Network Working Group Dino Farinacci
Internet-Draft IJsbrand Wijnands
Intended status: Experimental Apoorva Karan
Expires: November 21, 2008 Arjen Boers
cisco Systems
Maria Napierala
AT&T Labs
May 20, 2008
A Reliable Transport Mechanism for PIM
draft-farinacci-pim-port-01.txt
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Abstract
This draft describes how a reliable transport mechanism can be used
by the PIM protocol to optimize CPU and bandwidth resource
utilization by eliminating periodic Join/Prune message transmission.
This draft proposes a modular extension to PIM to use either the TCP
or SCTP transport protocol.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 5
1.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7
3. New PIM Hello Options . . . . . . . . . . . . . . . . . . . . 8
3.1. PIM over the TCP Transport Protocol . . . . . . . . . . . 8
3.2. PIM over the SCTP Transport Protocol . . . . . . . . . . . 9
4. Establishing Transport Connections . . . . . . . . . . . . . . 10
4.1. TCP Connection Maintenance . . . . . . . . . . . . . . . . 11
4.2. Transitional Periods . . . . . . . . . . . . . . . . . . . 11
4.3. On-demand versus Pre-configured Connections . . . . . . . 12
4.4. Possible Hello Suppression Considerations . . . . . . . . 12
4.5. Avoiding a Pair of Connections between Neighbors . . . . . 13
5. Common Header Definition . . . . . . . . . . . . . . . . . . . 14
6. Join/Prune Processing . . . . . . . . . . . . . . . . . . . . 18
7. Outgoing Interface List Explicit Tracking . . . . . . . . . . 19
8. Multiple Instances and Address-Family Support . . . . . . . . 20
9. Miscellany . . . . . . . . . . . . . . . . . . . . . . . . . . 21
10. Security Considerations . . . . . . . . . . . . . . . . . . . 22
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
13.1. Normative References . . . . . . . . . . . . . . . . . . . 25
13.2. Informative References . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
Intellectual Property and Copyright Statements . . . . . . . . . . 27
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1. Introduction
The goals of this specification are:
o To create a simple incremental mechanism to provide reliable PIM
message delivery in PIM version 2.
o The reliable transport mechanism will be used for Join-Prune
message transmission only.
o Can be used for link-local transmission of Join-Prune messages or
multi-hop for use in a multicast VPN environments.
o When a router supports this specification, it need not use the
reliable transport mechanism on every interface. That is,
negotiation on per interface basis (or MDT basis) will occur.
The explicit non-goals of this specification are:
o Changes to the PIM protocol machinery as defined in [RFC4601].
The reliable transport mechanism will be used as a plugin layer so
the PIM component does not know it is really there.
o Provide support for both Datagram mode and Transport mode (see
Section 1.2 for definitions) on the same physical interface or
MDT.
This document will specify how periodic JP message transmission can
be eliminated by using TCP [RFC0761] or SCTP [RFC4960] as the
reliable transport mechanism for JP messages.
This specification enables greater scalability in multicast
deployment since the processing required for protocol state
maintenance can be reduced. These enhancements to PIMv2 are
applicable to IP multicast over routed services and VPNs [MCAST-VPN].
In addition to reduced processing on PIM enabled routers, another
important feature is the reduced join and leave latency provided
through a reliable transport.
In many existing and emerging networks, particularly wireless and
mobile satellite systems, link degradation due to weather,
interference, and other impairments can result in temporary spikes in
the packet loss. In these environments, periodic PIM joining can
cause join latency when messages are lost causing a retransmission
only 60 seconds later. By applying a reliable transport, a lost join
is retransmitted rapidly. Furthermore, when the last user leaves a
multicast group, any lost prune is similarly repaired and the
multicast stream is quickly removed from the wireless/satellite link.
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Without a reliable transport, the multicast transmission could
otherwise continue until it timed out, roughly 3 minutes later. As
network resources are at a premium in many of these environments,
rapid termination of the multicast stream is critical to maintaining
efficient use of bandwidth.
