Network Working Group Eric C. Rosen (Editor)
Internet Draft Arjen Boers
Intended Status: Proposed Standard Yiqun Cai
Expires: April 28, 2009 IJsbrand Wijnands
Cisco Systems, Inc.
October 28, 2008
MVPN: Optimized use of PIM, Wild Card Selectors,
Bidirectional Tunnels, Extranets
draft-rosen-l3vpn-mvpn-mspmsi-01.txt
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Abstract
Specifications for a number of important topics were arbitrarily
omitted from the initial MVPN specifications, so that those
specifications could be "frozen" and advanced. The current document
provides some of the missing specifications. The topics covered are:
(a) using Wild Card selectors to bind multicast data streams to
tunnels, (b) using Multipoint-to-Multipoint Label Switched Paths as
tunnels, (c) binding bidirectional customer multicast data streams to
specific tunnels, (d) running PIM (i.e., sending and receiving
multicast control traffic) over a set of tunnels that are created
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only if needed to carry multicast data traffic, and (e) extranets.
Table of Contents
1 Specification of requirements ......................... 3
2 Introduction .......................................... 3
2.1 Topics Covered ........................................ 3
2.2 Terminology ........................................... 4
3 Wild Card Selectors in S-PMSI A-D Routes .............. 5
4 Binding C-(*,G) to a Unidirectional P-Tunnel .......... 6
5 S-PMSI Procedures for Using MP2MP LSPs as P-tunnels ... 6
5.1 General Procedures: MS-PMSIs .......................... 7
5.2 Use of Multiple MP2MP LSPs ............................ 8
5.2.1 Binding C-(S,G) ....................................... 8
5.2.2 Binding C-(*,G) Flows from Unidirectional C-trees ..... 9
5.2.3 Binding C-(*,G) Flows from Bidirectional C-trees ...... 9
5.2.4 Binding C-(*,*) ....................................... 10
5.2.5 Default Tunnel Identifier ............................. 11
5.3 Single MP2MP LSP ...................................... 12
6 PIM over MS-PMSI ...................................... 13
7 S-PMSI Join Extensions ................................ 14
7.1 mLDP P2MP P-Tunnels ................................... 14
7.2 IPv6 (S,G) with GRE P-tunnels ......................... 15
7.3 Multiple S-PMSI Joins per Datagram .................... 15
8 Extranets using PIM as the MVPN Control Plane ......... 16
8.1 Default PMSI .......................................... 16
8.2 Red method ............................................ 17
8.2.1 Control Plane RPF Check ............................... 17
8.2.2 Data Plane RPF Check .................................. 17
8.3 Blue method ........................................... 18
8.4 Binding Specific Extranet C-Flows to S-PMSIs .......... 18
9 IANA Considerations ................................... 19
10 Security Considerations ............................... 19
11 Authors' Addresses .................................... 20
12 Normative References .................................. 20
13 Informative References ................................ 21
14 Full Copyright Statement .............................. 21
15 Intellectual Property ................................. 21
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1. Specification of requirements
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].
2. Introduction
The documents [MVPN] and [MVPN-BGP] contain specifications for a
large number of MVPN topics. However, a number of important topics
have been declared to be "out of scope" of those documents. This
document provides the specifications for some of those topics. This
document is not expected to be read as a stand-alone document;
terminology from [MVPN] is used freely and knowledge of [MVPN] and
[MVPN-BGP] is presupposed.
Any necessary procedures not explicitly specified here are as in
[MVPN] and/or [MVPN-BGP].
2.1. Topics Covered
The topics covered in this document are the following:
- The use of Wild Card Selectors in S-PMSI A-D routes.
In [MVPN] and [MVPN-BGP], one can use an S-PMSI A-D route to
assign a particular C-multicast flow, identified as C-(S,G), to a
particular S-PMSI. The Wild Card Selectors specified in this
document provide additional functionality:
* One can send an S-PMSI A-D route whose semantics are "assign
all the traffic traveling the C-(*,G) tree to this S-PMSI".
* One can send an S-PMSI A-D route whose semantics are "use
this S-PMSI as the default method for carrying any C-(S,G)
traffic that isn't assigned to a different S-PMSI". That is,
it allows for the use of S-PMSIs as the default PMSIs for
carrying data traffic.
- The use of Multipoint-to-Multipoint Label Switched Paths (MP2MP
LSPs) as P-tunnels.
A new kind of PMSI is defined, the MS-PMSI. An S-PMSI is defined
in [MVPN] to have a single PE as its transmitter. An MS-PMSI is
a set of S-PMSIs which together are instantiated by a single
MP2MP LSP. This allows one to create P-tunnels which contain
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only a subset of the PEs attached to a given VPN, but which can
be used by any member of that subset to transmit to the other
members of the subset. MS-PMSIs are advertised using the S-PMSI
A-D routes of [MVPN] and [MVPN-BGP].
