Internet DRAFT - draft-ietf-pim-light
draft-ietf-pim-light
Network Working Group H. Bidgoli, Ed.
Internet-Draft Nokia
Intended status: Standards Track S. Venaas
Expires: 29 August 2024 Cisco System, Inc.
M. Mishra
Cisco System
Z. Zhang
Juniper Networks
M. McBride
Futurewei Technologies Inc.
26 February 2024
PIM Light
draft-ietf-pim-light-02
Abstract
This document specifies a new Protocol Independent Multicast
interface which does not need PIM Hello to accept PIM Join/Prunes.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 2
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
3. PIM Light Interface . . . . . . . . . . . . . . . . . . . . . 3
3.1. PLI supported Messages . . . . . . . . . . . . . . . . . 3
3.2. Lack of Hello Message consideration . . . . . . . . . . . 4
3.2.1. Join Attribute . . . . . . . . . . . . . . . . . . . 4
3.2.2. DR Selection . . . . . . . . . . . . . . . . . . . . 4
3.2.3. PIM Assert . . . . . . . . . . . . . . . . . . . . . 4
3.3. PLI Configuration . . . . . . . . . . . . . . . . . . . . 5
3.4. Failures in PLR domain . . . . . . . . . . . . . . . . . 5
3.5. Reliable Transport Mechanism for PIM LIGHT . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
It might be desirable to create a PIM interface between routers where
only PIM Join/Prunes packets are signaled over it without having a
full PIM neighbor discovery. As an example, this type of PIM
interface can be useful in some scenarios where the multicast state
needs to be signaled over a network or medium which is not capable of
or has no need for creating full PIM neighborship between its Peer
Routers. These type of PIM interfaces are called PIM Light
Interfaces (PLI).
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.
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2.1. Definitions
This draft uses definitions used in [RFC7761]
3. PIM Light Interface
RFC [RFC7761] section 4.3.1 describes the PIM neighbor discovery via
Hello messages. It also describes that PIM Join/Prune are not
accepted from a router unless a Hello message has been seen from that
router.
In some scenarios it is desirable to communicate and build multicast
states between two L3 adjacent routers without establishing a PIM
neighborship. There could be many reasons for this desired, but one
example is the desired to signal multicast states upstream, between
two or more PIM Domains via a network or medium that is not optimized
for PIM or does not require PIM Neighbor establishment. An example
is a BIER network connecting multiple PIM domains. In these BIER
networks PIM Join/prune messages are tunneled via bier as per
[draft-ietf-bier-pim-signaling].
A PIM Light Interface (PLI) ONLY accepts Join/Prune messages from an
unknown PIM router and it accepts these messages without receiving a
PIM Hello message form the router. Lack of Hello Messages on a PLI
means there is no mechanism to learn about the neighboring PIM
routers on each interface and their capabilities or run some of the
basic algorithms like DR Election between the routers. As such the
PIM light router doesn't create any General-Purpose state for
neighboring PIM and it only process Join/Prune message from
downstream routers in its multicast routing table.
Because of this, a PLI needs to be created in very especial cases and
the application that is using these PLIs should ensure there is no
multicast duplication of packets. As an example, multiple upstream
routers sending the same multicast stream to a single downstream
router.
3.1. PLI supported Messages
As per IANA [iana_pim-parameters] PIM supports more than 12 message
types, PIM Light only supports message type 3 (Join/Prune) from the
ALL-PIM-ROUTERS message types listed in RFC7761, other unicast
destination message types are supported by PIM light. All other
message types are not supported for PIM Light and should not be
process if received on a PLI.
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3.2. Lack of Hello Message consideration
The following should be considered on a PIM Light domain since hello
messages are not processed.
3.2.1. Join Attribute
Since PLI does not process the pim hello message, processing of the
join attributes option in pim hello as per [RFC5384] is also not
supported, leaving PIM Light unaware of its neighbor capability of
processing the join attribute. A PIM Light Router that does not
understand the type 1 Encoded-source Address and per [RFC7761] should
not process a join message that contains it. Otherwise the PLI can
process the Join Attribute accordingly.
3.2.2. DR Selection
Since DR Election is not supported on PIM Light because of lack of
hello messages, the network design should ensure that DR Election is
achieve on the PIM domain, assuming the PIM Light domain is
connecting PIM domains.
As an example, in a BIER domain which is connecting 2 PIM networks, a
PLI can be used between the BIER edge routers. The PLI will be only
used for multicast states communication, by transmitting ONLY PIM
Join/prunes over the BIER domain. In this case to ensure there is no
multicast stream duplication the PIM routers attached on each side of
the BIER domain might want to establish PIM Adjacency via [RFC7761]
to ensure DR election on the edge of the BIER router, while PLI is
used in the BIER domain, between BIER edge routers. When the Join or
Prune message arrives from a PIM domain to the down stream BIER edge
router, it can be send over the BIER tunnel to the upstream BIER edge
router only via the selected designated router.
3.2.3. PIM Assert
Where multiple PIM routers peer over a shared LAN or a Point-to-
Multipoint medium, it is possible for more than one upstream router
to have valid forwarding state for a packet, which can lead to packet
duplication. When this is detected PIM Assert is used to select one
transmitter. That said as per [RFC7761] PIM Assert should only be
accepted if it comes from a known PIM neighbor. With PIM LIGHT the
implementation SHOULD ensure there is no duplicate streams arriving
from upstream PIM Light routers to a single downstream PIM LIGHT
router. If this condition is not possible to be met because of
network design, the implementation should ensure there is no
duplication of stream. As an example in PIM LIGHT over a BIER domain
implementation, for IBBR (Down stream PIM LIGHT router) in a BIER
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domain to find the EBBRs closes to the source (upstream PIM LIGHT
routes), SPF can be use with a post processing as per
[draft-ietf-bier-pim-signaling] Appendix A.1. With this post
processing if 2 EBBRs are found by the downstream IBBR, then this
down stream IBBR router can choose one of the EBBRs with a unique IP
selection algorithm. As an example the EBBR with lowest IP address
or largest IP address can be the EBBR that the downstream PIM LIGHT
(IBBR) router sends the join/prune message to. When this EBBR goes
offline the downstream router can send the join to the next EBBR
based on the IP selection algorithm. This IP selection algorithm is
outside of scope of this draft.
