Network Working Group D. Farinacci
Internet-Draft IJ. Wijnands
Intended status: Experimental S. Venaas
Expires: April 29, 2010 cisco Systems
M. Napierala
AT&T Labs
October 26, 2009
A Reliable Transport Mechanism for PIM
draft-ietf-pim-port-02.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 . . . . . . . . . . . . . . . . . . . . . . 6
3. New PIM Hello Options . . . . . . . . . . . . . . . . . . . . 7
3.1. PIM over the TCP Transport Protocol . . . . . . . . . . . 7
3.2. PIM over the SCTP Transport Protocol . . . . . . . . . . . 8
4. Establishing Transport Connections . . . . . . . . . . . . . . 10
4.1. TCP Connection Maintenance . . . . . . . . . . . . . . . . 11
4.2. Moving from PORT to Datagram Mode . . . . . . . . . . . . 12
4.3. On-demand versus Pre-configured Connections . . . . . . . 12
4.4. Possible Hello Suppression Considerations . . . . . . . . 13
4.5. Avoiding a Pair of Connections between Neighbors . . . . . 13
5. Common Header Definition . . . . . . . . . . . . . . . . . . . 15
6. Explicit Tracking . . . . . . . . . . . . . . . . . . . . . . 19
7. Multiple Instances and Address-Family Support . . . . . . . . 20
8. Miscellany . . . . . . . . . . . . . . . . . . . . . . . . . . 21
9. Security Considerations . . . . . . . . . . . . . . . . . . . 22
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 24
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
13.1. Normative References . . . . . . . . . . . . . . . . . . . 26
13.2. Informative References . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 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 with every neighbor. That is,
negotiation on a per neighbor 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 automatic switching between Datagram mode and
Transport mode. Two routers that are PIM neighbors on a link will
always use Transport mode if and only if both have Transport mode
enabled.
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. 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.
Without a reliable transport, the multicast transmission could
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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.
PORT Mode: Procedures used by PIM defined in this specification for
sending JP messages over the TCP or SCTP transport layer.
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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.
This document does not restrict PORT to any specific link types. It
is however not recommended to use PORT on e.g. multi-access LANs with
many PIM neighbors. This due to the fact that there may be a full
mesh of PORT connections, and that there is no join suppression.
PORT can be incrementally used on a link between PORT capable
neighbors. Routers which are not PORT capable can continue to use
PIM in Datagram Mode. PORT capability is detected using new PORT
Capable PIM Hello Options.
Once PORT is enabled on an interface and a PIM neighbor also
announces that it is PORT enabled, only Reliable JP messages will be
used. That is, only Reliable JP messages are accepted from, and sent
to, that particular neighbor. Native JP messages may still be used
for other neighbors.
Reliable JP messages are sent using a TCP/SCTP connection. When two
PIM neighbors are PORT enabled, both for TCP or both for SCTP, they
will immediately, or on-demand, establish a connection. If the
connection goes down, they will again immediately, or on-demand, try
to reestablish the connection. No JP messages (neither Native nor
Reliable) are sent while there is no connection.
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 keeps track of which downstream routers
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.
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 = 27 | Length = X + 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TCP Connection ID AFI | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TCP Connection ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface 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 PIM-over-TCP 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 PIM-over-TCP Capable hello
option in its Hello messages. When the router cannot setup a TCP
connection, it will refrain from including this option.
Implementations 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 AFI of value 1 (IPv4) is used and
16 bytes when AFI of value 2 (IPv6) is used [AFI].
TCP Connection ID AFI: The AFI value to describe the address-family
of the address of the TCP Connection ID field. 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.
Reserved: Set to zero on transmission and ignored on receipt.
TCP Connection ID: An IPv4 or IPv6 address used to establish the
TCP connection. This field is omitted (length 0) for the
Connection ID AFI 0.
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Interface ID: An Interface ID is used to associate the connection a
JP message is received over with an interface which is added or
removed from an oif-list. When unnumbered interfaces are used or
when a single Transport connection is used for sending and
receiving JP messages over multiple interfaces, the Interface ID
is used convey the interface from JP message sender to JP message
receiver. When a PIM router sets a locally generated value for
the Interface ID in the Hello TLV, it must send the same Interface
ID value in all JP messages it is sending to the PIM neighbor.
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 = 28 | Length = X + 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SCTP Connection ID AFI | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SCTP Connection ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface 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 PIM-over-SCTP 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 PIM-over-
SCTP Capable hello option in its Hello messages. When the router
cannot setup a SCTP connection, it will refrain from including this
option.
Implementations 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 AFI of value 1 (IPv4) is used and
16 bytes when AFI of value 2 (IPv6) is used [AFI].
