draft-ietf-pim-source-discovery-bsr-06.txt   draft-ietf-pim-source-discovery-bsr-07.txt 
Network Working Group IJ. Wijnands Network Working Group IJ. Wijnands
Internet-Draft S. Venaas Internet-Draft S. Venaas
Intended status: Experimental Cisco Systems, Inc. Intended status: Experimental Cisco Systems, Inc.
Expires: September 11, 2017 M. Brig Expires: June 23, 2018 M. Brig
Aegis BMD Program Office Aegis BMD Program Office
A. Jonasson A. Jonasson
Swedish Defence Material Administration (FMV) Swedish Defence Material Administration (FMV)
March 10, 2017 December 20, 2017
PIM flooding mechanism and source discovery PIM flooding mechanism and source discovery
draft-ietf-pim-source-discovery-bsr-06 draft-ietf-pim-source-discovery-bsr-07
Abstract Abstract
PIM Sparse-Mode uses a Rendezvous Point and shared trees to forward PIM Sparse-Mode uses a Rendezvous Point and shared trees to forward
multicast packets from new sources. Once last hop routers receive multicast packets from new sources. Once last hop routers receive
packets from a new source, they may join the Shortest Path Tree for packets from a new source, they may join the Shortest Path Tree for
the source for optimal forwarding. This draft defines a new the source for optimal forwarding. This draft defines a new
mechanism that provides a way to support PIM Sparse Mode (SM) without mechanism that provides a way to support PIM Sparse Mode (SM) without
the need for PIM registers, RPs or shared trees. Multicast source the need for PIM registers, RPs or shared trees. Multicast source
information is flooded throughout the multicast domain using a new information is flooded throughout the multicast domain using a new
skipping to change at page 1, line 35 skipping to change at page 1, line 35
learn about new sources without receiving initial data packets. learn about new sources without receiving initial data packets.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 11, 2017. This Internet-Draft will expire on June 23, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Testing and deployment experiences . . . . . . . . . . . . . 3 2. Testing and deployment experiences . . . . . . . . . . . . . 4
3. A generic PIM flooding mechanism . . . . . . . . . . . . . . 4 3. A generic PIM flooding mechanism . . . . . . . . . . . . . . 4
3.1. PFM message format . . . . . . . . . . . . . . . . . . . 5 3.1. PFM message format . . . . . . . . . . . . . . . . . . . 6
3.2. Processing PFM messages . . . . . . . . . . . . . . . . . 6 3.2. Administrative boundaries . . . . . . . . . . . . . . . . 7
3.2.1. Initial checks . . . . . . . . . . . . . . . . . . . 6 3.3. Originating PFM messages . . . . . . . . . . . . . . . . 7
3.2.2. Processing and forwarding of PFM messages . . . . . . 6 3.4. Processing PFM messages . . . . . . . . . . . . . . . . . 8
4. Distributing Source to Group Mappings . . . . . . . . . . . . 7 3.4.1. Initial checks . . . . . . . . . . . . . . . . . . . 9
4.1. Group Source Holdtime TLV . . . . . . . . . . . . . . . . 7 3.4.2. Processing and forwarding of PFM messages . . . . . . 9
4.2. Originating PFM messages . . . . . . . . . . . . . . . . 8 4. Distributing Source Group Mappings . . . . . . . . . . . . . 10
4.3. Processing GSH TLVs . . . . . . . . . . . . . . . . . . . 8 4.1. Group Source Holdtime TLV . . . . . . . . . . . . . . . . 10
4.4. The first packets and bursty sources . . . . . . . . . . 9 4.2. Originating Group Source Holdtime TLVs . . . . . . . . . 11
4.5. Resiliency to network partitioning . . . . . . . . . . . 10 4.3. Processing GSH TLVs . . . . . . . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 4.4. The first packets and bursty sources . . . . . . . . . . 12
6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 10 4.5. Resiliency to network partitioning . . . . . . . . . . . 13
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . 11 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . 11 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 8.1. Normative References . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
PIM Sparse-Mode uses a Rendezvous Point (RP) and shared trees to PIM Sparse-Mode uses a Rendezvous Point (RP) and shared trees to
forward multicast packets to Last Hop Routers (LHR). After the first forward multicast packets to Last Hop Routers (LHR). After the first
packet is received by a LHR, the source of the multicast stream is packet is received by a LHR, the source of the multicast stream is
learned and the Shortest Path Tree (SPT) can be joined. This draft learned and the Shortest Path Tree (SPT) can be joined. This draft
defines a new mechanism that provides a way to support PIM Sparse defines a new mechanism that provides a way to support PIM Sparse
Mode (SM) without the need for PIM registers, RPs or shared trees. Mode (SM) without the need for PIM registers, RPs or shared trees.