3.3. PLI Configuration
Since a PLI doesn't require PIM Hello Messages and PIM neighbor
adjacency is not checked for join/prune messages, there needs to be a
mechanism to enable PLI on interfaces for security purpose, while on
some other interfaces this may be enabled automatically. An example
of the latter is the logical interface for a BIER sub-domain
[draft-ietf-bier-pim-signaling].
If a system explicitly needs a PLI to be configured, then this system
should not accepts the Join/Prune messages on interfaces that the PLI
is not configured on, and it should drop these messages on a non PLI
interface. If the system automatically enables PLI on some special
interfaces, as an example interfaces facing a BIER domain, then it
should accept Join/Prune messages on these interfaces only.
3.4. Failures in PLR domain
Because the hello messages are not processed on the PLI, some
failures may not be discovered in PLI domain and multicast routes
will not be pruned toward the source on the PIM domain, leaving the
upstream routers continuously sending multicast streams until the out
going interface (OIF) expires.
Other protocols can be used to detect these failures in the PIM Light
domain and they can be implementation specific. As an example, the
interface that PIM Light is configured on can be protected via BFD or
similar technology. If BFD to the far-end PLI goes down, and the Pim
Light Router is upstream and is an OIF for a multicast route <S,G>,
PIM should remove that PLI from its OIF list. In addition if
upstream PLI is configured automatically, as an example in BIER case,
when the downstream BFR is no longer reachable, the upstream PIM
Light Router can prune the <S,G> advertised by that BFR, toward the
source to stop the transmission of the multicast stream.
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3.5. Reliable Transport Mechanism for PIM LIGHT
[RFC6559] defines a reliable transport mechanism for PIM transmission
of Join/Prune messages. PIM over reliable transport (PORT) uses TCP
port 8471 which is assigned by IANA. [RFC6559] mandates that if a
router is configured to use PIM over TCP or SCTP on a given interface
it must include the PIM-over-TCP-Capable or PIM-over-SCTP-Capable
hello option in its Hello messages for that interface. These options
also communicate the connection ID of TCP for the appropriate address
family. PIM light lacking Hello messages, can be configured to use
PORT under a PLI. That said the TCP connection ID of local router
and peer router has to be configured manually under each side of the
PLI. The PLI uses these local and peer connection ID to setup a TCP
connection. As per [RFC6559] section 4 the routers use the
connection IDs to figure out which side will do a passive transport
open and which side of the PLI with do a active open. If TCP
connection failed to open then PLI will revert back to Datagram mode.
4. IANA Considerations
5. Security Considerations
Since PIM Light can be used for signaling Source-Specific and Sparse
Mode Join/Prune messages, security considerations of [RFC7761] and
[RFC4607] SHOULD be considered.
It should be noted a PIM Light can also use [RFC5796] as indicated in
[RFC7761] for authentication.
6. Acknowledgments
Would like to thank Sandy <Zhang Zheng> for her suggestions and
contribution to this draft.
7. References
7.1. Normative References
[draft-ietf-bier-pim-signaling]
"H.Bidgoli, F.XU, J. Kotalwar, I. Wijnands, M.Mishra, Z.
Zhang, "PIM Signaling Through BIER Core"", July 2021.
[iana_pim-parameters]
"", January 2022.
[RFC2119] "S. Brandner, "Key words for use in RFCs to Indicate
Requirement Levels"", March 1997.
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[RFC4607] "H. Holbrook, B. Cain "Source-Specific Multicast for IP"".
[RFC5384] "A. Boers, I. Wijnands, E. Rosen "PIM Join Attribute
Format"", March 2016.
[RFC5796] "W. Atwood, S. Islam, M. Siami "Authentication and
Confidentiality in PIM-SM"".
[RFC6559] "D. Farinacci, I. Wijnands, S. Venaas, M. Napierala "A
reliable Transport Mechanism for PIM"".
[RFC7761] "B.Fenner, M.Handley, H. Holbrook, I. Kouvelas, R. Parekh,
Z.Zhang "PIM Sparse Mode"", March 2016.
[RFC8174] "B. Leiba, "ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words"", May 2017.
7.2. Informative References
[RFC8279] "Wijnands, IJ., Rosen, E., Dolganow, A., Przygienda, T.
and S. Aldrin, "Multicast using Bit Index Explicit
Replication"", October 2016.
Authors' Addresses
Hooman Bidgoli (editor)
Nokia
March Road
Ottawa Ontario K2K 2T6
Canada
Email: hooman.bidgoli@nokia.com
Stig
Cisco System, Inc.
Tasman Drive
San Jose, California 95134
United States of America
Email: stig@cisco.com
Mankamana Mishra
Cisco System
Tasman Drive
San Jose, California 95134
United States of America
Email: mankamis@cisco.com
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Zhaohui Zhang
Juniper Networks
Boston,
United States of America
Email: zzhang@juniper.com
Mike
Futurewei Technologies Inc.
Santa Clara,
United States of America
Email: michael.mcbride@futurewei.com
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