- PIM over MS-PMSI.
[MVPN] specifies how to run PIM [PIM] as the multicast routing
protocol of a particular MVPN, by running it over an MI-PMSI for
that MVPN. In this specification, we show how to run PIM over an
MS-PMSI. A potential disadvantage of running PIM over MI-PMSI is
that it can result in the creation of P-tunnels that only carry
PIM messages, but do not carry multicast data. However, when PIM
is run over an MS-PMSI, there is never any need to create a P-
tunnel just for control messages; the only P-tunnels needed are
those which carry multicast data.
- MVPN Extranets with PIM Control Plane.
In an MVPN "extranet", the transmitter of a multicast traffic
flow is in a different VPN than the receivers. Additional
procedures are defined to determine how the traffic is associated
with a particular MI-PMSI or MS-PMSI, and how the RPF checks are
done.
2.2. Terminology
In the following, we will sometimes talk of a PE receiving traffic
from a PMSI and then discarding it. If PIM is being used as the
multicast control protocol between PEs, this always implies that the
discarded traffic will not be seen by PIM on the receiving PE.
In the following, we will sometimes speak of an S-PMSI A-D route
being "ignored". When we say the route is "ignored", we do not mean
that it's normal BGP processing is not done, but that the route is
not considered when determining which P-tunnel to use when sending
multicast data, and that the MPLS label values it conveys are not
used. We will generally use "ignore" in quotes to indicate this
meaning.
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3. Wild Card Selectors in S-PMSI A-D Routes
As specified in [MVPN-BGP], an S-PMSI A-D route can be used to bind a
specified C-multicast flow to a specified P-tunnel. The P-tunnel is
identified in the PMSI Tunnel Attribute (PTA) of the A-D route. The
C-multicast flow is identified as (C-S,C-G), and specified as part of
the route's NLRI. The NLRI is defined as follows:
+-----------------------------------+
| RD (8 octets) |
+-----------------------------------+
| Multicast Source Length (1 octet) |
+-----------------------------------+
| Multicast Source (Variable) |
+-----------------------------------+
| Multicast Group Length (1 octet) |
+-----------------------------------+
| Multicast Group (Variable) |
+-----------------------------------+
| Originating Router's IP Addr |
+-----------------------------------+
The Multicast Source field contains the C-S address, and the Multi-
cast Group field contains the C-G address.
However, [MVPN-BGP] does not specify any means of encoding wild cards
("*", in multicast terminology) in the Source or Group fields.
This omission makes it difficult to provide optimized multicast rout-
ing for customers that use ASM ("Any Source Multicast") multicasts,
in which flows may be traveling along "shared" C-trees. By "shared
C-trees", we mean both the unidirectional "RPT trees" used in sparse
mode, and the bidirectional trees used in BIDIR-PIM [BIDIR-PIM].
When a customer is using ASM multicast, it is useful to be able to
select the set of flows that are traveling along a shared C-tree, and
to bind that entire set of flows to a specified P-tunnel. Conceptu-
ally, we would like to have a way to express that we want (C-*,C-G)
traffic bound to the specified P-tunnel.
Another useful feature would be a way of using an S-PMSI A-D route to
say "by default, all multicast traffic (within a given VPN) that has
not been bound to any other P-tunnel is bound to the specified P-tun-
nel". To do this we, need to have a way to express that we want
(C-*, C-*) traffic bound to the P-tunnel.
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This specification therefore establishes the following convention.
The use of a zero length source or group field is to be interpreted
as specifying a wild card value for the respective field. The fol-
lowing two combinations MUST BE supported:
- C-(*,G): Source Wildcard, Group specified.
- C-(*,*): Source Wildcard, Group Wildcard.
This specification does not provide support for the combination of a
specified source and a group wildcard. A received S-PMSI A-D route
specifying this combination will be "ignored".
4. Binding C-(*,G) to a Unidirectional P-Tunnel
Consider an S-PMSI A-D Route whose NLRI specifies C-(*,G), and which
contains a PTA that specifies a unidirectional P-tunnel. The P-
tunnel may be a P2MP LSP, or it may be a unidirectional PIM-created
multicast distribution tree specified either as P-(*,G) or as
P-(S,G).
If C-G is known to be an SSM group address, the S-PMSI A-D route is
"ignored".
Otherwise, the semantics of this S-PMSI A-D route are the following:
the originator of the S-PMSI A-D route is saying that if it receives,
over a VRF interface, any traffic that is traveling on the C-(*,G)
shared tree, it will transmit such traffic on the specified P-tunnel.
Any PE interested in receiving such traffic from the originator MUST
join that P-tunnel.