Multicast source information is flooded throughout the multicast Multicast source information is flooded throughout the multicast
domain using a new generic PIM flooding mechanism. By removing the domain using a new generic PIM flooding mechanism. By removing the
need for RPs and shared trees, the PIM-SM procedures are simplified, need for RPs and shared trees, the PIM-SM procedures are simplified,
improving router operations, management and making the protocol more improving router operations, management and making the protocol more
robust. Also the data packets are only sent on the SPTs, providing robust. Also the data packets are only sent on the SPTs, providing
optimal forwarding. optimal forwarding.
This document defines a generic flooding mechanism for distributing
information throughout a PIM domain. While the forwarding rules are
largely similar to Bootstrap Router mechanism (BSR) [RFC5059], any
router can originate information, and it allows for flooding of any
kind of information. Each message contains one or more pieces of
information encoded as TLVs (type, length and value). This document
defines one TLV used for distributing information about active
multicast sources. Other documents may define additional TLVs.
Note that this document is experimental. While the flooding
mechanism is largely similar to BSR, there are some concerns about
scale as there can be multiple routers distributing information, and
potentially larger amount of data that needs to be processed and
stored. Distributing knowledge of active sources in this way is new,
and there are some concerns, mainly regarding potentially large
amounts of source states that need to be distributed. While there
has been some testing in the field, we need to learn more about the
forwarding efficiency, both the amount of processing per router, and
propagation delay, and the amount of state that can be distributed.
In particular, how many active sources one can support without
consuming too many resources. There are also parameters that can be
tuned regarding how frequently information is distributed, and it is
not clear what parameters are useful for different types of networks.
1.1. Conventions used in this document 1.1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
1.2. Terminology 1.2. Terminology
RP: Rendezvous Point RP: Rendezvous Point
skipping to change at page 3, line 26 skipping to change at page 4, line 4
BSR: Bootstrap Router BSR: Bootstrap Router
RPF: Reverse Path Forwarding RPF: Reverse Path Forwarding
SPT: Shortest Path Tree SPT: Shortest Path Tree
FHR: First Hop Router, directly connected to the source FHR: First Hop Router, directly connected to the source
LHR: Last Hop Router, directly connected to the receiver LHR: Last Hop Router, directly connected to the receiver
PFM: PIM Flooding Mechanism PFM: PIM Flooding Mechanism
PFM-SA: PFM Source Announcement PFM-SA: PFM Source Announcement
SG Mapping: Multicast source to group mapping SG Mapping: Multicast source group mapping
2. Testing and deployment experiences 2. Testing and deployment experiences
A prototype of this specification has been implemented and there has A prototype of this specification has been implemented and there has
been some limited testing in the field. The prototype was tested in been some limited testing in the field. The prototype was tested in
a network with low bandwidth radio links. The network has frequent a network with low bandwidth radio links. The network has frequent
topology changes, including frequest link or router failures. topology changes, including frequest link or router failures.
Previously existing mechanisms like PIM-SM and PIM-DM were tested. Previously existing mechanisms like PIM-SM and PIM-DM were tested.
With PIM-SM the existing RP election mechanisms were found to be too With PIM-SM the existing RP election mechanisms were found to be too
skipping to change at page 4, line 14 skipping to change at page 4, line 38
rerouted as needed and there were no unnecessary forwarding of rerouted as needed and there were no unnecessary forwarding of
packets. Ease of configuration was seen as a plus. packets. Ease of configuration was seen as a plus.
3. A generic PIM flooding mechanism 3. A generic PIM flooding mechanism
The Bootstrap Router mechanism (BSR) [RFC5059] is a commonly used The Bootstrap Router mechanism (BSR) [RFC5059] is a commonly used
mechanism for distributing dynamic Group to RP mappings in PIM. It mechanism for distributing dynamic Group to RP mappings in PIM. It
is responsible for flooding information about such mappings is responsible for flooding information about such mappings
throughout a PIM domain, so that all routers in the domain can have throughout a PIM domain, so that all routers in the domain can have
the same information. BSR as defined, is only able to distribute the same information. BSR as defined, is only able to distribute
Group to RP mappings. We are defining a more generic mechanism that Group to RP mappings. This document defines a more generic mechanism
can flood any kind of information throughout a PIM domain. It is not that can flood any kind of information. Administrative boundaries
necessarily a domain though, it depends on the administrative Section 3.2 may be configured to limit to which parts of a network
boundaries being configured. The forwarding rules are identical to the information is flooded.
