing PIM specifications is almost
exhausted. This document defines type 15 (Type Space Extension)
allowing for 16 additional types by using the four most significant
flag bits (bits 4-7) as a new field to store the extended type.
These types are referred to as types 15.0 to 15.15 where the last
number denotes the value stored in the new field. The remaining four
flag bits (bits 0-3) are Reserved to be used by each extended type.
The specification of a new PIM extended type MUST indicate whether
the bits should be treated differently. The common header for types
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15.0 to 15.15 is shown in the diagram below. The extended type field
"Rsvd" denotes the value after the dot.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver|Type 15|SubType| Rsvd | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6. Security Considerations
This document clarifies the use of the flag bits in the common PIM
header and it extends the PIM type space. As such, there is no
impact on security or changes to the considerations in [RFC7761] and
[RFC3973].
7. IANA considerations
This document updates the PIM Message Types registry and also creates
a PIM Message Type Flag Bits registry that shows which flag bits are
defined for use by each of the PIM message types.
The following changes should be made to the existing PIM Message
Types registry. For types 4 (Bootstrap) and 8 (Candidate RP
Advertisement) a reference to RFC5059 should be added. For type 15
(Reserved), the name should be changed to "Type Space Extension", and
reference this document. In addition, there should be one new row at
the bottom where it should say "15.0-15.15 Unassigned".
A new registry called "PIM Message Type Flag Bits" should be created
in the pim-paremeters section with registration procedure "IETF
Review" as defined in [RFC8126] with this document as a reference.
The initial content of the registry should be as below.
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Type bit(s) Name Reference
--------------------------------------------------------
0 0-7 Reserved [RFC3973][RFC7761]
1 0-7 Reserved [RFC3973][RFC7761]
2 0-7 Reserved [RFC3973][RFC7761]
3 0-7 Reserved [RFC3973][RFC7761]
4 0-6 Reserved [RFC3973][RFC7761]
4 7 No-Forward [RFC5059]
5 0-7 Reserved [RFC3973][RFC7761]
6 0-7 Reserved [RFC3973][RFC7761]
7 0-7 Reserved [RFC3973][RFC7761]
8 0-7 Reserved [RFC3973][RFC7761]
9 0-7 Reserved [RFC3973][RFC7761]
10 0-3 Reserved [RFC3973][RFC7761]
10 4-7 Sub-type [RFC5015]
11 0-7 Reserved [RFC6754]
12 0-6 Reserved [RFC3973][RFC7761]
12 7 No-Forward [draft-ietf-pim-source-discovery-bsr]
13 0-7 Reserved [RFC3973][RFC7761]
14 0-7 Reserved [RFC3973][RFC7761]
15 4-7 Extended type [this document]
15.0-15.15 0-3 Reserved [this document]
8. References
8.1. Normative References
[I-D.ietf-pim-source-discovery-bsr]
Wijnands, I., Venaas, S., Brig, M., and A. Jonasson, "PIM
Flooding Mechanism and Source Discovery", draft-ietf-pim-
source-discovery-bsr-12 (work in progress), January 2018.
[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>.
[RFC3973] Adams, A., Nicholas, J., and W. Siadak, "Protocol
Independent Multicast - Dense Mode (PIM-DM): Protocol
Specification (Revised)", RFC 3973, DOI 10.17487/RFC3973,
January 2005, <https://www.rfc-editor.org/info/rfc3973>.
[RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-
PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007,
<https://www.rfc-editor.org/info/rfc5015>.
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[RFC5059] Bhaskar, N., Gall, A., Lingard, J., and S. Venaas,
"Bootstrap Router (BSR) Mechanism for Protocol Independent
Multicast (PIM)", RFC 5059, DOI 10.17487/RFC5059, January
2008, <https://www.rfc-editor.org/info/rfc5059>.
[RFC6754] Cai, Y., Wei, L., Ou, H., Arya, V., and S. Jethwani,
"Protocol Independent Multicast Equal-Cost Multipath
(ECMP) Redirect", RFC 6754, DOI 10.17487/RFC6754, October
2012, <https://www.rfc-editor.org/info/rfc6754>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[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>.
8.2. Informative References
[RFC6166] Venaas, S., "A Registry for PIM Message Types", RFC 6166,
DOI 10.17487/RFC6166, April 2011,
<https://www.rfc-editor.org/info/rfc6166>.
Authors' Addresses
Stig Venaas
Cisco Systems, Inc.
Tasman Drive
San Jose CA 95134
USA
Email: stig@cisco.com
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Alvaro Retana
Huawei R&D USA
2330 Central Expressway
Santa Clara CA 95050
USA
Email: alvaro.retana@huawei.com
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