(A PE receiving C-(S,G) multicast traffic can always tell whether
that traffic is traveling on a C-(*,G) shared tree by consulting its
C-PIM state. Similarly, each PE in an MVPN, by virtue of running C-
PIM, knows whether it is interested in receiving traffic from the
C-(*,G) tree.)
5. S-PMSI Procedures for Using MP2MP LSPs as P-tunnels
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5.1. General Procedures: MS-PMSIs
There are two methods for using MP2MP LSPs as P-tunnels. In one
method, a single MP2MP LSP is used to connect n PE routers. In
another method, multiple MP2MP LSPs are used. These two methods are
considered separately. Which method is in use is a matter of
provisioning.
In both cases, an S-PMSI A-D route whose PTA specifies a particular
MP2MP LSP MUST be originated by the PE that is the root of the LSP.
The Tunnel Identifier for the MP2MP LSP consists of an MLDP MP2MP FEC
element [MLDP], which itself consists of an IP address of the
originating PE router, followed by an "opaque value" identifying the
MP2MP LSP in the context of that PE router. This opaque value may be
configured or autogenerated, and there is no need for different PEs
attached to a given MVPN to use the same opaque value. The IP
address which appears in the tunnel identifier field of the PTA MUST
be the same IP address that the PE uses for sending and receiving PIM
control messages.
According to the definition of S-PMSI in [MVPN], only a single PE can
transmit onto a given S-PMSI. However, an MP2MP LSP that contains n
PEs can therefore be used to instantiate n S-PMSIs, each of which has
a different PE as its transmitter. Each PE can use the tunnel to
transmit data to the other n-1 PEs. Therefore when a MP2MP LSP is
specified in the PTA of an S-PMSI A-D route, we consider that it
implicitly advertises a number of S-PMSIs: one for the root PE, and
one for each PE that receives and processes the route. We will call
the latter S-PMSIs the "implicitly advertised reverse S-PMSIs" (or
just "reverse S-PMSIs").
When an MP2MP LSP is specified in the PTA of an S-PMSI A-D route, we
will use the term "MS-PMSI" to refer the set of S-PMSIs that
(including the reverse S-PMSIs) that are advertised (explicitly or
implicitly) in that A-D route. The PE that originated the S-PMSI A-D
route is known as the "root" of the MS-PMSI. When PE1 is the root of
an MS-PMSI, we will sometimes refer to the MS-PMSI as "PE1's MS-
PMSI". (Of course, a given PE may be the root for more than one MS-
PMSI, for the same or different MVPNs. Rules governing the
association of an S-PMSI A-D route with a given MVPN are as specified
in [MVPN] and [MVPN-BGP].)
If the PTA in the S-PMSI A-D route contains an MPLS label, then any
PE that, as a result of having received that route, transmits a
packet onto the MS-PMSI will first push that label onto the packet's
label stack. The interpretation of that label when the packet is
received is as specified in [MVPN] and [MVPN-BGP]. The use of this
label allows multiple VPNs to share a single MP2MP LSP.
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An S-PMSI A-D route whose PTA specifies a MP2MP LSP MUST be "ignored"
UNLESS it is originated by the root of the LSP. Any MPLS label
specified in the PTA of an "ignored" route MUST be ignored. Any PE
Distinguisher Labels specified in the "ignored" route MUST be
ignored.
5.2. Use of Multiple MP2MP LSPs
In this method, each PE attached to a given MVPN is potentially the
root of a distinct MP2MP LSP. Each such PE may originate an S-PMSI
A-D route whose PTA specifies an MP2MP LSP for which the originating
PE is the root. In effect, each such PE advertises an MS-PMSI. We
will sometimes refer to the MS-PMSIs as "partitions", and to the PE
that advertised it as the root of the MS-PMSI or the root of the
partition. This notion is useful both in support for BIDIR-PIM C-
multicast traffic and for running PIM over MS-PMSI. Details are
given in later sections.
The procedures that follow presuppose when a packet is received from
a MP2MP LSP, it can be associated with one or more VRFs, and
processed in the context of that VRF or VRFs. If the PTA that
specified the MP2MP LSP has no MPLS label, then all packets received
from the LSP are associated with the same set of VRFs. If the PTA
did specify a label, then received packets must will carry a label
(beneath the label that identifies the LSP itself), and the label
must be processed in order to determine the context.
5.2.1. Binding C-(S,G)
When PE1 advertises an S-PMSI A-D route that binds a C-(S,G) flow to
a MP2MP LSP, the semantics are as follows. PE1 is stating that any
C-(S,G) traffic that it needs to transmit to other PEs will be
transmitted on the specified LSP. Any other PE that needs to receive
such traffic from PE1 (i.e., any other PE that needs to receive
C-(S,G) traffic and which has selected PE1 as the upstream PE for C-
S) MUST join that LSP.