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1.1. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1.2. Definitions
PORT: Stands for PIM Over Reliable Transport. Which is the short
form for describing the mechanism in this specification where PIM
can use the TCP or SCTP transport protocol.
JP Message: An abbreviation for a Join-Prune message.
Periodic JP: A JP message sent periodically to refresh state.
Incremental JP: A JP message sent as a result of state creation or
deletion events. Also known as a triggered message.
Native JP: A JP message which is carried with an IP protocol type
of PIM.
Reliable JP: A JP message using TCP or SCTP for transport.
Datagram Mode: The current procedures PIM uses by encapsulating JP
messages in IP packets sent either triggered or periodically.
Transport Mode: Procedures used by PIM defined in this
specification for sending JP messages over the TCP or SCTP
transport layer.
MDT/PMSI: Used interchangeably in this document. An MDT tunnel is
one used between PE router to provide support for a Multicast VPN.
The new standards term for an MDT tunnel is a Provider-Network
Multicast Service Interface or PMSI.
Segmented Multi-Access LAN: A segmented (or partitioned) LAN is
like a virtual overlay network using the physical LAN to realize
control and data packets. Multiple overlay networks may be
created using the physical LAN, much like how VLANs or PMSI
overlays are configured over a multi-access phsyical LAN. The
interface associated with the partitioned LAN is like an NBMA
interface type so explicit tracking can be accomplished. Each
partitioned or segmented LAN has it's own data-link encapsulation
and link-layer multicast is still used to avoid head-end
replication. This concept also applies to MDTs/PMSIs and is
called "Segmented MDTs/PMSIs". A Segmented MDT/PMSI is a MDT/PMSI
that has a single forwarder (i.e. a single ingress PE) for any
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multicast stream.
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2. Protocol Overview
PIM Over Reliable Transport (PORT) is a simple extension to PIMv2 for
refresh reduction of PIM JP messages. It involves sending
incremental rather than periodic JPs over a TCP/SCTP connection
between PIM neighbors.
PORT can be incrementally used on an interface between PORT capable
neighbors. Routers which are not PORT capable can continue to use
PIM in Datagram Mode. PORT capability is detected using a new PORT
Capable PIM Hello Option.
When PORT is used, only incremental JPs are sent from downstream
routers to upstream routers. As such, downstream routers do not
generate periodic JPs for routes which RPF to a PORT-capable
neighbor.
For Joins and Prunes, which are received over a TCP/SCTP connection,
the upstream router does not start or maintain timers on the outgoing
interface entry. Instead, it explicitly tracks downstream routers
which have expressed interest. An interface is deleted from the
outgoing interface list only when all downstream routers on the
interface, no longer wish to receive traffic.
Because incremental JPs are sent over a TCP/SCTP connection, no Join
suppression or Prune-Override of incremental JPs is possible on
multi-access LANs. As a result, upstream routers, which receive an
incremental Join or Prune that creates state, explicitly track all
downstream nodes. Note, for point-to-point links there is no need
for explicitly tracking downstream nodes.
There is no change proposed for the PIM JP packet format. However,
for JPs sent over TCP/SCTP connections, no IP Header is included.
The message begins with the PIM common header, followed by the JP
message. See section Section 5 for details on the common header.
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3. New PIM Hello Options
3.1. PIM over the TCP Transport Protocol
Option Type: PIM-over-TCP Capable
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 65006 | Length = X + 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TCP Connection ID AFI | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TCP Connection ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Allocated Hello Type values can be found in [HELLO-OPT].
When a router is configured to use PIM over TCP on a given interface,
it MUST include the PORT Capable hello option in its Hello messages
for that interface. If a router is explicitly disabled from using JP
over TCP it MUST NOT include the PORT Capable hello option in its
Hello messages. When the router cannot setup a TCP connection, it
will refrain from including this option.
This option is only used when an interface is point-to-point,
segmented multi-access LAN or a PMSI [MCAST-VPN]. In all other
cases, such as multi-access LANs, Datagram Mode is used.
Implementation may provide a configuration option to enable or
disable PORT functionality. We recommend that this capability be
disabled by default.
