Network Working Group D. Farinacci
Internet-Draft IJ. Wijnands
Intended status: Experimental S. Venaas
Expires: August 19, 2011 cisco Systems
M. Napierala
AT&T Labs
February 15, 2011
A Reliable Transport Mechanism for PIM
draft-ietf-pim-port-05.txt
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.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 19, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 5
1.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
3. PIM Hello Options . . . . . . . . . . . . . . . . . . . . . . 8
3.1. PIM over the TCP Transport Protocol . . . . . . . . . . . 8
3.2. PIM over the SCTP Transport Protocol . . . . . . . . . . . 9
3.3. Interface ID . . . . . . . . . . . . . . . . . . . . . . . 10
4. Establishing Transport Connections . . . . . . . . . . . . . . 11
4.1. Connection Security . . . . . . . . . . . . . . . . . . . 12
4.2. Connection Maintenance . . . . . . . . . . . . . . . . . . 13
4.3. Actions When a Connection Goes Down . . . . . . . . . . . 14
4.4. Moving from PORT to Datagram Mode . . . . . . . . . . . . 15
4.5. On-demand versus Pre-configured Connections . . . . . . . 15
4.6. Possible Hello Suppression Considerations . . . . . . . . 16
4.7. Avoiding a Pair of TCP Connections between Neighbors . . . 16
5. PORT Message Definition . . . . . . . . . . . . . . . . . . . 18
5.1. PORT Join/Prune Message . . . . . . . . . . . . . . . . . 19
5.2. PORT Keep-alive Message . . . . . . . . . . . . . . . . . 20
5.3. PORT Options . . . . . . . . . . . . . . . . . . . . . . . 21
6. Explicit Tracking . . . . . . . . . . . . . . . . . . . . . . 23
7. Multiple Address-Family Support . . . . . . . . . . . . . . . 24
8. Miscellany . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9. Security Considerations . . . . . . . . . . . . . . . . . . . 26
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
10.1. PORT Message Type Registry . . . . . . . . . . . . . . . . 27
10.2. PORT Option Type Registry . . . . . . . . . . . . . . . . 27
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 28
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
13.1. Normative References . . . . . . . . . . . . . . . . . . . 30
13.2. Informative References . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32
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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 for use with PIM Sparse-Mode
[RFC4601] (including Source-Specific Multicast) and Bidirectional
PIM [RFC5015].
o The reliable transport mechanism will be used for Join-Prune
message transmission only.
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 message formats as defined in [RFC4601].
o Provide support for automatic switching between the reliable
transport mechanism and the regular PIM mechanism defined in
[RFC4601]. Two routers that are PIM neighbors on a link will
always use the reliable transport mechanism if and only if both
have reliable transport enabled.
This document will specify how periodic Join/Prune message
transmission can be eliminated by using TCP [RFC0793] or SCTP
[RFC4960] as the reliable transport mechanism for Join/Prune
messages.
This specification enables greater scalability in terms of control
traffic overhead. However, for routers connected to multi-access
links that comes at the price of increased control plane state
overhead and the control plane overhead required to maintain this
state.
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
otherwise continue until it timed out, roughly 3 minutes later. As
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network resources are at a premium in many of these environments,
rapid termination of the multicast stream is critical for 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.
Periodic Join/Prune message: A Join/Prune message sent periodically
to refresh state.
Incremental Join/Prune message: A Join/Prune message sent as a
result of state creation or deletion events. Also known as a
triggered message.
Native Join/Prune message: A Join/Prune message which is carried
with an IP protocol type of PIM.
PORT Join/Prune message: A Join/Prune message using TCP or SCTP for
transport.
Datagram Mode: The current procedures PIM uses by encapsulating
Join/Prune messages in IP packets sent either triggered or
periodically.
PORT Mode: Procedures used by PIM defined in this specification for
sending Join/Prune 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 Join/Prune messages. It involves sending
incremental rather than periodic Join/Prune messages over a TCP/SCTP
connection between PIM neighbors.
PORT only applies to PIM Sparse-Mode [RFC4601] and Bidirectional PIM
[RFC5015] Join/Prune messages.
This document does not restrict PORT to any specific link types.