If a PE has joined the LSP, but does not need to receive the C-(S,G)
traffic, or if it needs to receive C-(S,G) traffic but has not
selected PE1 as the upstream PE for C-S, then the PE MUST discard any
such received traffic. Please note that if PIM is being used as the
multicast control protocol, traffic that is discarded will not be
seen by PIM.
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5.2.2. Binding C-(*,G) Flows from Unidirectional C-trees
When PE1 advertises an S-PMSI A-D route that binds C-(*,G) to a MP2MP
LSP, where C-G is not an SSM group, and the C-(*,G) traffic is
traveling on a unidirectional shared C-tree, the semantics are as
follows. PE1 is stating that any traffic to C-G that is traveling
the shared C-tree and which PE1 needs to transmit to other PEs will
be transmitted on the specified LSP. Any other PE that needs to
receive such traffic from PE1 (i.e., any other PE that needs to
receive C-(*,G) traffic and which has selected PE1 as the upstream PE
for the C-RP corresponding to the C-G group) MUST join that LSP.
If a PE has joined the LSP, but does not need to receive the C-(*,G)
traffic, or if it needs to receive C-(*,G) traffic but has not
selected PE1 as the upstream PE for the C-RP that corresponds to C-G,
then the PE MUST discard any such received traffic. Please note that
if PIM is being used as the multicast control protocol, traffic that
is discarded will not be seen by PIM.
5.2.3. Binding C-(*,G) Flows from Bidirectional C-trees
When PE1 advertises an S-PMSI A-D route that binds C-(*,G) to a MP2MP
LSP, where C-G is not an SSM group, and the C-(*,G) traffic is
traveling on a bidirectional shared C-tree, the semantics are as
follows:
- PE1 is stating that any traffic to C-G that it (PE1) needs to
send downstream will be sent on the specified LSP (or
equivalently, on the MS-PMSI that it instantiates by virtue of
the A-D route having been sent).
- Any other PE that is interested in receiving C-(*,G) traffic MUST
join the specified LSP (or equivalently, must become a member of
the MS-PMSI).
- Any other PE, say PE2, that (a) has traffic to C-G to send
upstream and (b) has selected PE1 as its upstream PE for the C-
RPA corresponding to C-G, MUST join the specified LSP (become a
member of the MS-PMSI), and MUST send such traffic on the
specified LSP. (I.e., such traffic is bound to the MS-PMSI
instantiated by the MP2MP LSP that is rooted at PE2.)
- If a PE, say PE3, has joined the specified LSP, but does not need
to receive the C-(*,G) traffic, or has not selected PE1 as the
upstream PE for the C-RPA corresponding to C-G, then PE3 MUST NOT
send any C-(*,G) traffic on that LSP, and MUST discard any
C-(*,G) traffic it received on that LSP.
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These procedures implement, for S-PMSIs, the "partitioning" scheme
described in section 11.2 of [MVPN], with each MS-PMSI being a
"partition".
The specification given so far requires an S-PMSI A-D route to be
sent for each C-(*,G) that is using a bidirectional C-tree. A more
efficient method is given in the next section.
5.2.4. Binding C-(*,*)
When PE1 advertises an S-PMSI A-D route that binds C-(*,*) to a
specified MP2MP LSP of which PE1 is the root, the semantics are as
that the MP2MP LSP is to be used to carry C-multicast traffic in the
following sets of cases:
1. If PE1 has C-(S,G) traffic that is traveling on a source-
specific C-tree, and PE1 needs to transmit that data to one or
more other PEs, and PE1 has not bound C-(S,G) or C-(*,G) to a
different P-tunnel, then the C-(S,G) traffic is sent by PE1 on
the specified MP2MP LSP.
2. If PE1 has C-(*,G) traffic that is traveling on a
unidirectional shared C-tree, and PE1 needs to transmit that
data to one or more other PEs, and PE1 has not bound C-(*,G) to
a different P-tunnel, then the C-(*,G) traffic is sent by PE1
on the specified MP2MP LSP.
3. If PE1 has C-(*,G) traffic that is traveling on a bidirectional
shared C-tree, and PE1 needs to transmit that data to one or
more other PEs, and PE1 has not bound C-(*,G) to a different P-
tunnel, then the C-(*,G) traffic is sent by PE1 on the
specified MP2MP LSP.
4. Consider some other PE, PE2, that has received the S-PMSI A-D
route from PE1. If PE2 has C-(*,G) traffic that is traveling
on a bidirectional shared C-tree, and PE2 needs to transmit
that traffic UPSTREAM, and PE2 has selected PE1 as the upstream
PE for the C-RPA corresponding to C-G, and PE1 has not bound
C-(*,G) to any other P-tunnel, then the C-(*,G) traffic is sent
by by PE2 on the specified MP2MP LSP.