Length: In bytes for the value part of the Type/Length/Value
encoding. Where X is 4 bytes if IP AFI of value 1 is used and 16
bytes when IPv6 AFI of 2 is used [AFI].
TCP Connection ID AFI: The AFI value to describe the address-family
of the address of the TCP Connection ID field.
Reserved: Set to zero on transmission and ignored on receipt.
TCP Connection ID: An IP or IPv6 address used to establish the TCP
connection. When this field is 0, a mechanism outside the scope
of this spec is used to obtain the addresses used to establish the
TCP connection.
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3.2. PIM over the SCTP Transport Protocol
Option Type: PIM-over-SCTP Capable
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 65007 | Length = X + 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SCTP Connection ID AFI | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SCTP Connection ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Allocated Hello Type values can be found in [HELLO-OPT].
When a router is configured to use PIM over SCTP on a given
interface, it MUST include the PORT Capable hello option in its Hello
messages for that interface. If a router is explicitly disabled from
using JP over SCTP it MUST NOT include the PORT Capable hello option
in its Hello messages. When the router cannot setup a SCTP
connection, it will refrain from including this option.
This option is only used when an interface is point-to-point or when
a multi-access LAN or MDT is segmented (also known as "Partitioned
MDTs" in a non-broadcast multi-access (NBMA) mode. In all other
cases, such as general purpose multi-access LANs, Datagram Mode is
used.
Implementation may provide a configuration option to enable or
disable PORT functionality. We recommend that this capability be
disabled by default.
Length: In bytes for the value part of the Type/Length/Value
encoding. Where X is 4 bytes if IP AFI of value 1 is used and 128
bytes when IPv6 AFI of 2 is used [AFI].
SCTP Connection ID AFI: The AFI value to describe the address-
family of the address of the SCTP Connection ID field.
Reserved: Set to zero on transmission and ignored on receipt.
SCTP Connection ID: An IP or IPv6 address used to establish the
SCTP connection. When this field is 0, a mechanism outside the
scope of this spec is used to obtain the addresses used to
establish the SCTP connection.
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4. Establishing Transport Connections
Since this specification describes using Transport on point-to- point
links or NBMA configured MDTs, a router knows when a Transport is
established with the neighbor. When the Transport connection is not
established, Datagram Mode is used. When the Transport connection
becomes established Transport Mode is in effect where the router can
suppress sending periodic JPs.
When a router receives a Hello from a neighbor it has not previously
heard from, or the PORT-Capable Option is included in a Hello that
was not previously included by an existing neighbor, the router will
attempt to establish a Transport connection with the neighbor. When
the router is using TCP it will compare the IP address it uses to
send Hellos on the interface with the IP address the neighbor is
using to send Hellos. The router with the lower IP address will do
an active Transport open to the neighbor address. The higher IP
addressed neighbor will do a passive Transport open. When the router
is using SCTP, the IP address comparison not be done since the SCTP
protocol can handle call collision.
When a Transport connection goes down, Join or Prune state that was
sent over the Transport connection is still retained. The neighbor
should not be considered down until the neighbor timer has expired.
This allows routers to do a control-plane switchover without
disrupting the network. If a Transport connection is reestablished
before the neighbor timer expires, the previous state is intact and
any new JP messages sent cause state to be created or removed
(depending on if it was a Join or Prune). If the neighbor timer does
expire, only the upstream router, that has oif-list state, to the
expired downstream neighbor will need to clear state. A downstream
router, when an upstream neighboring router has expired, will simply
RPF to a new neighbor where it would trigger JP messages like it
would in [RFC4601]. It is required of a PIM router to clear it's
neighbor table for a neighbor who has timed out due to neighbor
holdtime expiration.
When a router is in Datagram Mode with a neighbor and has been
sending periodic JP messages to it and then the Transport connection
has been established to the neighbor, there is no requirement for the
downstream router to send JP messages to the upstream neighbor. The
upstream router can keep the state maintained from the Datagram Mode
creation. However when a router is in Transport Mode with a neighbor
and moves to Datagram Mode because the transport connection went down
(and several attempts to reestablish the transport connection fail),
the router cannot be sure that all the JP data was received by the
neighbor. Therefore, it is required to send a full set of JP
messages to refresh or re-create state in the upstream neighbor.
