Internet DRAFT - draft-rosen-l3vpn-ir
draft-rosen-l3vpn-ir
L3VPN Working Group E. Rosen, Ed.
Internet-Draft Juniper Networks, Inc.
Updates: 6513,6514 (if approved) K. Subramanian
Intended status: Standards Track Cisco Systems, Inc.
Expires: April 18, 2015 J. Zhang
Juniper Networks, Inc.
October 15, 2014
Ingress Replication Tunnels in Multicast VPN
draft-rosen-l3vpn-ir-02
Abstract
RFCs 6513, 6514, and other RFCs describe procedures by which a
Service Provider may offer Multicast VPN service to its customers.
These procedures create point-to-multipoint (P2MP) or multipoint-to-
multipoint trees across the Service Provider's backbone. One type of
P2MP tree that may be used is known as an "Ingress Replication (IR)
tunnel". In an IR tunnel, a parent node need not be "directly
connected" to its child nodes. When a parent node has to send a
multicast data packet to its child nodes, it does not use layer 2
multicast, IP multicast, or MPLS multicast to do so. Rather, it
makes n individual copies, and then unicasts each copy, through an IP
or MPLS unicast tunnel, to exactly one child node. While the prior
MVPN specifications allow the use of IR tunnels, those specifications
are not always very clear or explicit about how the MVPN protocol
elements and procedures are applied to IR tunnels. This document
updates RFCs 6513 and 6514 by adding additional details that are
specific to the use of IR tunnels.
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
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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 April 18, 2015.
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Copyright Notice
Copyright (c) 2014 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. What is an IR P-tunnel? . . . . . . . . . . . . . . . . . . . 5
3. How are IR P-tunnels Identified? . . . . . . . . . . . . . . 6
4. How to Join an IR P-tunnel . . . . . . . . . . . . . . . . . 8
4.1. Advertised P-tunnels . . . . . . . . . . . . . . . . . . 9
4.1.1. If the 'Leaf Info Required Bit' is Set . . . . . . . 9
4.1.2. If the 'Leaf Info Required Bit' is Not Set . . . . . 10
4.2. Unadvertised P-tunnels . . . . . . . . . . . . . . . . . 10
5. The PTA's 'Tunnel Identifier' Field . . . . . . . . . . . . . 11
6. The PTA's 'MPLS Label' Field . . . . . . . . . . . . . . . . 11
6.1. Leaf A-D Route Originated by an Egress PE . . . . . . . . 12
6.2. Leaf A-D Route Originated by an Intermediate Node . . . . 13
6.2.1. Upstream and Downstream Segments are IR Segments . . 14
6.2.2. Only One Segment is IR . . . . . . . . . . . . . . . 14
6.3. Intra-AS I-PMSI A-D Route . . . . . . . . . . . . . . . . 15
7. How A Child Node Prunes Itself from an IR P-tunnel . . . . . 15
8. Parent Node Actions Upon Receiving Leaf A-D Route . . . . . . 16
9. Use of Timers when Switching UMH . . . . . . . . . . . . . . 17
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
12. Security Considerations . . . . . . . . . . . . . . . . . . . 18
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
13.1. Normative References . . . . . . . . . . . . . . . . . . 18
13.2. Informative References . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
RFCs 6513, 6514, and others describe procedures by which a Service
Provider (SP) may offer Multicast VPN (MVPN) service to its
customers. These procedures create point-to-multipoint (P2MP) or
multipoint-to-multipoint (MP2MP) tunnels, called "P-tunnels"
(Provider-tunnels), across the SP's backbone network. Customer
multicast traffic is carried through the P-tunnels.
A number of different P-tunnel technologies are supported. One of
the supported P-tunnel technologies is known as "ingress replication"
or "unicast replication". We will use the acronym "IR" to refer to
this P-tunnel technology.
An IR P-tunnel is a P2MP tree, but a given node on the tree is not
necessarily "directly attached" to its parent node or to its child
nodes. To send a multicast data packet from a parent node to one of
its child nodes, the parent node encapsulates the packet and then
unicasts it (through a P2P or MP2P MPLS LSP or a unicast IP tunnel)
to the child node. If a node on an IR tree has n child nodes, and
has a multicast data packet that must be sent along the tree, the
parent node makes n individual copies of the data packet, and then
sends each copy, through a unicast tunnel, to exactly one child node.