5. If a PE receives traffic from a particular MS-PMSI, and the
traffic is traveling a unidirectional C-(*,G) or C-(S,G) tree,
and the root of the MS-PMSI is not the PE's selected upstream
PE for the C-(*,G) or C-(S,G), the PE MUST discard the traffic.
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6. If a PE receives traffic from a particular MS-PMSI, and the
traffic is traveling a bidirectional C-(*,G) tree, and the PE's
selected upstream PE for the C-RPA corresponding to C-G is not
the root of the MS-PMSI, then the PE MUST discard the traffic.
With respect to traffic traveling a bidirectional C-tree, these
procedures implement, for S-PMSIs, the "partitioning" scheme
described in section 11.2 of [MVPN], without the need to send an S-
PMSI A-D route for each C-(*,G) that is using a bidirectional C-tree.
Each PE becomes the root of an MS-PMSI, and binds the double wildcard
selector to it. The MS-PMSIs serve as the "partitions". The MS-PMSI
rooted at PE1 becomes the default MS-PMSI for all traffic that PE1
needs to send downstream to other PEs. It also becomes the default
MS-PMSI for all traffic that others PEs need to send upstream, as
long as those other PEs have selected PE1 as the upstream PE for the
C-RPA corresponding to that traffic.
Note that other PEs SHOULD NOT join the specified MP2MP LSP unless
they have a need to send or receive data over it. A PE knows when it
needs to receive data by virtue of having certain multicast state in
its C-PIM instance. With regard to multicast data traveling on a
bidirectional C-(*,G) tree, a PE may not know whether it has to send
data until such data actually arrives over a VRF interface; the PE
may be on a "sender-only" branch. However, the PE in this case would
have to know, through provisioning or some automatic procedure such
as "Bootstrap Routing Protocol for PIM" (BSR) [BSR], the set of C-
RPAs that are being used to support C-(*,G) traffic. For each C-RPA,
the PE could join the MP2MP LSP advertised by its selected upstream
PE for that C-RPA. Alternatively the PE could defer joining the LSP
until it actually has data to send.
5.2.5. Default Tunnel Identifier
To identify a MP2MP LSP, the PMSI Tunnel Attribute of an S-PMSI A-D
route contains an MP2MP FEC Element [mLDP] in its "Tunnel Identifier"
field. This contains the IP address of the PE at the root of the
LSP, as well as an "opaque value" which is unique at that PE. Each
PMSI Tunnel is associated at its root PE with a particular VRF, and
each VRF in a given PE has a unique default RD. Therefore one way to
uniquely identify a MP2MP LSP is to use a MP2MP FEC Element whose
Opaque Value length is 8 and whose Opaque Value value is the default
RD of the associated VRF. This method of assigning a Tunnel
Identifier MUST be the default method for any PMSI Tunnel which is
bound to C-(*,*) traffic. Other methods MAY be available as well.
Note that if aggregation of multiple VPNs onto a single default MS-
PMSI is not being supported, this method of assigning the Tunnel
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Identifier allows each PE to algorithmically determine the Tunnel
Identifier that has been assigned by a particular upstream PE. A PE
decides to join a particular MS-PMSI because it has chosen that MS-
PMSI's root as the upstream PE for a particular VPN-IP address. The
RD of that VPN-IP address is the contents of the Opaque Value field
of the corresponding MS-PMSI.
5.3. Single MP2MP LSP
When a single MP2MP LSP is used for a given VPN (rather than multiple
MP2MP LSPs), the PE at the root of the LSP MUST advertise it in the
PTA of an S-PMSI A-D root. The PE that is at the root of the LSP
MUST include a "PE Distinguisher Labels" attribute in either in its
I-PMSI A-D route, or in the S-PMSI A-D route containing the PTA that
identifies the LSP. The PE MUST use the attribute to bind an
upstream-assigned MPLS label to the IP address of each other PE that
attaches to the same MVPN (as determined by the RTs of the A-D
route). That is, the PE as the root of the LSP assigns a distinct
label to each of the other PEs attaching to the same MVPN. This set
of PEs is learned via the reception of I-PMSI A-D routes.
The procedures for using the single MP2MP LSP differ from the
procedures for using a mesh of MP2MP LSPs only in the following way.
Let PE1 be the root of the LSP. When a packet that is traveling on a
unidirectional C-tree is transmitted on the LSP by a particular PE,
say PE2, PE2 must push on the packet's label stack the label that PE1
assigned to PE2 via the procedure above. When a packet that is
traveling on a bidirectional C-tree is transmitted on the LSP by PE2,
it must push on the packet's label stack the label that PE1 assigned
to PE3, where PE3 is the upstream PE that PE2 has selected for the C-
RPA corresponding to C-G.
For unidirectional flows, this allows the transmitter to be
identified, and for bidirectional flows, this allows the partition to
be identified. Packets received from the wrong upstream PE or from
the wrong partition MUST be discarded. (In effect, this is a case of
LSP hierarchy, where the PE Distinguisher Labels represent the set of
MP2MP LSPs described in previous sections, but those LSPs are all
tunneled through a single MP2MP LSP.)