BSR, except that one can control whether routers should forward
unsupported data types. For some types of information it is quite The forwarding rules are identical to BSR, except that one can
useful that it can be distributed without all routers having to control whether routers should forward unsupported data types. For
support the particular type, while there may also be types where it some types of information it is quite useful that it can be
is necessary for every single router to support it. The mechanism distributed without all routers having to support the particular
includes an originator address which is used for RPF checking to type, while there may also be types where it is necessary for every
restrict the flooding, and prevent loops, just like BSR. Like BSR, single router to support it. The mechanism includes an originator
messages are forwarded hop by hop. Note that there is no equivalent address which is used for RPF checking to restrict the flooding, and
to the BSR election mechanism;, there can be multiple originators. prevent loops, just like BSR. Like BSR, messages are forwarded hop
We call this mechanism the PIM Flooding Mechanism (PFM). by hop. Note that there is no equivalent to the BSR election
mechanism;, there can be multiple originators. This mechanism is
named the PIM Flooding Mechanism (PFM).
3.1. PFM message format 3.1. PFM message format
0 1 2 3 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 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 |N| Reserved | Checksum | |PIM Ver| Type |N| Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator Address (Encoded-Unicast format) | | Originator Address (Encoded-Unicast format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type 1 | Length 1 | | Type 1 | Length 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value 1 | | Value 1 |
| . | | . |
skipping to change at page 5, line 29 skipping to change at page 6, line 29
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . | | . |
| . | | . |
| Type n | Length n | | Type n | Length n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value n | | Value n |
| . | | . |
| . | | . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PIM Version: Reserved, Checksum Described in [RFC7761]. PIM Version, Reserved and Checksum: As specified in [RFC7761].
Type: PIM Message Type. Value (pending IANA) for a PFM message. Type: PIM Message Type. Value (pending IANA) for a PFM message.
[N]o-Forward bit: When set, this bit means that the PFM message is [N]o-Forward bit: When set, this bit means that the PFM message is
not to be forwarded. not to be forwarded. This bit is defined to prevent Bootstrap
message forwarding in [RFC5059].
Originator Address: The address of the router that originated the Originator Address: The address of the router that originated the
message. This can be any address assigned to the originating message. This can be any address assigned to the originating
router, but MUST be routable in the domain to allow successful router, but MUST be routable in the domain to allow successful
forwarding. The format for this address is given in the Encoded- forwarding. The format for this address is given in the Encoded-
Unicast address in [RFC7761]. Unicast address in [RFC7761].
Type 1..n: A message contains one or more TLVs, in this case n Type 1..n: A message contains one or more TLVs, in this case n
TLVs. The Type specifies what kind of information is in the TLVs. The Type specifies what kind of information is in the
Value. Value. The type range is from 0 to 65535. A TLV with a type in
the range from 32768 to 65535 is never to be forwarded by an
implementation not supporting the type, see Section 3.4.2.
Length 1..n: The length of the the value field. Length 1..n: The length of the the value field in octets.
Value 1..n: The value associated with the type and of the specified Value 1..n: The value associated with the type and of the specified
length. length.
3.2. Processing PFM messages 3.2. Administrative boundaries
PFM messages are generally forwarded hop by hop to all PIM routers.
However, similar to BSR, one may configure administrative boundaries
to limit the information to certain domains or parts of the network.
Implementations MUST have a way of defining a set of interfaces on a
router as administrative boundaries for all PFM messages, or
optionally for certain TLVs, allowing for different boundaries for
different TLVs. Usually one wants boundaries to be bidirectional,
but an implementation MAY also provide unidirectional boundaries.