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An upstream neighbor does have the responsibility of removing the
timer-activated timeout of an oif-list entry. When a Transport
connection is established, the timer-activated timeout is disabled.
When a Transport connection goes down, the timer-activated timeout
for an oif-list is enabled. Both the upstream and downstream routers
stay in sync based on the state of the Transport connection. If the
upstream router has timer-activated timeout on oif-lists, the
downstream router will be sending periodic JPs. Otherwise, the
downstream router suppresses sending periodic JPs because it assumes
the upstream router has disabled the timer-activated timeout of oif-
list entries the downstream router has previously joined.
4.1. TCP Connection Maintenance
TCP is designed to keep connections up indefinitely during a period
of network disconnection. If a PIM-over-TCP router fails, the TCP
connection may stay up until the neighbor actually reboots, and even
then it may continue to stay up until you actually try to send the
neighbor some information. This is particularly relevant to PIM,
since the flow of JPs might be in only one direction, and the
downstream neighbor might never get any indication via TCP that the
other end of the connection isn't really there.
Most applications using TCP want to detect when a neighbor is no
longer there, so that the associated application state can be
released. Also, one wants to clean up the TCP state, and not keep
half-open connections around indefinitely. This is accomplished by
using PIM Hellos and by not introducing an application-specific or
new PIM keep-alive message. Therefore, when a GENID changes from a
received PIM Hello message, and a TCP connection is established or
attempting to be established, the local side will tear down the
connection and attempt to reopen a new one for the new instance of
the neighbor coming up.
When PORT capable routers come up and try to establish transport
connections with their neighbors, but cannot for some reason, after 3
attempts to do so, the router should go into datagram mode and not
advertise the PORT Hello option anymore. Operator intervention is
required to restart the process after the problem is found.
4.2. Transitional Periods
There may be transitional periods when a router receives, from a
given neighbor, both datagram JP messages and JP messages sent over a
transport connection. When this happens, a transport connection to a
particular neighbor is established, and as long as it remains
established, the router MUST ignore PIM messages sent in Datagram
Mode from that neighbor. Otherwise, the datagram messages could get
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out of order with respect to the transport messages, and the router
could end up in an erroneous state of pruning joined state or joining
pruned state which it is unable to recover from as long as the
transport connection stays up.
4.3. On-demand versus Pre-configured Connections
Transport connections could be established when they are needed or
when a router interface to other PIM neighbors has come up. The
advantages of on-demand Transport connection establishment are the
reduction of router resources. Especially in the case where there is
no need for n^2 connections on a network interface or MDT tunnel.
The disadvantages are deciding what to do when a JP message needs to
be sent and a Transport connection is not established yet. An
implementation can either send a Datagram Mode JP or queue the JP to
be sent as a Transport Mode JP after the Transport connection is
established.
If a router interface has become operational and PIM neighbors are
learned from Hello messages, at that time, Transport connections may
be established. The advantage is that a connection is ready to
transport data by the time a JP messages needs to be sent. The
disadvantage is there can be more connections established than
needed. This can occur when there is a small set of RPF neighbors
for the active distribution trees compared to the total number of
neighbors. Even when Transport connections are pre-established
before they are needed, a connection can go down and an
implementation will have to deal with an on-demand situation.
Therefore, this specification recommends but does not mandate the use
of on-demand Transport connection establishment.
4.4. Possible Hello Suppression Considerations
This specification indicates that a Transport connection cannot be
established until a Hello message is received. One reason for this
is to determine if the PIM neighbor supports this specification and
the other is to determine the remote address to use to establish the
Transport connection.
There are cases where it is desirable to suppress entirely the
transmission of Hello messages. In this case, it is outside the
scope of this document on how to determine if the PIM neighbor
supports this specification as well as an out-of-band (outside of the
PIM protocol) method to determine the remote address to establish the
Transport connection.