No lower layer multicast technology is used when sending traffic from
a parent node to a child node; multiple copies of the packet may
therefore be sent out a single interface.
With the single exception of IR, the P-tunnel technologies supported
by the MVPN specifications are pre-existing IP multicast or MPLS
multicast technologies. Each such technology has its own set of
specifications, its own setup and maintenance protocols, its own
syntax for identifying specific multicast trees, and its own
procedures for enabling a router to be added to or removed from a
particular multicast tree. For IR P-tunnels, on the other hand,
there is no prior specification for setting up and maintaining the
P2MP trees; the procedures and protocol elements used for setting up
and maintaining the P2MP trees are specified in the MVPN
specifications themselves, and all the signaling/setup is done by
using the BGP A-D (Auto-Discovery) routes that are defined in
[RFC6514]. (The unicast tunnels used to transmit multicast data from
one node to another in an IR P-tunnel may of course have their own
setup and maintenance protocols, e.g., [RFC5036], [RFC3209].)
Since the transmission of a multicast data packet along an IR
P-tunnel is done by transmitting the packet through a unicast tunnel,
previous RFCs sometimes speak of an IR P-tunnel as "consisting of" a
set of unicast tunnels. However, that way of speaking is not quite
accurate. For one thing, it obscures the fact that an IR P-tunnel is
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really a P2MP tree, whose nodes must maintain multicast state in both
the control and data planes. For another, it obscures the fact the
unicast tunnels used by a particular IR P-tunnel need not be specific
to that P-tunnel; a single unicast tunnel can carry the multicast
traffic of many different IR P-tunnels (and can also carry unicast
traffic as well).
In this document, we provide a clearer and more explicit conceptual
model for IR P-tunnels, clarifying the relationship between an IR
P-tunnel and the unicast tunnels that are used for data transmission
along the IR P-tunnel.
RFC 6514 defines a protocol element called a "tunnel identifier",
which for most P-tunnel technologies is used to identify a P-tunnel
(i.e., to identify a P2MP or MP2MP tree). However, when IR P-tunnels
are used, this protocol element does not identify an IR P-tunnel. In
some cases it identifies one of the P-tunnel's constituent unicast
tunnels, and in other cases it is not used to identify a tunnel at
all. In this document, we provide an explicit specification for how
IR P-tunnels are actually identified.
Some of the MVPN specifications use phrases like "join the identified
P-tunnel", even though there has up to now not been an explicit
specification of how to identify an IR P-tunnel, of how a router
joins such a P-tunnel, or of how a router prunes itself from such a
P-tunnel. In this document, we make these procedures more explicit.
RFC 6514 does provide a method for binding an MPLS label to a
P-tunnel, but does not discuss the label allocation policies that are
needed for correct operation when the P-tunnel is an IR P-tunnel.
Those policies are discussed in this document.
This document does not provide any new protocol elements or
procedures; rather it makes explicit just how a router is to use the
protocol elements and procedures of [RFC6513] and [RFC6514] to
identify an IR P-tunnel, to join an IR P-tunnel, and to prune itself
from an IR P-tunnel. This document also discusses the MPLS label
allocation policies that need to be supported when binding MPLS
labels to IR P-tunnels, and the timer policies that need to be
supported when switching a customer multicast flow from one P-tunnel
to another. As the material in this document must be understood in
order to properly implement IR P-tunnels, this document is considered
to update [RFC6513] and [RFC6514]. This document also discusses the
application of "seamless multicast" [SMLS-MC] and "extranet" [MVPN-
XNET] procedures to IR P-tunnels.
This draft does not discuss the use of IR P-tunnels to support a VPN
customer's use of BIDIR-PIM. [C-BIDIR-IR] explains how to adapt the
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procedures of [RFC6513], [RFC6514], and [MVPN-BIDIR] so that a
customer's use of BIDIR-PIM can be supported by IR P-tunnels.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL", when and only when appearing in all capital letters, are
to be interpreted as described in [RFC2119].