When forwarding a message, a router MUST NOT send it out an interface
that is an outgoing boundary, including bidirectional boundary, for
all PFM messages. If an interface is an outgoing boundary for
certain TLVs, the message MUST NOT be sent out the interface if it is
a boundary for all the TLVs in the message. Otherwise the router
MUST remove all the boundary TLVs from the message and send the
message with the remaining TLVs. Also, when receiving a PFM message
on an interface, the message MUST be discarded if the interface is an
incoming boundary, including bidirectional boundary, for all PFM
messages. If the interface is an incoming boundary for certain TLVs,
the router MUST ignore all boundary TLVs. If all the TLVs in the
message are boundary TLVs, then the message is effectively ignored.
Note that when forwarding an incoming message, the boundary is
applied before forwarding. If the message was discarded or all the
TLVs were ignored, then no message is forwarded. When a message is
forwarded, it MUST NOT contain any TLVs for which the incoming
interface is an incoming, or bidirectional, boundary.
3.3. Originating PFM messages
A router originates a PFM message when it needs to distribute
information using a PFM message to other routers in the network.
When a message is originated depends on what information is
distributed. For instance this document defines a TLV to distribute
information about active sources. When a router has a new active
source, a PFM message should be sent as soon as possible. Hence a
PFM message should be sent every time there is a new active source.
However, the TLV also contains a holdtime and PFM messages need to be
sent periodically. Generally speaking, a PFM message would typically
be sent when there is a local state change, causing information to be
distributed with PFM to change. Also, some information may need to
be sent periodically. These messages are called triggered and
periodic messages, respectively. Each TLV definition will need to
define when a triggered PFM message needs to be originated, and also
whether to send periodic messages, and how frequent.
Unless otherwise specified by the TLV definitions, there is no
relationship between different TLVs, and an implementation can choose
whether to combine TLVs in one message or across separate messages.
It is RECOMMENDED to combine multiple TLVs in one message, to reduce
the number of messages, but it is also RECOMMENDED that the message
is small enough to avoid fragmentation at the IP layer. When a
triggered PFM message needs to be sent due to a state change, a
router MAY send a message containing only the information that
changed. If there are many changes occuring at about the same time,
it might be possible to combine multiple changes in one message. In
the case where periodic messages are also needed, an implementation
MAY include periodic PFM information in a triggered PFM. E.g., if
some information needs to be sent every 60 seconds and a triggered
PFM is about to be sent 20 seconds before the next periodic PFM was
scheduled, the triggered PFM might include the periodic information
and the next periodic PFM can then be scheduled 60 seconds after
that, rather than 20 seconds later.
When a router originates a PFM message, it puts one of its own
addresses in the originator field. An implementation MUST allow an
administrator to configure which address is used. For a message to
be received by all routers in a domain, all the routers need to have
a route for this address due to the RPF based forwarding. Hence an
administrator needs to be careful which address to choose. When this
is not configured, an implementation MUST NOT use a link-local
address. It is RECOMMENDED to use an address of a virtual interface
such that the originator can remain unchanged and routable
independent of which physical interfaces or links may go down.
The No-Forward bit MUST NOT be set, except for the case when a router
receives a PIM Hello from a new neighbor, or a PIM Hello with a new
GenID is received from an existing neighbor. In that case an
implementation MAY send PFM messages containing relevant information
so that the neighbor can quickly get the correct state. The
definition of the different PFM message TLVs need to specify what, if
anything, needs to be sent in this case. If such a PFM message is
sent, the No-Forward bit MUST be set, and the message must be sent
within 60 seconds after the neighbor state change. The processing
rules for PFM messages will ensure that any other neighbors on the
same link ignores the message.
3.4. Processing PFM messages
A router that receives a PFM message MUST perform the initial checks A router that receives a PFM message MUST perform the initial checks
specified here. If the checks fail, the message MUST be dropped. An specified here. If the checks fail, the message MUST be dropped. An
error MAY be logged, but otherwise the message MUST be dropped error MAY be logged, but otherwise the message MUST be dropped
silently. If the checks pass, the contents is processed according to silently. If the checks pass, the contents is processed according to
the processing rules of the included TLVs. the processing rules of the included TLVs.