However, the use of PORT on e.g. multi-access LANs with many PIM
neighbors should be carefully evaluated. This due to the fact that
there may be a full mesh of PORT connections, and that explicit
tracking of all PIM PORT routers is required.
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 PORT Join/Prune messages will
be used. That is, only PORT Join/Prune messages are accepted from,
and sent to, that particular neighbor. Native Join/Prune messages
are still used for PIM neighbors that are not PORT enabled.
PORT Join/Prune 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 Join/Prune messages (neither
Native nor PORT) are sent while there is no connection. Also, any
received native Join/Prune messages from that neighbor are discarded,
even when the connection is down.
When PORT is used, only incremental Join/Prune messages are sent from
downstream routers to upstream routers. As such, downstream routers
do not generate periodic Join/Prune messages for state for which the
RPF neighbor is PORT-capable.
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. If there also are native joins/
prunes from non-PORT neighbor, then one can maintain timers on the
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outgoing interface entry as usual, while at the same time keep track
of each of the downstream PORT joins/prunes.
There is no change proposed for the PIM Join/Prune packet format.
However, for Join/Prune messages sent over TCP/SCTP connections, no
IP Header is included. Each message is contained in a PORT message.
See section Section 5 for details on the PORT message.
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3. 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 = 4 + X |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TCP Connection ID AFI | Reserved | Exp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 PIM-over-TCP Capable hello option in its Hello
messages for that interface. If a router is explicitly disabled from
using PIM over TCP, it MUST NOT include the PIM-over-TCP Capable
hello option in its Hello messages.
All Hello messages containing the PIM-over-TCP Capable hello option,
MUST also contain the Interface ID hello option, see section .
Implementations MAY provide a configuration option to enable or
disable PORT functionality. We RECOMMEND that this capability be
disabled by default.
Length: Length in bytes for the value part of the Type/Length/Value
encoding; where X is the number of bytes that make up the
Connection ID field. X is 4 when AFI of value 1 (IPv4) is used,
16 when AFI of value 2 (IPv6) is used, and 0 if AFI of value 0 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 document is used to
obtain the addresses used to establish the TCP connection.
Reserved: Set to zero on transmission and ignored on receipt.
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Exp: For experimental use [RFC3692].
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.
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 = 4 + X |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SCTP Connection ID AFI | Reserved | Exp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 PIM-over-SCTP Capable hello option in
its Hello messages for that interface. If a router is explicitly
disabled from using PIM over SCTP, it MUST NOT include the PIM-over-
SCTP Capable hello option in its Hello messages.
All Hello messages containing the PIM-over-SCTP Capable hello option,
MUST also contain the Interface ID hello option, see section .
Implementations MAY provide a configuration option to enable or
disable PORT functionality. We RECOMMEND that this capability be
disabled by default.
Length: Length in bytes for the value part of the Type/Length/Value
encoding; where X is the number of bytes that make up the
Connection ID field. X is 4 when AFI of value 1 (IPv4) is used,
16 when AFI of value 2 (IPv6) is used, and 0 if AFI of value 0 is
used [AFI].
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 document is used
to obtain the addresses used to establish the SCTP connection.
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Reserved: Set to zero on transmission and ignored on receipt.
Exp: For experimental use [RFC3692].
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.
3.3. Interface ID
All Hello messages containing PIM-over-TCP Capable or PIM-over-SCTP
Capable hello options, MUST also contain the Interface ID hello
option [I-D.gulrajani-pim-hello-intid].
The Interface ID is used to associate the connection a Join/Prune
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 Join/
Prune messages over multiple interfaces, the Interface ID is used to
convey the interface from Join/Prune message sender to Join/Prune
message receiver. The value of the Interface ID hello option in
Hellos sent on an interface, must be the same as the Interface ID
value in all PORT Join/Prune messages sent to a PIM neighbor on that
interface.
The Interface ID need only uniquely identify an interface of a
router, it does not need to identify which router the interface
belongs to. This means that the Router ID part of the Interface ID
MAY be 0. For details on the Router ID and the value 0, see
[I-D.gulrajani-pim-hello-intid].