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4.5. Avoiding a Pair of Connections between Neighbors
To ensure there are not two connections between a pair of PIM
neighbors, the following set of rules must be followed. Let A and B
be two PIM neighbors where A's IP address is numerically smaller than
B's IP address, and each is known to the other as having a potential
PIM adjacency relationship.
At node A:
o If there is already an established TCP connection to B, on the
PIM-over-TCP port, then A MUST NOT attempt to establish a new
connection to B. Rather it uses the established connection to send
JPs to B. (This is independent of which node initiated the
connection.)
o If A has initiated a connection to B, but the connection is still
in the process of being established, then A MUST refuse any
connection on the PIM-over-TCP port from B.
o At any time when A does not have a connection to B which is either
established or in the process of being established, A MUST accept
connections from B.
At node B:
o If there is already an established TCP connection to A, on the
PIM-over-TCP port, then B MUST NOT attempt to establish a new
connection to A. Rather it uses the established connection to send
JPs to A. (This is independent of which node initiated the
connection.)
o If B has initiated a connection to A, but the connection is still
in the process of being established, then if A initiates a
connection to, B MUST accept the connection initiated by A and
must release the connection which it (B) initiated.
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5. Common Header Definition
It may be desirable for scaling purposes to include JP messages from
different PIM protocol instances to be sent over the same Transport
connection. Also, it may be desirable to have a set of JP messages
for one address-family sent over a Transport connection that is
established over a different address-family network layer.
To be able to do this we need a common header that is inserted and
parsed for each PIM JP message that is sent on a Transport
connection. This common header will provide both record boundary and
demux points when sending over a stream protocol like Transport.
Each JP message will have in front of it the following common header
in Type/Length/Value format. And multiple different TLV types can be
sent over the same Transport connection.
To make sure PIM JP messages are delivered as soon as the TCP
transport layer receives the JP buffer, the TCP Push flag will be set
in all outgoing JP messages sent over a TCP transport connection.
PIM messages will be sent using TCP port number TBD. When using SCTP
as the reliable transport, port number TBD will be used. See
Section 11 for IANA considerations.
If the buffer length of the received TLV message is less than what is
encoded in the TLV Length field, the entire TLV encoded message is
ignored and a error message is logged. Likewise, if the received
buffer length left to process at each record parsing level, is less
than the JP Message Length, the rest of the message is malformed and
not processed.
Each JP message that has passed the length checks above, contained in
the TLV encoding, will be error checked individually. This includes
a bad PIM checksum, illegal type fields, or illegal addresses. If
any parsing errors occur in a single JP message, it is skipped over
and not processed but other JP message records in the TLV are still
parsed and processed.
The current list of defined TLVs are:
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IPv4 JP Message
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1 | Length = (12 * X) + Y |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| JP Message Length | Reserved |I-Type|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Instance ID . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . Instance ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PIMv2 JP Message |
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| JP Message Length | Reserved |I-Type|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Instance ID . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . Instance ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PIMv2 JP Message |
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The IPv4 JP common header is used when a JP message is sent that has
all IPv4 encoded addresses in the PIM payload.
Length: In bytes for the value part of the Type/Length/Value
encoding. Where there are 12 bytes per JP message (where X above
is the number of JP messages contained) enclosed in one
transmission plus Y which is the sum of each "JP Message Length"
field that appears in the transmission.
I-Type: Defines the encoding and semantics of the Instance ID
field. This is not specified in this specification.
Instance ID: This can be a VPN-ID. This field could also be a BGP
Route Target (RT) or BGP Route Distinguisher (RD) as defined in
[RFC4364]. Not specified in this specification.
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Reserved: Set to zero on transmission and ignored on receipt.
JP Message Length: The number of bytes that follow which make up
the PIMv2 JP message.
PIMv2 JP Message: PIMv2 Join/Prune message and payload with no IP
header in front of it. As you can see from the packet format
diagram, multiple JP messages can go into one TCP/SCTP stream from
the same or different Instance IDs.