3.2.1. Initial checks 3.4.1. Initial checks
In order to do further processing, a message MUST meet the following In order to do further processing, a message MUST meet the following
requirements. The message MUST be from a directly connected neighbor requirements. The message MUST be from a directly connected PIM
for which we have active Hello state, and it MUST have been sent to neighbor, the destination address MUST be ALL-PIM-ROUTERS. Also, the
the ALL-PIM-ROUTERS group. Also, the interface MUST NOT be an interface MUST NOT be an incoming, nor bidirectional, administrative
administrative boundary for PFM. If No-Forward is not set, it MUST boundary for PFM messages Section 3.2. If No-Forward is not set, the
have been sent by the RPF neighbor for the originator address. If message MUST be from the RPF neighbor of the originator address. If
No-Forward is set, we MUST have restarted within 60 seconds. In No-Forward is set, this system, the router doing these checks, MUST
pseudo-code the algorithm is as follows: have restarted within 60 seconds. In pseudo-code the algorithm is as
follows:
if ((DirectlyConnected(PFM.src_ip_address) == FALSE) OR if ((DirectlyConnected(PFM.src_ip_address) == FALSE) OR
(we have no Hello state for PFM.src_ip_address) OR (PFM.src_ip_address is not a PIM neighbor) OR
(PFM.dst_ip_address != ALL-PIM-ROUTERS) OR (PFM.dst_ip_address != ALL-PIM-ROUTERS) OR
(Incoming interface is admin boundary for PFM)) { (Incoming interface is admin boundary for PFM)) {
drop the message silently, optionally log error. drop the message silently, optionally log error.
} }
if (PFM.no_forward_bit == 0) { if (PFM.no_forward_bit == 0) {
if (PFM.src_ip_address != if (PFM.src_ip_address !=
RPF_neighbor(PFM.originator_ip_address)) { RPF_neighbor(PFM.originator_ip_address)) {
drop the message silently, optionally log error. drop the message silently, optionally log error.
} }
} else if (more than 60 seconds elapsed since startup)) { } else if (more than 60 seconds elapsed since startup)) {
drop the message silently, optionally log error. drop the message silently, optionally log error.
} }
Note that src_ip_address is the source address in the IP header of Note that src_ip_address is the source address in the IP header of
the PFM message. Originator is the originator field inside the PFM the PFM message. Originator is the originator field inside the PFM
message, and is the router that originated the message. When the message, and is the router that originated the message. When the
message is forwarded hop by hop, the originator address never message is forwarded hop by hop, the originator address never
changes, while the source address will be an address belonging to the changes, while the source address will be an address belonging to the
router that last forwarded the message. router that last forwarded the message.
3.2.2. Processing and forwarding of PFM messages 3.4.2. Processing and forwarding of PFM messages
When the message is received, the initial checks above must be When the message is received, the initial checks above must be
performed. If it passes the checks, we then for each included TLV performed. If it passes the checks, then for each included TLV,
perform processing according to the specification for that TLV. perform processing according to the specification for that TLV.
After processing, we forward the message. Unless otherwise specified After processing, the messsage is forwarded. Unless otherwise
by the type specification, the TLVs in the forwarded message are specified by the type specification, the TLVs in the forwarded
identical to the TLVs in the received message. However, if the most message are identical to the TLVs in the received message. However,
significant bit in the type field is set (the type value is larger if the most significant bit in the type field is set (the type value
than 32767) and we do not support the type, then that particular type is larger than 32767) and this system does not support the type, then
should be omitted from the forwarded messages. The message is that particular type should be omitted from the forwarded messages.
forwarded out of all interfaces with PIM neighbors (including the The message is forwarded out of all interfaces with PIM neighbors
interface it was received on). (including the interface it was received on).
4. Distributing Source to Group Mappings 4. Distributing Source Group Mappings
The generic flooding mechanism (PFM) defined in the previous section The generic flooding mechanism (PFM) defined in the previous section
can be used for distributing source to group mappings about active can be used for distributing source group mappings about active
multicast sources throughout a PIM domain. A Group Source Holtime multicast sources throughout a PIM domain. A Group Source Holtime
(GSH) TLV is defined for this purpose. (GSH) TLV is defined for this purpose.
4.1. Group Source Holdtime TLV 4.1. Group Source Holdtime TLV
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0 | Length | | Type = 0 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Address (Encoded-Group format) | | Group Address (Encoded-Group format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Src Count | Src Holdtime | | Src Count | Src Holdtime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Src Address 1 (Encoded-Unicast format) | | Src Address 1 (Encoded-Unicast format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Src Address 2 (Encoded-Unicast format) | | Src Address 2 (Encoded-Unicast format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . | | . |
| . | | . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Src Address m (Encoded-Unicast format) | | Src Address m (Encoded-Unicast format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: This TLV has type 0. Type: This TLV has type 0.
Length: The length of the value. Length: The length of the value in octets.