If the PTA identifying the MP2MP LSP contains an MPLS label, then
that label shall appear in the label stack immediately preceding the
label specified in the PE Distinguisher Labels attribute.
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6. PIM over MS-PMSI
[MVPN] provides two alternative means of distributing C-multicast
routing information: PIM or BGP. Procedures for running PIM over
MI-PMSI are specified in that document. However, a number of
efficiencies can be obtained by running PIM instead over an MS-PMSI,
instantiated as a set of MP2MP LSPs. The procedures for this are as
follows.
Each PE that attaches to a given MVPN MUST originate an Intra-AS I-
PMSI A-D route that does NOT contain a PTA. Each such PE MUST also
originate an S-PMSI A-D route whose PTA is a MP2MP LSP rooted at the
originating PE. This S-PMSI A-D MUST bind the LSP to the "double
wildcard" (*,*). The use of these LSPs for sending and receiving
data traffic is as specified in the previous section. In effect,
each PE in the MVPN has advertised an MS-PMSI for which it is the
root.
If PE1 needs to direct a PIM Join/Prune message to PE2, PE1 MUST join
the PE2's MS-PMSI by joining the LSP advertised in PE2's
corresponding S-PMSI A-D route. The PIM J/P messages MUST be sent
over that MS-PMSI.
If PE1 does not need to direct a PIM Join/Prune message to PE2, then
PE1 SHOULD not join the LSP advertised in PE2's S-PMSI A-D route, as
PE1 will not be receiving any multicast data on that LSP.
Any PIM Hellos that PE1 sends MUST be sent on the LSP advertised in
PE1's S-PMSI A-D route above.
Standard PIM procedures are to be used. Note though that the data
handling procedures of the previous section will prevent PIM from
ever seeing any packets that come from the wrong transmitter or that
are in the wrong partition; when such packets are received they are
discarded, rather than being passed to PIM's state machinery. As a
result, such packets do not cause Asserts to be generated. Other
standard PIM procedures, such as Join Suppression and Prune Override
may come into play, however.
By running PIM over MS-PMSI instead of over MI-PMSI, one completely
avoids the need to have PEs join P-tunnels that would carry only
control messages. A PE need not ever join a particular a P-tunnel
unless it either has data to send on it, or needs to receive data on
it.
It is also possible to run PIM over MS-PMSI when a single MP2MP LSP
is used. In that case, the PE at the root of the LSP MUST include a
PE Distinguisher Labels attribute in its S-PMSI A-D route, and must
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assign a label to each of the other PEs that attach to the same MVPN.
(This set is auto-discovered through the I-PMSI A-D routes.) When
sending a PIM J/P packet, one must push onto its label stack the
label identifying the PE to which the J/P packet is being directed.
When receiving a PIM J/P packet, a PE discards any that are not
carrying the PE distinguisher label that has been bound to its own IP
address.
All other MVPN-specific PIM procedures are as specified in [MVPN].
7. S-PMSI Join Extensions
7.1. mLDP P2MP P-Tunnels
The S-PMSI Join message is defined in section 7.4.2.2 of [MVPN]. In
this specification, we define the "type 2" and "type 3" S-PMSI Joins,
which are used when the S-PMSI tunnel is a P2MP LSP created by mLDP,
and the tunnel is to carry C-flows of, respectively, IPv4 or IPv6
multicast traffic.
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 | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-Source
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.......
| C-Group
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.......
| FEC Element
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.......
| Padding
+-+-+-+-+-+-+-+.......
Type (8 bits):
- 2 if C-Source and C-Group are IPv4 addresses,
- 3 if C-Source and C-Group are IPv6 addresses.
Length (16 bits): the total number of octets in the Type, Length,
Reserved and Value fields combined, rounded up to the next multiple
of 4, encoded as an unsigned binary integer.
Reserved (8 bits): This field SHOULD be zero when transmitted, and
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MUST be ignored when received.
C-Source: address of the traffic source in the VPN
- for type 2, a 32-bit IPv4 address
- for type 3, a 128-bit IPv6 address
C-Group: address of the traffic destination in the VPN
- for type 2, a 32-bit IPv4 address
- for type 3, a 128-bit IPv6 address
FEC Element: this variable length field is a P2MP FEC element,
encoded as a TLV as specified in [MLDP].
Padding: 0-3 bytes, as needed for 32-bit alignment. The padding
bytes SHOULD be zero on transmission and MUST be ignored on
reception.
7.2. IPv6 (S,G) with GRE P-tunnels
MVPN defines the S-PMSI Join type used when assigning IPv4 (S,G) to a
GRE P-tunnel. When assigning IPv6 (S,G) to a GRE P-tunnel, S-PMSI
type 4 is used, and the C-Source and C-Group are IPv6 addresses.