IPv6 JP Message
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Length = (12 * X) + Y |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| JP Message Length | Reserved |I-Type|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Instance ID . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . Instance ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PIMv2 JP Message |
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| JP Message Length | Reserved |I-Type|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Instance ID . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . Instance ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PIMv2 JP Message |
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The IPv6 JP common header is used when a JP message is sent that has
all IPv6 encoded addresses in the PIM payload.
Length: In bytes for the value part of the Type/Length/Value
encoding. Where there are 12 bytes per JP message (where X above
is the number of JP messages contained) enclosed in one
transmission plus Y which is the sum of each "JP Message Length"
field that appears in the transmission.
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I-Type: Defines the encoding and semantics of the Instance ID
field. This is not specified in this specification.
Instance ID: This can be a VPN-ID, BGP Route Target (RT) or BGP
Route Distinguisher (RD). Not specified in this specification.
Reserved: Set to zero on transmission and ignored on receipt.
JP Message Length: The number of bytes that follow which make up
the PIMv2 JP message.
PIMv2 JP Message: PIMv2 Join/Prune message and payload with no IP
header in front of it. As you can see from the packet format
diagram, multiple JP messages can go into one TCP/SCTP stream from
the same or different Instance IDs.
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6. Join/Prune Processing
When a PORT neighbor transitions to using Transport Mode, the
downstream router sends JP messages for existing routes that RPF to
the neighbor over the Transport connection. In addition, periodic JP
messages are stopped and only incremental JPs are sent thereafter.
A router which has a Transport connection established MUST send and
receive JP messages over the Transport session to that given peer as
well as accept and process native JP messages as described in
[RFC4601].
When a Transport connection is established for a newly discovered
neighbor, the downstream router triggers JP messages for its existing
state. This is to allow the upstream router to build state it may
previously not had. If state had existed due to a Native JP, the
expiration timer would have been started. Now it can be stopped
because the state is being sent incrementally over the Transport
connection.
When a Transport connection goes down to a given neighbor, the
downstream router does not have to trigger native JP messages. It
can wait for its next periodic interval to send a native JP messages.
When the upstream router receives the native JP message, it will
start the expiration timer for the oif associated with the state from
the JP message.
Note, since JP messages are sent over a Transport connection, no
Prune Override or Join Suppression are possible for these messages.
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7. Outgoing Interface List Explicit Tracking
Since this specification indicates the use of TCP/SCTP for PIM JP
messages over point-to-point or NBMA type links, explicit tracking
can be achieved by tracking only oif-list state and not per-neighbor
per oif-list state. This is true for segmented LANs and in segmented
MDT/PMSI environments.
By using explicit tracking of oifs, the router tracks all downstream
neighbors which have expressed interest in a route on a given
interface. The list of tracked routers is one of the checks used to
determine whether traffic needs to be forwarded on a given interface
or not.
For (*,G) and (S,G) routes, the router starts forwarding traffic on
an interface when a Join is received from a neighbor on such an
interface. This is tracking the oif to the neighbor. When the
neighbor sends a Prune, the interface is removed and forwarding of
traffic stops on the interface.
When all interfaces are removed from the oif-list, the route entry
can be removed.
For (S,G,R) routes, typically is tracking Prune state on the shared
tree. One at least one downstream neighbor sends a Prune over a
Transport connection, the (S,G,R) state is create with a empty
outgoing interface list. If a subsequent JP is received over a
Transport connection which has (*,G) in the join-list and does not
have (S,G,R) in the prune-list, the upstream router will add the
interface the JP message was received on to the oif-list. And oif-
list based explicit tracking will occur just like in the (*,G) and
(S,G) route case above.
The only difference in the (S,G,R) route case, is that when the
outgoing interface is pruned, the entry must stay in the route table
or else forwarding will occur on the interfaces for the (*,G) entry.
Therefore, explicit tracking for Prunes must be provided. Only when
the (S,G,R) oif-list interfaces match the interfaces in the (*,G) can
the (S,G,R) route be removed.
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8. Multiple Instances and Address-Family Support
Multiple instances of the PIM protocol may be used to support
multiple VPNs or within a VPN to support multiple address families.