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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 Join/Prune messages for that neighbor. Any
state from previous Native Join/Prune messages is left to expire as
normal. It will also attempt to establish a Transport connection
(TCP or SCTP) with the neighbor. If both the router and its neighbor
have announced both PIM-over-TCP and PIM-over-SCTP options, SCTP MUST
be used.
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 4.5.
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 Join/Prune messages for
state for which the other router is the upstream neighbor. This is
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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 cannot be sure that all the previous Join/Prune state was
received by the neighbor. Any state received while in Datagram mode
that is not refreshed, will be left to expire.
It is possible that a router starts sending Hello messages with a new
Connection ID, e.g. due to configuration changes. One MUST always
use the last announced and last seen Connection IDs. When a
Connection ID changes, if the previously used connection is not
needed (there are no other PIM neighborships using the same pair of
Connection IDs), both peers MUST attempt a graceful shutdown of the
connection. Next (even if the old connection is still needed), they
MUST, unless a connection already exists with the new Connection IDs,
immediately or on-demand attempt to establish a new connection with
the new Connection IDs.
Normally the Interface ID would not change while a connection is up.
However, if it does, it should not affect the connection. It just
means that when subsequent PORT join/prune messages are received,
they should be matched against the last seen Interface ID.
Note that, a Join sent over a Transport connection will only be seen
by the upstream router, and thus will not cause routers on the link
that do not use PIM PORT with the upstream router to possibly delay
the refresh of Join state for the same state. Similarly, a Prune
sent over a Transport connection will only be seen by the upstream
router, and will thus never cause routers on the link that do not use
PIM PORT with the upstream router, to send a Join to override this
Prune.
Note also, that a datagram PIM Join/Prune message for a said (S,G) or
(*,G) sent by some router on a link will not cause routers on the
same link that use a Transport connection with the upstream router
for that state, to suppress the refresh of that state to the upstream
router (because they don't need to periodically refresh this state)
or to send a Join to override a Prune (as the upstream router will
only stop forwarding the traffic when all joined routers that use a
Transport connection have explicitly sent a Prune for this state, as
explained in Section 6).
4.1. Connection Security
TCP/SCTP packets MUST be sent with a TTL/Hop Limit of 255 to
facilitate enabling of the Generalized TTL Security Mechanism (GTSM)
[RFC5082]. Implementations SHOULD provide a configuration option to
enable the GTSM check. This means checking that inbound packets from
directly connected neighbors have a TTL/Hop Limit of 255, but MAY
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also allow for a different TTL/Hop Limit threshold to check that the
sender is within a certain number of router hops. The GTSM check
SHOULD be disabled by default.
Implementations SHOULD support the TCP Authentication Option (TCP-AO)
[RFC5925].
4.2. 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 Join/Prune messages might be in only one direction,
and the downstream neighbor might never get any indication via TCP
that the other end of the connection is not really there.
One can quicker detect that a PORT connection is not working by
regularly sending PORT messages. PORT in itself does not require any
periodic signaling. PORT Join/Prune messages are only sent when
there is a state change. If the state changes are not frequent
enough, a PORT Keep-Alive message can be sent instead. E.g. if an
implementation wants to send a PORT message, to check that the
connection is working, at least every 60 seconds, then whenever there
is 60 seconds since the the previous message, a Keep-Alive message
could be sent. If there were less than 60 seconds between each Join/
Prune, no Keep-Alive messages would be needed. Implementations
SHOULD support the use of PORT Keep-Alive messages. We RECOMMEND
this to be optional, allowing network administrators to use it as
needed. Note that Keep-Alives can be used by a peer, independently
of whether the other peer supports it.
As described in the previous paragraph, an implementation can make
use of Keep-Alives to regularly send messages and detect when a
connection is not working. For TCP the connection will be reset if
no TCP ACKs are received. A quicker and more reliable way of
detecting that a connection is not working, is to send regular PORT
messages, and have our peer take down the connection if it doesn't
receive them. This can be done by sending Keep-alive messages with a
non-zero holdtime value. If the last received Keep-alive message had
a non-zero holdtime, one tears down the connection if the time
measured in seconds since the last processed PORT message exceeds the
specified holdtime.