7.3. Multiple S-PMSI Joins per Datagram
A single UDP datagram MAY carry multiple S-PMSI Joins, as many as can
fit entirely within it. If there are multiple S-PMSI Joins in a UDP
datagram, they MUST be of the same S-PMSI Join type. The end of the
last S-PMSI Join (as determined by the S-PMSI Join length field) MUST
coincide with the end of the UDP datagram, as determined by the UDP
length field. When processing a received UDP datagram that contains
one or more S-PMSI Joins, a router MUST be able to process all the S-
PMSI Joins that fit into the datagram.
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8. Extranets using PIM as the MVPN Control Plane
Suppose there are two VPNs. VPN1 consists of a set of VRFs, each of
which has been configured with RT1 as it export and import Route
Target. VPN2 consists of a set of VRFs, each of which has been
configured with RT2 as it export and import Route Target. For
convenience, we will use the term "blue" instead of "RT1" and the
term "red" instead of "RT2". Thus we will call VPN1 the "blue VPN"
and VPN2 the "red VPN". Similarly, the blue VPN consists of a number
of "blue sites" containing "blue systems"; these sites are attached
to PEs via VRF interfaces that are associated with "blue VRFs".
We want to create an MVPN extranet in which blue receivers can join
multicast groups whose sources and/or RPs are red.
The first step is to ensure that the blue VRFs (or the subset of blue
VRFs whose attached sites are allowed to receive multicasts from red
sources) import routes to the red sources. This is done as follows:
- The red VRFs are configured so that the subset of red routes that
are to be part of the extranet are exported with a seconds RT
value (call it RT3), as well as with RT2. For convenience, we
will call RT3 "violet".
- The blue VRFs are configured so that they import violet routes as
well as blue routes.
There are two different methods of providing the extranets, which
will shall call the "red method" and the "blue method". (Remember
that the red VPN contains the transmitter, and the blue VPN contains
the receivers.)
This document assumes that in the case of non-SSM extranet multicast
groups, the mapping between a group address and an RP is pre-
configured in the PEs.
This document does not provide support for bidirectional C-trees in
extranets.
8.1. Default PMSI
Some of the procedures subsequently specified in this section are
largely independent of whether PIM is used with (a) an MI-PMSI or (b)
with an MS-PMSI that has been bound to the double wildcard. We will
use the term "default PMSI" as a general term to mean either (a) or
(b), depending upon which technique is actually being used in a given
network.
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8.2. Red method
In the "red method", extranet multicasts are carried by default in
the default PMSI of the red VPN, which we will of course call the
"red PMSI".
To use this method, blue VRFs must be configured to import "red" I-
PMSI A-D routes and red S-PMSI A-D routes. If MI-PMSIs are being
used, the blue VRFs must immediately join the P-tunnels specified in
the red I-PMSI A-D routes. If MS-PMSIs are being used, a blue VRF
need not join the MS-PMSI P-tunnel rooted at a particular PE unless a
PIM Join needs to be sent to that PE.
The PIM C-instance associated with a blue VRF will treat the red and
blue default PMSIs as two different PIM interfaces.
The blue VRFs must also be configured to "associate" violet unicast
routes with the red default PMSI. What this means is that the red
default PMSI will be considered to be the RPF interface for the
violet unicast routes. The RPF interface for the blue unicast routes
remains, as usual, the blue default PMSI.
All that remains to be specified is how the control plane and data
plane RPF checks are done. Apart from these MVPN-specific procedures
for the RPF check, ordinary PIM procedures are used.
8.2.1. Control Plane RPF Check
Suppose a PE receives a PIM Join(S,G) from a CE, over a VRF interface
that is associated with a blue VRF. The PE does the RPF check for S
by looking up S in the blue VRF. If the route matching S is a blue
route (i.e., carries the blue RT but not the violet RT), then a Join
is sent over the blue default PMSI. However, if the route matching S
is a violet route (i.e., carries the violet RT), a Join is sent over
the red default PMSI.
If the PE receives a PIM Join(*,G) from a CE, the RPF check is done
against the address of the corresponding RP; otherwise the procedure
is the same.
8.2.2. Data Plane RPF Check
Suppose a red default PMSI has been associated with a blue VRF, as
specified above, and an (S,G) multicast data packet is received from
the red default PMSI. Then S is looked up in the (blue) VRF. If it
matches a violet route, the packet is forwarded normally. However,
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if it matches a blue route, the packet is discarded as having failed
the RPF check.
This prevents the blue sites from receiving packets from red
transmitters, except in the case where routes to the red receivers
have been explicitly imported into the blue VRF.
8.3. Blue method
In the "blue method", extranet multicasts are carried by default in
the default PMSI of the blue VPN.