Group Address: The group we are announcing sources for. The format Group Address: The group that sources are to be announced for. The
for this address is given in the Encoded-Group format in format for this address is given in the Encoded-Group format in
[RFC7761]. [RFC7761].
Src Count: How many unicast encoded sources address encodings Src Count: How many unicast encoded sources address encodings
follow. follow.
Src Holdtime: The Holdtime (in seconds) for the corresponding Src Holdtime: The Holdtime (in seconds) for the corresponding
source(s). source(s).
Src Address: The source address for the corresponding group. The Src Address: The source address for the corresponding group. The
format for these addresses is given in the Encoded-Unicast address format for these addresses is given in the Encoded-Unicast address
in [RFC7761]. in [RFC7761].
4.2. Originating PFM messages 4.2. Originating Group Source Holdtime TLVs
A PFM message MAY contain one or more Group Source Holdtime (GSH) A PFM message MAY contain one or more Group Source Holdtime (GSH)
TLVs. This is used to flood information about active multicast TLVs. This is used to flood information about active multicast
sources. Each FHR that is directly connected to an active multicast sources. Each FHR that is directly connected to an active multicast
source originates PFM messages containing GSH TLVs. How a multicast source originates PFM messages containing GSH TLVs. How a multicast
router discovers the source of the multicast packet and when it router discovers the source of the multicast packet and when it
considers itself the FHR follows the same procedures as the considers itself the FHR follows the same procedures as the
registering process described in [RFC7761]. When a FHR has decided registering process described in [RFC7761]. When a FHR has decided
that a register needs to be sent per [RFC7761], the SG is not that a register needs to be sent per [RFC7761], the SG is not
registered via the PIM SM register procedures, but the SG mapping is registered via the PIM SM register procedures, but the SG mapping is
included in an GSH TLV in a PFM message. Note, only the SG mapping included in an GSH TLV in a PFM message. Note, only the SG mapping
is distributed in the message, not the entire packet as would have is distributed in the message, not the entire packet as would have
been done with a PIM register. The router originating the PFM been done with a PIM register. The PFM messages containing the GSH
messages includes one of its own addresses in the originator field. TLV are periodically sent for as long as the multicast source is
Note that this address SHOULD be routeable due to RPF checking. The active, similar to how PIM registers are periodically sent. The
PFM messages containing the GSH TLV are periodically sent for as long default announcement period is 60 seconds, which means that as long
as the multicast source is active, similar to how PIM registers are as the source is active, it is included in a PFM message originated
periodically sent. The default announcement period is 60 seconds, every 60 seconds. The holdtime for the source is by default 210
which means that as long as the source is active, it is included in a seconds. Other values MAY be configured, but the holdtime MUST be
PFM message originated every 60 seconds. The holdtime for the source either zero, or larger than the announcement period. It is
is by default 210 seconds. Other values MAY be configured, but the RECOMMENDED to be 3.5 times the announcement period. A source MAY be
holdtime MUST be either zero, or larger than the announcement period. announced with a holdtime of zero to indicate that the source is no
It is RECOMMENDED to be 3.5 times the announcement period. A source longer active.
MAY be announced with a holdtime of zero to indicate that the source
is no longer active.
If an implementation supports originating GSH TLVs with different If an implementation supports originating GSH TLVs with different
holdtimes for different sources, it can if needed send multiple TLVs holdtimes for different sources, it can if needed send multiple TLVs
with the same group address. Due to the format, all the sources in with the same group address. Due to the format, all the sources in
the same TLV have the same holdtime. the same TLV have the same holdtime.
When a new source is detected, an implementation MAY send a PFM
message containing just that particular source. However, it MAY also
include information about other sources that were just detected, so
sources that are scheduled for periodic announcement later, or other
types of information. See Section 3.3 for details.
When a new PIM neighbor is detected, or an existing neighbor changes
GenID, an implementation MAY send a triggered PFM message containing
GSH TLVs for any Source Group mappings it has learned by receiving
PFM GSH TLVs as well as any active directly connected sources. See
Section 3.3 for further details.