Implementations SHOULD support Keep-Alive messages. An
implementation that supports Keep-Alive messages acts as follows when
processing a received PORT message. When processing a Keep-Alive
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message with a non-zero Holdtime value, it MUST set a timer to the
value. We call this timer Connection Expiry Timer (CET). If the CET
is already running, it MUST be reset to the new value. When
processing a Keep-Alive message with a zero Holdtime value, the CET
MUST be stopped if running. When processing a PORT message other
than Keep-Alive, the CET MUST be reset to the last received Holdtime
value if running. If the CET is not running, no action is taken. If
the CET expires, the connection SHOULD be shut down.
It is possible that a router receives Join/Prune 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 ensure it gets a full update for
that interface when it comes back up. This can be done by changing
the GenID, or by terminating and reestablishing the connection.
If a PORT neighbor changes its GenID and a connection is established
or attempting to be established, the local side should generally tear
down the connection and do as described in Section 4.3. However, if
the connection is shared by multiple interfaces and the GenID changes
only for one of them, then there was not a full restart, and one may
simply send a full update similar to other cases when a GenID changes
for an upstream neighbor.
4.3. Actions When a Connection Goes Down
A connection may go down for a variety of reasons. It may be due to
an error condition, or a configuration change. A 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. This may happen
when a new connection ID is configured, PORT is disabled, or a PIM
neighbor expires.
If a PIM neighbor expires, one should free connection state and
downstream oif-list state for the neighbor. A downstream router,
when an upstream neighboring router has expired, will simply update
the RPF for the corresponding state to a new neighbor where it would
trigger Join/Prune 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.
When a connection is no longer available between two PORT enabled PIM
neighbors, they MUST immediately, or on-demand, try to reestablish
the connection following the normal rules for connestion
establishment. The neighbors MUST also start expiry timers so that
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all oif-list state for the neighbor using the connection, gets
expired after JP_HOLDTIME, unless it later gets refreshed by
receiving new Join/Prunes.
The value of JP_HOLDTIME is 215 seconds. This value is based on
section 4.11 of [RFC4601] which says that J/P_HoldTime should be 3.5
* t_periodic where the default for t_periodic is 60 seconds.
4.4. 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, or a previously
PORT enabled neighbor no longer announces any of the PORT Hello
options, one follows the rules in Section 4.3 for taking down
connections and starting timers. Next, one should trigger a full
state update similar to what would be done if the GenID changed in
Datagram Mode. This means sending joins for any state where we
switched from PORT to Datagram Mode for the upstream neighbor.
4.5. 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 a full mesh of connections on a network interface. The
disadvantage is additional delay and queueing when a Join/Prune
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 Join/Prune message 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.
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 Join/Prune
message and there is no currently established connection.
Therefore, this specification recommends but does not mandate the use
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of on-demand Transport connection establishment.
4.6. 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.
4.7. Avoiding a Pair of TCP Connections between Neighbors
To ensure that there is only one TCP connection between a pair of PIM
neighbors, the following set of rules must be followed. Note that
this section applies only to TCP, for SCTP this is not an issue. 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
Join/Prune messages 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
Join/Prune messages to A. (This is independent of which node
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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. PORT Message Definition
It may be desirable for scaling purposes to allow Join/Prune messages
from different PIM protocol families to be sent over the same
Transport connection. Also, it may be desirable to have a set of
Join/Prune 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 PORT message message format.
This will provide both record boundary and demux points when sending
over a stream protocol like TCP/SCTP.
A PORT message may contain PORT options, see Section 5.3. We will
define two PORT options for carrying PIM Join/Prune messages. One
for IPv4 and one for IPv6. For each PIM Join/Prune message to be
sent over the Transport connection, we send a PORT Join/Prune message
containing exactly one such option.
Each PORT message will have the below Type/Length/Value format.
Multiple different TLV types can be sent over the same Transport
connection.
To make sure PIM Join/Prune messages are delivered as soon as the TCP
transport layer receives the Join/Prune buffer, the TCP Push flag
will be set in all outgoing Join/Prune messages sent over a TCP
transport connection.
PORT 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.
PORT 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 Join/Prune message, it is skipped, and
we proceed processing any following PORT messages.
The TLV type field is 16 bits. The range 61440 - 65535 is for
experimental use [RFC3692].
