PIM Null-Register PackingVMware3401 Hillview AvePalo AltoCA94304United States of Americavkamath@vmware.comCisco Systems, Inc.Tasman DriveSan JoseCA95134United States of Americaramaksun@cisco.comApstraSuite 200333 Middlefield RdMenlo ParkCA94025United States of Americarbanthia@apstra.comCisco Systems, Inc.Tasman DriveSan JoseCA95134United States of Americaananygop@cisco.com
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pimMulticastIn PIM Sparse Mode (PIM-SM) networks, PIM Null-Register messages are sent by the Designated Router (DR) to the Rendezvous Point (RP) to signal the presence of multicast sources in the network. There are periodic PIM Null-Registers sent from the DR to the RP to keep the state alive at the RP as long as the source is active. The PIM Null-Register message carries information about a single multicast source and group.This document defines a standard to send information about multiple multicast sources and groups in a single PIM message. This document refers to the new messages as the "PIM Packed Null-Register message" and "PIM Packed Register-Stop message".Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 7841.
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
.
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Table of Contents
. Introduction
. Conventions Used in This Document
. Terminology
. Packing Capability
. PIM Packed Null-Register Message Format
. PIM Packed Register-Stop Message Format
. Protocol Operation
. Operational Considerations
. PIM Anycast RP Considerations
. Interoperability between Different Versions
. Disabling PIM Packed Message Support at RP and/or DR
. Fragmentation Considerations
. Security Considerations
. IANA Considerations
. Normative References
Acknowledgments
Authors' Addresses
IntroductionThe DR periodically sends PIM Null-Registers to keep the state of existing multicast sources active on the RP. As the number of multicast sources increases, the number of PIM Null-Register messages that are sent also increases. This results in more PIM packet processing at the RP and the DR.
This document specifies a method to efficiently pack the content
of multiple PIM Null-Register and Register-Stop messages
into a single message.
The document also discusses interoperability between PIM routers that support PIM Packed Null-Registers and PIM Packed Register-Stops and PIM routers that do not.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 when, and only when, they
appear in all capitals, as shown here.Terminology
RP:
Rendezvous Point
DR:
Designated Router
MSDP:
Multicast Source Discovery Protocol
PIM-SM:
PIM Sparse Mode
Packing Capability
The RP indicates its ability to receive PIM Packed Null-Register messages () and send PIM Packed Register-Stop messages () with a Packing Capability bit (P-bit) in the PIM Register-Stop message. The P-bit is allocated in .
PIM Register-Stop Message with Packing Capability Option
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|P| Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Address (Encoded-Group format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address (Encoded-Unicast format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Group Address and Source Address fields in the PIM Register-Stop message are defined in . The common header is defined in .
Packing Capability bit (P-bit; flag bit 0):
When set, it indicates the ability of the RP to receive PIM
Packed Null-Register messages and send PIM Packed Register-Stop
messages.
PIM Packed Null-Register Message FormatPIM Packed Null-Register Message Format
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 |Subtype| FB | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Address[1] (Encoded-Group format) |
| Source Address[1] (Encoded-Unicast format) |
. .
. .
. .
. .
. Group Address[N] .
| Source Address[N] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Group Address and Source Address fields in the PIM Packed Null-Register message are defined in
. The
common header is defined in .
Type, Subtype:
PIM Packed Null-Register (13.0).
N:
The total number of records; a record consists of a Group
Address and Source Address pair.
After parsing the PIM common header, individual records are then
parsed one by one until the end of the PIM Packed Null-Register
message. This length is inferred from the IP layer.
Sending or receiving a PIM Packed Null-Register message has the equivalent effect of sending or receiving an individual Null-Register message for each record
represented in the PIM Packed Null-Register message.PIM Packed Register-Stop Message FormatPIM Packed Register-Stop Message Format
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 |Subtype| FB | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Address[1] (Encoded-Group format) |
| Source Address[1] (Encoded-Unicast format) |
. .
. .
. .
. .
. Group Address[N] .
| Source Address[N] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Group Address and Source Address fields in the PIM Packed
Register-Stop message are defined in . The common header is defined in .
Type, Subtype:
PIM Packed Register-Stop (13.1).
N:
The total number of records; a record consists of a Group Address
and Source Address pair.
After parsing the PIM common header, individual records are then
parsed one by one until the end of the PIM Packed Register-Stop
message. This length is inferred from the IP layer. Sending or receiving a PIM Packed Register-Stop message has the equivalent effect of sending or receiving an individual Null-Register message for each record
represented in the PIM Packed Register-Stop.Protocol OperationAs specified in , the DR sends PIM Register messages towards the RP when a new source is detected. When this feature is enabled/configured, an RP supporting this specification MUST set the P-bit (flag bit 0) in all Register-Stop messages. When a Register-Stop message with the P-bit set is received, the DR
SHOULD send PIM Packed Null-Register messages () to the RP instead of multiple Register messages with
the N-bit set . The DR MAY use a
mixture of PIM Packed Null-Register messages and Register messages. The
decision is up to the implementation and out of the scope of this
document. However, it is RECOMMENDED to stick to the PIM
Packed Null-Register and PIM Packed Register-Stop formats as long as the
RP and DR have the feature enabled. After receiving a PIM Packed Null-Register message, the RP
SHOULD start sending PIM Packed Register-Stop messages
() to the corresponding DR instead of individual
Register-Stop messages. The RP MAY use a mixture of PIM
Packed Register-Stop messages and individual Register-Stop messages. The
decision is up to the implementation and out of the scope of this
document. However, it is RECOMMENDED to stick to the PIM
Packed Null-Register and PIM Packed Register-Stop formats as long as the
RP and DR have the feature enabled. Operational ConsiderationsPIM Anycast RP ConsiderationsThe PIM Packed Null-Register packet format should be enabled only
if it is supported by all the routers in the Anycast-RP set . This consideration applies to PIM Anycast RP with
Multicast Source Discovery Protocol (MSDP) as
well.