4.3. Processing GSH TLVs 4.3. Processing GSH TLVs
A router that receives a PFM message containing GSH TLVs SHOULD parse A router that receives a PFM message containing GSH TLVs MUST parse
the message and store each of the GSH TLVs as SG mappings with a the GSH TLVs and store each of the GSH TLVs as SG mappings with a
holdtimer started with the advertised holdtime. For each group that holdtimer started with the advertised holdtime, unless the
has directly connected receivers, this router SHOULD send PIM (S,G) implementation specifically does not support GSH TLVs, the router is
joins for all the SG mappings advertised in the message for the configured to ignore GSH TLVs in general, or to ignore GSH TLVs for
group. The SG mappings are kept alive for as long as the holdtimer certain sources or groups. In particular, an administrator might
configure a router to not process GSH TLVs if the router is known to
never have any directly connected receivers.
For each group that has directly connected receivers, this router
SHOULD send PIM (S,G) joins for all the SG mappings advertised in the
message for the group. Generally joins are sent, but there could for
instance be administrative policy limiting which sources and groups
to join. The SG mappings are kept alive for as long as the holdtimer
for the source is running. Once the holdtimer expires a PIM router for the source is running. Once the holdtimer expires a PIM router
MAY send a PIM (S,G) prune to remove itself from the tree. However, MAY send a PIM (S,G) prune to remove itself from the tree. However,
when this happens, there should be no more packets sent by the when this happens, there should be no more packets sent by the
source, so it may be desirable to allow the state to time out rather source, so it may be desirable to allow the state to time out rather
than sending a prune. than sending a prune.
Note that a holdtime of zero has a special meaning. It is to be Note that a holdtime of zero has a special meaning. It is to be
treated as if the source just expired, and state to be removed. treated as if the source just expired, and state to be removed.
Source information MUST NOT be removed due to the source being Source information MUST NOT be removed due to the source being
omitted in a message. For instance, if there is a large number of omitted in a message. For instance, if there is a large number of
skipping to change at page 9, line 45 skipping to change at page 13, line 8
But in reality this is not always the case. But in reality this is not always the case.
With the procedures defined in this document the packet(s) received With the procedures defined in this document the packet(s) received
by the FHR will be dropped until the LHR has learned about the source by the FHR will be dropped until the LHR has learned about the source
and the SPT is built. That means for bursty sources or applications and the SPT is built. That means for bursty sources or applications
sensitive for the delivery of the first packet this solution would sensitive for the delivery of the first packet this solution would
not be very applicable. This solution is mostly useful for not be very applicable. This solution is mostly useful for
applications that don't have strong dependency on the initial applications that don't have strong dependency on the initial
packet(s) and have a fairly constant data rate, like video packet(s) and have a fairly constant data rate, like video
distribution for example. For applications with strong dependency on distribution for example. For applications with strong dependency on
the initial packet(s) we recommend using PIM Bidir [RFC5015] or SSM the initial packet(s) using PIM Bidir [RFC5015] or SSM [RFC4607] is
[RFC4607]. The protocol operations are much simpler compared to PIM recommended. The protocol operations are much simpler compared to
SM, it will cause less churn in the network and both guarantee best PIM SM, it will cause less churn in the network and both guarantee
effort delivery for the initial packet(s). best effort delivery for the initial packet(s).
4.5. Resiliency to network partitioning 4.5. Resiliency to network partitioning
In a PIM SM deployment where the network becomes partitioned, due to In a PIM SM deployment where the network becomes partitioned, due to
link or node failure, it is possible that the RP becomes unreachable link or node failure, it is possible that the RP becomes unreachable
to a certain part of the network. New sources that become active in to a certain part of the network. New sources that become active in
that partition will not be able to register to the RP and receivers that partition will not be able to register to the RP and receivers
within that partition are not able to receive the traffic. Ideally within that partition are not able to receive the traffic. Ideally
you would want to have a candidate RP in each partition, but you you would want to have a candidate RP in each partition, but you
never know in advance which routers will form a partitioned network. never know in advance which routers will form a partitioned network.
In order to be fully resilient, each router in the network may end up In order to be fully resilient, each router in the network may end up
being a candidate RP. This would increase the operational complexity being a candidate RP. This would increase the operational complexity
of the network. of the network.
The solution described in this document does not suffer from that The solution described in this document does not suffer from that
problem. If a network becomes partitioned and new sources become problem. If a network becomes partitioned and new sources become
active, the receivers in that partitioned will receive the SG active, the receivers in that partitioned will receive the SG
Mappings and join the source tree. Each partition works Mappings and join the source tree. Each partition works
independently of the other partition(s) and will continue to have independently of the other partition(s) and will continue to have
access to sources within that partition. As soon as the network access to sources within that partition. Once the network has
heals, the SG Mappings are re-flooded into the other partition(s) and healed, the periodic flooding of SG Mappings ensures that they are
other receivers can join to the newly learned sources. re-flooded into the other partition(s) and other receivers can join
to the newly learned sources.