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SCTP Connection ID AFI: The AFI value to describe the address-
family of the address of the SCTP Connection ID field. 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.
Reserved: Set to zero on transmission and ignored on receipt.
SCTP Connection ID: An IPv4 or IPv6 address used to establish the
SCTP connection. This field is omitted (length 0) for the
Connection ID AFI 0.
Interface ID: An Interface ID is used to associate the connection a
JP message is received over with an interface which is added or
removed from an oif-list. When unnumbered interfaces are used or
when a single Transport connection is used for sending and
receiving JP messages over multiple interfaces, the Interface ID
is used convey the interface from JP message sender to JP message
receiver. When a PIM router sets a locally generated value for
the Interface ID in the Hello TLV, it must send the same Interface
ID value in all JP messages it is sending to the PIM neighbor.
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4. Establishing Transport Connections
While a router interface is PORT enabled, a PIM-over-TCP or a PIM-
over-SCTP option is included in the PIM Hello messages sent on that
interface. When a router on a PORT-enabled interface receives a
Hello message containing a PIM-over-TCP/PIM-over-SCTP Option from a
new neighbor, or an existing neighbor that did not previously include
the option, it switches to PORT mode for that particular neighbor.
When a router switches to PORT mode for a neighbor, it stops sending
and accepting Native JP messages for that neighbor. Any state from
previous Native JP messages is left to expire as normal. It will
also attempt to establish a Transport connection (TCP or SCTP) with
the neighbor.
When the router is using TCP it will compare the TCP Connection ID it
announced in the PIM-over-TCP Capable Option with the TCP Connection
ID in the Hello received from the neighbor. The router with the
lower Connection ID will do an active Transport open to the neighbor
Connection ID. The router with the higher Connection ID will do a
passive Transport open. An implementation may open connections only
on-demand, in that case it may be that the neighbor with the higher
Connection ID does the active open, see Section 4.3. Note that the
source address of the active open must be the announced Connection
ID.
When the router is using SCTP, the IP address comparison need not be
done since the SCTP protocol can handle call collision.
If PORT is used both for IPv4 and IPv6, both IPv4 and IPv6 PIM Hello
messages are sent, both containing PORT Hello options. If two
neighbors announce the same transport (TCP or SCTP) and the same
Connection ID in the IPv4 and IPv6 Hello messages, then only one
connection is established and is shared. Otherwise, two connections
are established and are used separately.
The PIM router that performs the active open initiates the connection
with a locally generated source transport port number and a well-
known destination transport port number. The PIM router that
performs the passive open listens on the well-known local transport
port number and does not qualify the remote transport port number.
See Section 5 for well-known port number assignment for PORT.
When a Transport connection is established (or reestablished), the
two routers MUST both send a full set of JP messages for which the
other router is the upstream neighbor. This is needed to ensure that
the upstream neighbor has the correct state. When moving from
Datagram mode, or when the connection has gone down, the router
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cannot be sure that all the previous JP data was received by the
neighbor. Any state received while in Datagram mode that is not
refreshed, will be left to expire.
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 its
neighbor table for a neighbor who has timed out due to neighbor
holdtime expiration.
Note, since JP messages are sent over a Transport connection, no
Prune Override or Join Suppression are possible for these messages.
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. However, if the connection is shared by
multiple interfaces and the GENID changes only for one of them, then
there was not a full reboot and the connection is likely to still
work. In that case, the router should just resend all JP state for
that particular neighbor. This is similar to how state is refreshed
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when GENID changes for PIM in datagram mode.
There may be situations where a router ignores some joins or prunes.
E.g. due to wrong RP information or receiving joins on an RPF
interface. A router may try to cache such messages and apply them
later if only a temporary error. It may however also ignore the
message, and later change its GENID for that interface to make the
neighbor resend all state, including any that may have been
previously ignored. It is possible that one receives JP messages for
an interface/link that is down. As long as the neighbor has not
expired, we recommend processing those messages as usual. If they
are ignored, then the router should change the GENID for that
interface when it comes back up, in order to get a full update.
4.2. Moving from PORT to Datagram Mode
There may be situations where an administrator decides to stop using
PORT. If PORT is disabled on a router interface, we start expiry
timers with the respective neighbor holdtimes as the initial values.
Similarly if we receive a Hello message without a PORT Capable option
from a neighbor, we start expiry timers for all JP state we have for
that particular neighbor. The Transport connection should be shut
down as soon as there are no more PIM neighborships using it. That
is, for the connection we have associated local and remote Connection
IDs. When there is no PIM neighbor with that particular remote
connection ID on any interface where we announce the local connection
ID, the connection should be shut down.
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
advantage of on-demand Transport connection establishment is 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 disadvantage is additional delay and queueing when a JP message
needs to be sent and a Transport connection is not established yet.