Interoperability between Different Versions A router (DR) can decide to use the PIM Packed Null-Register
message format based on the Packing Capability received from the RP as
part of the PIM Register-Stop. This ensures compatibility with routers
that do not support processing of the new packet format. The Packing
Capability information MUST be indicated by the RP via
the PIM Register-Stop message sent to the DR. Thus, a DR will switch
to the new packet format only when it learns that the RP is capable of
handling the PIM Packed Null-Register messages.
Conversely, a DR that does not support the packed format can
continue generating the PIM Null-Register as defined in .
Disabling PIM Packed Message Support at RP and/or DR Consider a PIM RP router that supports PIM Packed Null-Registers and PIM Packed Register-Stops. In scenarios where this router no longer supports this feature, for example, in case of a software downgrade, it will not send a PIM Register-Stop message to the DR in response to a PIM Packed Null-Register message.
When the DR switches to Data Registers from Null-Registers, it MUST start a Packed_Register_Probe_Time timer. If no PIM Packed Register-Stop or Register-Stop with the P-bit set is received within Packed_Register_Probe_Time seconds, the DR can decide that the RP no longer supports PIM Packed Null-Registers. The Packed_Register_Probe_Time timer is configurable; its default value is 60 seconds.
When Packed_Register_Probe_Time expires, the DR MAY also send an unpacked PIM Null-Register and check the PIM Register-Stop to see if the P-bit is set or not. If it is not set, then the DR will continue sending unpacked PIM Null-Register messages.In case the network manager disables the Packing Capability at the RP (or in other words, disables the feature from the RP), the router MUST NOT advertise the Packing Capability. However, an implementation MAY choose to still parse any packed registers if they are received. This may be particularly useful in the transitional period after the network manager disables it.Fragmentation Considerations As explained in , the DR may perform Path MTU Discovery to the RP
before sending PIM Packed Null-Register messages. Similarly, the RP may
perform Path MTU Discovery to the DR before sending PIM Packed
Register-Stop messages. In both cases, the number of records in a
message should be limited such that it can fit within the Path MTU.
Security Considerations The Security Considerations in apply to
this document. In particular, the effect of forging a PIM Packed
Null-Register or Register-Stop message would be amplified to all the
records included instead of just one. By forging a PIM Register-Stop message and setting the P-bit, an
attacker can trigger the use of PIM Packed Null-Register messages by a
DR, thus creating unnecessary churn in the network.IANA Considerations IANA has assigned a Packing
Capability bit (0) in the PIM Register-Stop common header in the
"PIM Message Types" registry. IANA has assigned a PIM
message type (13.0) for PIM Packed Null-Register in the "PIM
Message Types" registry. Flag bits 0-3 for this message type
are "Unassigned". IANA has assigned a PIM
message type (13.1) for PIM Packed Register-Stop in the "PIM
Message Types" registry. The flag bits 0-3 for this message type
are "Unassigned". Normative ReferencesKey words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Anycast Rendevous Point (RP) mechanism using Protocol Independent Multicast (PIM) and Multicast Source Discovery Protocol (MSDP)This document describes a mechanism to allow for an arbitrary number of Rendevous Points (RPs) per group in a single shared-tree Protocol Independent Multicast-Sparse Mode (PIM-SM) domain. This memo provides information for the Internet community.Anycast-RP Using Protocol Independent Multicast (PIM)This specification allows Anycast-RP (Rendezvous Point) to be used inside a domain that runs Protocol Independent Multicast (PIM) only. Other multicast protocols (such as Multicast Source Discovery Protocol (MSDP), which has been used traditionally to solve this problem) are not required to support Anycast-RP. [STANDARDS-TRACK]Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)This document specifies Protocol Independent Multicast - Sparse Mode (PIM-SM). PIM-SM is a multicast routing protocol that can use the underlying unicast routing information base or a separate multicast-capable routing information base. It builds unidirectional shared trees rooted at a Rendezvous Point (RP) per group, and it optionally creates shortest-path trees per source.This document obsoletes RFC 4601 by replacing it, addresses the errata filed against it, removes the optional (*,*,RP), PIM Multicast Border Router features and authentication using IPsec that lack sufficient deployment experience (see Appendix A), and moves the PIM specification to Internet Standard.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.PIM Message Type Space Extension and Reserved BitsThe 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 extends the PIM type space.This document updates RFCs 7761 and 3973 by defining the use of the Reserved field in the PIM common header. This document further updates RFCs 7761 and 3973, along with RFCs 5015, 5059, 6754, and 8364, by specifying the use of the bits for each PIM message.This document obsoletes RFC 8736.AcknowledgmentsThe authors would like to thank ,
, ,
, and
for their helpful comments on the document.Authors' AddressesVMware3401 Hillview AvePalo AltoCA94304United States of Americavkamath@vmware.comCisco Systems, Inc.Tasman DriveSan JoseCA95134United States of Americaramaksun@cisco.comApstraSuite 200333 Middlefield RdMenlo ParkCA94025United States of Americarbanthia@apstra.comCisco Systems, Inc.Tasman DriveSan JoseCA95134United States of Americaananygop@cisco.com