This document defines two message types.
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5.1. PORT Join/Prune Message
PORT Join/Prune 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 | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Exp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface |
| ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PORT Option Type | Option Value Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ . \
/ . /
\ . \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PORT Option Type | Option Value Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The PORT Join/Prune Message is used for sending a PIM Join/Prune.
Message Length: Length in bytes for the value part of the Type/
Length/Value encoding. If no PORT Options were included, the
length would be 12. If n PORT Options with Option Value lengths
L1, L2, ..., Ln are included, the message length will be 12 + 4*n
+ L1 + L2 + ... + Ln.
Reserved: Set to zero on transmission and ignored on receipt.
Exp: For experimental use [RFC3692].
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Interface ID: This is the Interface ID of the Interface ID Hello
option contained in the PIM Hello messages the PIM router is
sending to the PIM neighbor. It indicates to the PIM neighbor
what interface to associate the Join/Prune with.
PORT Options: The message MUST contain exactly one PIM Join/Prune
Port Option, either one PIM IPv4 Join/Prune or one PIM IPv6 Join/
Prune. It MUST NOT contain both. It MAY contain additional
options not defined in this document. A router receiving a PORT
Join/Prune message containing unknown options MUST ignore the
entire PORT message. See Section 5.3 for option definitions.
As can be seen from the packet format diagram, multiple Join/Prune
messages can go into one TCP/SCTP stream from the same or different
Interface IDs.
5.2. PORT Keep-alive Message
PORT Keep-alive 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 | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Exp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Holdtime | PORT Option Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Value Length | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . +
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ . \
/ . /
\ . \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PORT Option Type | Option Value Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The PORT Keep-alive Message is used to regularly send PORT messages
to verify that a connection is alive. They are used when other PORT
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messages are not sent of the desired frequency.
Message Length: Length in bytes for the value part of the Type/
Length/Value encoding. If no PORT Options were included, the
length would be 6. If n PORT Options with Option Value lengths
L1, L2, ..., Ln are included, the message length will be 6 + 4*n +
L1 + L2 + ... + Ln.
Reserved: Set to zero on transmission and ignored on receipt.
Exp: For experimental use [RFC3692].
Holdtime: This specifies a holdtime in seconds for the connection.
A non-zero value means that the connection SHOULD be gracefully
shut down if no further PORT messages are received within the
specified time. This is measured on the receiving side by
measuring the time from one PORT message has been processed until
the next has been processed. Note that this is done for any PORT
message, not just keep-alive messages. A hold time of 0 disables
the keep-alive mechanism.
PORT Options: A keep-alive message MUST NOT contain any of the
options defined in this document. It MAY contain other options
not defined in this document. See Section 5.3 for option
definitions.
5.3. PORT Options
Each PORT Option is a TLV. The type is 16 bits. PORT Option types
are assigned by IANA, except the range 61440 - 65535 which is for
experimental use [RFC3692]. The length specifies the length of the
value in bytes. Below are the two options defined in this document.
PIM IPv4 Join/Prune Option
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PIM IPv4 Join/Prune Option Format
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PORT Option Type = 1 | Option Value Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PIMv2 Join/Prune Message |
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The IPv4 Join/Prune Option is used to carry a PIMv2 Join/Prune
message that has all IPv4 encoded addresses in the PIM payload.
Option Value Length: The number of bytes that make up the PIMv2
Join/Prune message.
PIMv2 Join/Prune Message: PIMv2 Join/Prune message and payload with
no IP header in front of it.
PIM IPv6 Join/Prune Option
PIM IPv6 Join/Prune Option Format
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PORT Option Type = 2 | Option Value Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PIMv2 Join/Prune Message |
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The IPv6 Join/Prune Option is used to carry a PIMv2 Join/Prune
message that has all IPv6 encoded addresses in the PIM payload.
Option Value Length: The number of bytes that make up the PIMv2
Join/Prune message.
PIMv2 Join/Prune Message: PIMv2 Join/Prune message and payload with
no IP header in front of it.