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.
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Note that for TCP, it is the router with the lower Connection ID that
decides whether to open a connection immediately, or on-demand. The
router with the higher Connection ID should only initiate a
connection on-demand. That is, if it needs to send a JP message and
there is no currently established connection.
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.
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 Connection ID is numerically smaller
than B's Connection ID, 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.
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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 too, 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 allow 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 destination TCP port number 8471.
When using SCTP as the reliable transport, destination port number
8471 will be used. See Section 10 for IANA considerations.
JP messages are error checked. This includes a bad PIM checksum,
illegal type fields, illegal addresses or a truncated message. If
any parsing errors occur in a JP message, it is skipped, and we
proceed processing any following TLVs.
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 = X + 16 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |I-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 X is the number of bytes that make up the PIMv2
JP message.
I-Type: Defines the encoding and semantics of the Instance ID
field. Instance Type 0 means Instance ID is not used. Other
values are not defined in this specification.
Interface ID: This is the Interface ID from the Hello TLV, defined
in this specification, the PIM router is sending to the PIM
neighbor. It indicates to the PIM neighbor what interface to
associate the JP Join or Prune with.
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]. This document only defines this for Instance Type 0.
For type 0 the field should be set to zero on transmission and
ignored on receipt.
Reserved: Set to zero on transmission and ignored on receipt.
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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 Interface and 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 = X + 16 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |I-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 X is the number of bytes that make up the PIMv2
JP message.
I-Type: Defines the encoding and semantics of the Instance ID
field. Instance Type 0 means Instance ID is not used. Other
values are not defined in this specification.
Interface ID: This is the Interface ID from the Hello TLV, defined
in this specification, the PIM router is sending to the PIM
neighbor. It indicates to the PIM neighbor what interface to
associate the JP Join or Prune with.
Instance ID: This can be a VPN-ID, BGP Route Target (RT) or BGP
Route Distinguisher (RD). This document only defines this for
Instance Type 0. For type 0 the field should be set to zero on
transmission and ignored on receipt.
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Reserved: Set to zero on transmission and ignored on receipt.
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 Interface and Instance IDs.
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6. Explicit Tracking
A router needs to keep track of which PORT neighbors express interest
in a route on a given interface. For non-PORT neighbors, there is no
change, one would usually just need to know if at least one non-PORT
neighbor is interested. For some link-types, e.g. point-to-point,
tracking neighbors is no different than tracking interfaces. It may
also be possible for an implementation to treat different downstream
neighbors as being on different logical interfaces, even if they are
on the same physical link. Exactly how this is implemented and for
which link types, is left to the implementer.
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. When a non-PORT neighbor sends a Prune, there is
generally a small delay to see if another non-PORT neighbor sends a
Prune Override. If there is no override, one should note that no
non-PORT neighbor is interested. If no PORT neighbors are
interested, the interface can be removed from the oif-list. When a
PORT neighbor sends a Prune, one removes the join state for that
neighbor. If no other PORT or non-PORT neighbors are interested, the
interface can be removed from the oif-list. In this case there is no
Prune Override, since the Prune was not visible to other neighbors.
For (S,G,R) routes, the router needs to track Prune state on the
shared tree. It needs to know which PORT neighbors have sent prunes,
and whether any non-PORT neighbors have sent prunes. The latter is
exactly like when not using PORT. Normally one would forward a
packet from a source S to a group G out on an interface if a
(*,G)-join is received, but no (S,G,R)-prune. With PORT one needs to
do this check per PORT neighbor. That is, the packet should be
forwarded unless all PORT neighbors that have sent (*,G)-joins have
also sent (S,G,R)-prunes and if a non-PORT neighbor has sent a
(*,G)-join, whether there also is non-PORT (S,G,R)-prune state.
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7. 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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8. 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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9. 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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10. IANA Considerations
This specification makes use of a TCP port number and a SCTP port
number for the use of PIM-Over-Reliable-Transport that has been
allocated by IANA. It also makes use of IANA PIM Hello Options
allocations that should be made permanent. In addition, a registry
for PORT message types is requested. This document defines two PORT
message types. Type 1, IPv4 JP Message; and Type 2, IPv6 JP Message.
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11. Contributors
In addition to the persons listed as authors, significant
contributions were provided by Apoorva Karan and Arjen Boers.
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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, Lenny Giuliano, Gorry Fairhurst and Sameer
Gulrajani.
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.
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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
Stig Venaas
cisco Systems
Tasman Drive
San Jose, CA 95134
USA
Email: stig@cisco.com
Maria Napierala
AT&T Labs
200 Laurel Drive
Middletown, New Jersey 07748>
USA
Email: mnapierala@att.com
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