Multiple instances can cause a multiplier effect on the number of
router resources consumed. To be able to have an option to use
router resources more efficiently, muxing JP messages over fewer
Transport connections can be performed.
There are two ways this can be accomplished, one using a common
header format over a TCP connection and the other using multiple
streams over a single SCTP connection.
Using the Common Header format described previously in this
specification, using different TLVs, both IPv4 and IPv6 based JP
messages can be encoded within a Transport connection. Likewise,
within a TLV, multiple occurrences of JP messages can occur and are
tagged with an instance-ID so multiple JP messages for different VPNs
can use a single Transport connection.
When using SCTP multi-streaming, the common header is still used to
convey instance information but an SCTP association is used, on a
per-VPN basis, to send data concurrently for multiple instances.
When data is sent concurrently, head of line blocking, which can
occur when using TCP, is avoided.
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9. Miscellany
No changes expected in processing of other PIM messages like PIM
Asserts, Grafts, Graft-Acks, Registers, and Register-Stops. This
goes for BSR and Auto-RP type messages as well.
This extension is applicable only to PIM-SM, PIM-SSM and Bidir-PIM.
It does not take requirements for PIM-DM into consideration.
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10. Security Considerations
Transport connections can be authenticated using HMACs MD5 and SHA-1
similar to use in BGP [RFC4271] and MSDP [RFC3618].
When using SCTP as the transport protocol, [RFC4895] can be used, on
a per SCTP association basis to authenticate PIM data.
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11. IANA Considerations
This specification requests IANA to allocate a TCP port number and a
SCTP port number for the use of PIM-Over-Reliable-Transport.
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12. Acknowledgments
The authors would like to give a special thank you and appreciation
to Nidhi Bhaskar for her initial design and early prototype of this
idea.
Appreciation goes to Randall Stewart for his authoritative review and
recommendation for using SCTP.
Thanks also goes to the following for their ideas and commentary
review of this specification, Mike McBride, Toerless Eckert, Yiqun
Cai, Albert Tian, Suresh Boddapati, Nataraj Batchu, Daniel Voce, John
Zwiebel, Yakov Rekhter, and Lenny Giuliano.
A special thank you goes to Eric Rosen for his very detailed review
and commentary. Many of his comments are reflected as text in this
specification.
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13. References
13.1. Normative References
[RFC0761] Postel, J., "DoD standard Transmission Control Protocol",
RFC 761, January 1980.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3618] Fenner, B. and D. Meyer, "Multicast Source Discovery
Protocol (MSDP)", RFC 3618, October 2003.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[RFC4895] Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
"Authenticated Chunks for the Stream Control Transmission
Protocol (SCTP)", RFC 4895, August 2007.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol",
RFC 4960, September 2007.
13.2. Informative References
[AFI] IANA, "Address Family Indicators (AFIs)", ADDRESS FAMILY
NUMBERS http://www.iana.org/numbers.html, February 2007.
[HELLO-OPT]
IANA, "PIM Hello Options", PIM-HELLO-OPTIONS per
RFC4601 http://www.iana.org/assignments/pim-hello-options,
March 2007.
[MCAST-VPN]
Rosen and Aggarwal, "Multicast in MPLS/BGP VPNs", Internet
Draft draft-ietf-l3vpn-2547bis-mcast-05.txt, July 2007.
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Authors' Addresses
Dino Farinacci
cisco Systems
Tasman Drive
San Jose, CA 95134
USA
Email: dino@cisco.com
IJsbrand Wijnands
cisco Systems
Tasman Drive
San Jose, CA 95134
USA
Email: ice@cisco.com
Apoorva Karan
cisco Systems
170 Tasman Drive
San Jose, CA
USA
Email: apoorva@cisco.com
Arjen Boers
cisco Systems
Tasman Drive
San Jose, CA 95134
USA
Email: aboers@cisco.com
Maria Napierala
AT&T Labs
200 Laurel Drive
Middletown, New Jersey 07748>
USA
Email: mnapierala@att.com
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