5. Security Considerations 5. Security Considerations
The security considerations are mainly similar to what is documented When it comes to general PIM message security, see [RFC7761]. PFM
in [RFC5059]. It is a concern that rogue devices can inject packets messages MUST only be accepted from a PIM neighbor, but as discussed
that are flooded throughout a domain. PFM packets must only be in [RFC7761], any router can become a PIM neighbor by sending a Hello
accepted from a PIM neighbor. Deployments may use mechanisms for message. To control from where to accept PFM packets, one can limit
authenticating PIM neighbors. For PFM-SA it is an issue that which interfaces PIM is enabled, and also one can configure
injected packets from a rogue device could send SG mappings for a interfaces as administrative boundaries for PFM messages, see
large number of source addresses, causing routers to use memory Section 3.2. The implications of forged PFM messages depend on which
storing these mappings, and also if they have interest in the groups, TLVs they contain. Documents defining new TLVs will need to discuss
build Shortest Path Trees for sources that are not actually active. the security considerations for the specific TLVs. In general
though, the PFM messages are flooded within the network, and by
forging a large number of PFM messages one might stress all the
routers in the network.
If an attacker can forge PFM messages, then such messages may contain
arbitrary GSH TLVs. An issue here is that an attacker might send
such TLVs for a huge amount of sources, potentially causing every
router in the network to store huge amounts of source state. Also,
if there is receiver interest for the groups specified in the GSH
TLVs, routers with directly connected receivers will build Shortest
Path Trees for the announced sources, even if the sources are
actually active. Building such trees will consume additional
resources on routers that the trees pass through.
6. IANA considerations 6. IANA considerations
This document requires the assignment of a new PIM message type for This document requires the assignment of a new PIM message type for
the PIM Flooding Mechanism (PFM). IANA is also requested to create a the PIM Flooding Mechanism (PFM). IANA is also requested to create a
registry for PFM TLVs, with type 0 assigned to the "Source Group registry for PFM TLVs, with type 0 assigned to the "Source Group
Holdtime" TLV. Values in the range 1-65535 are "Unassigned". Holdtime" TLV. Values in the range from 1 to 65535 are "Unassigned".
Assignments for the registry are to be made according to the policy Assignments for the registry are to be made according to the policy
"IETF Review" as defined in [RFC5226]. "IETF Review" as defined in [RFC8126].
7. Acknowledgments 7. Acknowledgments
The authors would like to thank Arjen Boers for contributing to the The authors would like to thank Arjen Boers for contributing to the
initial idea, and Yiqun Cai and Dino Farinacci for their comments on initial idea, and Yiqun Cai and Dino Farinacci for their comments on
the draft. the draft.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC5059] Bhaskar, N., Gall, A., Lingard, J., and S. Venaas, [RFC5059] Bhaskar, N., Gall, A., Lingard, J., and S. Venaas,
"Bootstrap Router (BSR) Mechanism for Protocol Independent "Bootstrap Router (BSR) Mechanism for Protocol Independent
Multicast (PIM)", RFC 5059, DOI 10.17487/RFC5059, January Multicast (PIM)", RFC 5059, DOI 10.17487/RFC5059, January
2008, <http://www.rfc-editor.org/info/rfc5059>. 2008, <https://www.rfc-editor.org/info/rfc5059>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <http://www.rfc-editor.org/info/rfc7761>. 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>.
8.2. Informative References 8.2. Informative References
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
<http://www.rfc-editor.org/info/rfc4607>. <https://www.rfc-editor.org/info/rfc4607>.
[RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR- "Bidirectional Protocol Independent Multicast (BIDIR-
PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007,
<http://www.rfc-editor.org/info/rfc5015>. <https://www.rfc-editor.org/info/rfc5015>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
Authors' Addresses Authors' Addresses
IJsbrand Wijnands IJsbrand Wijnands
Cisco Systems, Inc. Cisco Systems, Inc.
De kleetlaan 6a De kleetlaan 6a
Diegem 1831 Diegem 1831
Belgium Belgium
Email: ice@cisco.com Email: ice@cisco.com
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