In the blue method, the red VRFs must be configured to import "blue"
I-PMSI and S-PMSI A-D routes. If MI-PMSIs are being used the P-
tunnels specified therein must be joined immediately. If MS-PMSIs
are being used, the P-tunnels need not be joined unless and until it
is necessary to send a PIM Join to the root of the P-tunnel.
The PIM C-instance associated with a red VRF will treat the red
default PMSI and the blue default PMSI as two different PIM
interfaces.
PIM Joins from blue receivers are then received at the red VRF over
the blue PMSI, whereas PIM Joins from red receivers are received at
the red VRF over the red PMSI. As a result, PIM may add one or the
other or both PMSIs to a particular multicast tree's olist.
In this method, the blue VRFs are associated with only one default
PMSI, so the RPF check for both blue and violet sources (and RPs)
always resolves to that PMSI. Hence the special RPF check procedures
of the red method are not necessary. However, a PE with a red VRF
may need to transmit multicast traffic on more than one MI-PMSI.
Note that since the data plane RPF check of section 8.2.2 is not
needed, one does not really need a "violet" RT value. Rather, one
may simply configure certain routes from the red VRF to be exported
with both the red and the blue RTs.
8.4. Binding Specific Extranet C-Flows to S-PMSIs
If the procedure of [MVPN] section 7.4.2 is used, the S-PMSI Join
message MUST be sent on whatever default PMSI or default PMSIs are
used to carry the C-flow identified in the message.
If the procedure of [MVPN]section 7.4.1 is used, then procedures
differ slightly depending upon whether the red method or the blue
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method is in use.
If the red method is in use, and if a C-flow whose target source is
exported from a red VRF is bound to an S-PMSI, then the S-PMSI A-D
route that specifies the binding must carry both the red RT and the
violet RT. Blue VRFs must be configured to import the violet S-PMSI
A-D routes.
If the blue method is in use, and if a C-flow whose target source is
exported from a red VRF is bound to an S-PMSI, then the S-PMSI A-D
route that specifies the binding:
- must carry the red RT if the C-flow has any receivers on the red
default PMSI, and
- must carry the blue RT if the C-flow has any receivers on the
blue default PMSI.
9. IANA Considerations
[MVPN] creates an IANA registry for the "S-PMSI Join Message Type
Field". This document requires three new values:
- The value 2 should be registered, and its description should read
"mLDP P2MP S-PMSI for IPv4 traffic (unaggregated)".
- The value 3 should be registered, and its description should read
"mLDP P2MP S-PMSI for IPv6 traffic (unaggregated)".
- The value 4 should be registered, and its description should read
"GRE S-PMSI for IPv6 traffic (unaggregated)".
10. Security Considerations
There are no additional security considerations beyond those of
[MVPN] and [MVPN-BGP].
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11. Authors' Addresses
Arjen Boers
Cisco Systems, Inc.
170 Tasman Drive
San Jose, CA, 95134
E-mail: aboers@cisco.com
Yiqun Cai
Cisco Systems, Inc.
170 Tasman Drive
San Jose, CA, 95134
E-mail: ycai@cisco.com
Eric C. Rosen
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA, 01719
E-mail: erosen@cisco.com
IJsbrand Wijnands
Cisco Systems, Inc.
De kleetlaan 6a Diegem 1831
Belgium
E-mail: ice@cisco.com
12. Normative References
[BIDIR-PIM] "Bidirectional Protocol Independent Multicast", Handley,
Kouvelas, Speakman, Vicisano, RFC 5015, October 2007
[MLDP] "Label Distribution Protocol Extensions for Point-to-
Multipoint and Multipoint-to-Multipoint Label Switched Paths", Minei,
Kompella, Wijnands, Thomas, draft-ietf-mpls-ldp-p2mp-05.txt, May 2008
[MVPN] "Multicast in MPLS/BGP IP VPNs", Rosen, Aggarwal, et. al.,
draft-ietf-l3vpn-2547bis-mcast-07.txt, June 2008
[MVPN-BGP] "BGP Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", Aggarwal, Rosen, Morin, Rekhter, Kodeboniya, draft-ietf-
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l3vpn-2547bis-mcast-bgp-05.txt, June 2008
[PIM] "Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", Fenner, Handley, Holbrook,
Kouvelas, RFC 4601, August 2006
[RFC2119] "Key words for use in RFCs to Indicate Requirement
Levels.", Bradner, March 1997
13. Informative References
[BSR] "Bootstrap Router (BSR) Mechanism for PIM", N. Bhaskar, et.al.,
RFC 5059, January 2008
14. Full Copyright Statement
Copyright (C) The IETF Trust (2008).
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contained in BCP 78, and except as set forth therein, the authors
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such proprietary rights by implementers or users of this
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Rosen, et al. [Page 22]