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6. Explicit Tracking
When explicit tracking is used, a router keeps track of join state
for individual downstream neighbors on a given interface. This is
done for all PORT joins and prunes. It may also be done for native
join/prune messages, if all neighbors on the LAN have set the T bit
of the LAN Prune Delay option. In the discussion below we will talk
about ET (explicit tracking) neighbors, and non-ET neighbors. The
set of ET neighbors always includes the PORT neighbors. The set of
non-ET neighbors consists of all the non-PORT neighbors unless all
neighbors have set the LAN Prune Delay T bit. Then the ET neighbors
set contains all neighbors.
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) state, the router starts forwarding traffic on an
interface when a Join is received from a neighbor on such an
interface. When a non-ET neighbor sends a Prune, as specified
[RFC4601], if no Join is sent to override this Prune before the
expiration of the Override Timer, the upstream router concludes that
no non-ET neighbor is interested. If no ET neighbors are interested,
the interface can be removed from the oif-list. When an ET neighbor
sends a Prune, one removes the join state for that neighbor. If no
other ET or non-ET neighbors are interested, the interface can be
removed from the oif-list. When a PORT neighbor sends a prune, there
can be no Prune Override, since the Prune is not visible to other
neighbors.
For (S,G,rpt) state, the router needs to track Prune state on the
shared tree. It needs to know which ET neighbors have sent prunes,
and whether any non-ET neighbors have sent prunes. 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,rpt)-prune. With
ET one needs to do this check per ET neighbor. That is, the packet
should be forwarded unless all ET neighbors that have sent
(*,G)-joins have also sent (S,G,rpt)-prunes, and if a non-ET neighbor
has sent a (*,G)-join, whether there also is non-ET (S,G,rpt)-prune
state.
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7. Multiple Address-Family Support
To allow for efficient use of router resources, one can mux Join/
Prune messages of different address families on the same Transport
connections. There are two ways this can be accomplished, one using
a common message format over a TCP connection and the other using
multiple streams over a single SCTP connection.
Using the common message format described previously in this
specification, using different PORT options, both IPv4 and IPv6 based
Join/Prune messages can be encoded within the same Transport
connection.
When using SCTP multi-streaming, the common message format is still
used to convey address family information but an SCTP association is
used, on a per-family basis, to send data concurrently for multiple
families. 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
TCP connections can be authenticated using TCP-AO [RFC5925]. When
using SCTP, [RFC4895] can be used for authentication on a per SCTP
association basis. Also GTSM [RFC5082] can be used to help prevent
spoofing.
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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.
10.1. PORT Message Type Registry
A registry for PORT message types is requested. The message type is
a 16-bit integer, with values from 0 to 65535. An RFC is required
for assignments in the range 0 - 61439. This document defines one
PORT message type. Type 1, PORT Join/Prune Message. The type range
61440 - 65535 is for experimental use [RFC3692].
The initial content of the registry should be as follows:
Type Name Reference
------------- ------------------------------- ---------------
0 Reserved this document
1 Join/Prune this document
2 Keep-alive Message this document
3-61439 Unassigned
61440-65535 Experimental this document
10.2. PORT Option Type Registry
A registry for PORT option types is requested. The option type is a
16-bit integer, with values from 0 to 65535. An RFC is required for
assignments in the range 0 - 61439. This document defines two PORT
option types. Type 1, PIM IPv4 Join/Prune Message; and Type 2, PIM
IPv6 Join/Prune Message. The type range 61440 - 65535 is for
experimental use [RFC3692].
The initial content of the registry should be as follows:
Type Name Reference
------------- ------------------------------- ---------------
0 Reserved this document
1 PIM IPv4 Join/Prune Message this document
2 PIM IPv6 Join/Prune Message this document
3-61439 Unassigned
61440-65535 Experimental this document
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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, Sameer
Gulrajani, Thomas Morin, Dimitri Papadimitriou, Bharat Joshi, Rishabh
Parekh, Manav Bhatia and Pekka Savola.
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
[I-D.gulrajani-pim-hello-intid]
Gulrajani, S. and S. Venaas, "An Interface ID Hello Option
for PIM", draft-gulrajani-pim-hello-intid-00 (work in
progress), February 2011.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-
PIM)", RFC 5015, October 2007.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, October 2007.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, June 2010.
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.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
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Considered Useful", BCP 82, RFC 3692, January 2004.
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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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