2. What is an IR P-tunnel?
An IR P-tunnel is a P2MP tree. Its nodes are BGP speakers that
support the MVPN procedures of [RFC6514] and related RFCs. In
general, the nodes of an IR P-tunnel are either PE routers, ASBRs, or
(if [SMLS-MC] is supported) ABRs. (MVPN procedures are sometimes
used to support non-MVPN, or "global table" multicast; one way of
doing this is defined in [SMLS-MC]. In such a case, IR P-tunnels can
be used outside the context of MVPN.)
MVPN P-tunnels may be either "segmented" or "non-segmented" (as these
terms are defined in [RFC6513] and [RFC6514]).
A "non-segmented" IR P-tunnel is a two-level P2MP tree, consisting
only of a root node and a set of nodes that are children of the root
node. When used in an MVPN context, the root is an ingress PE, and
the child nodes of the root are the egress PEs.
In a segmented P-tunnel, IR may be used for some or all of the
segments. If a particular segment of a segmented P-tunnel uses IR,
then the root of that segment may have child nodes that are ABRs or
ASBRs, rather than egress PEs.
As with any type of P2MP tree, each node of an IR P-tunnel holds
"multicast state" for the P-tunnel. That is, each node knows the
identity of its parent node on the tree, and each node knows the
identities of its child nodes on the tree. In the MVPN specs, the
"parent" node is also known as the "Upstream Multicast Hop" or "UMH".
What distinguishes an IR P-tunnel from any other kind of P2MP tree is
the method by which a data packet is transmitted from a parent node
to a child node. To transmit a multicast data packet from a parent
node to a child node along a particular IR P-tunnel, the parent node
does the following:
o It labels the packet with a label (call it a "P-tunnel label")
that the child node has assigned to that P-tunnel,
o It then places the packet in a unicast encapsulation and unicasts
the packet to the child node. That is, the parent node sends the
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packet through a "unicast tunnel" to a particular child node.
This unicast tunnel need not be specially created to be part of
the IR P-tunnel; it can be any P2P or MP2P unicast tunnel that
will get the packets from the parent node to the child node. A
single such unicast tunnel may be carrying multicast data packets
of several different P2MP trees, and may also be carrying unicast
data packets.
The parent node repeats this process for each child node, creating
one copy for each child node, and sending each copy through a unicast
tunnel to corresponding child node. It does not use layer 2
multicast, IP multicast, or MPLS multicast to transmit packets to its
child nodes. As a result, multiple copies of each packet may be sent
out a single interface; this may happen, e.g., if that interface is
the next hop interface, according to unicast routing, from the parent
node to several of the child nodes.
Since data traveling along an IR P-tunnel is always unicast from
parent node to child node, it can be convenient to think of an IR
P-tunnel as a P2MP tree whose arcs are unicast tunnels. However, it
is important to understand that the unicast tunnels need not be
specific to any particular IR P-tunnel. If R1 is the parent node of
R2 on two different IR P-tunnels, a single unicast tunnel from R1 to
R2 may be used to carry data along both IR P-tunnels. All that is
required is that when the data packets arrive at R2, R2 will see the
"P-tunnel label" at the top of the packets' label stack; R2's further
processing of the packets will depend upon that label. Note that the
same unicast tunnel between R1 and R2 may also be carrying unicast
data packets.
Typically the unicast tunnels are the Label Switched Paths (LSPs)
that already exist to carry unicast traffic; either MP2P LSPs created
by LDP [RFC5036] or P2P LSPs created by RSVP-TE [RFC3209]. However,
any other kind of unicast tunnel may be used. A unicast tunnel may
have an arbitrary number of intermediate routers; those routers do
not maintain any multicast state for the IR P-tunnel, and in general
are not even aware of its existence.
As with all other P-tunnel types, IR P-tunnels may be used as
Inclusive P-tunnels or as Selective P-tunnels.
3. How are IR P-tunnels Identified?
There are four MVPN BGP route types in which P-tunnels can be
identified: Intra-AS I-PMSI A-D routes, Inter-AS I-PMSI A-D routes,
S-PMSI A-D routes, and Leaf A-D routes. (These route types are all
defined in [RFC6514]).
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Whenever it is necessary to identify a P-tunnel in a route of one of
these types, a "PMSI Tunnel Attribute" (PTA) is added to the route.
As defined in [RFC6514] section 5, the PTA contains four fields:
"Tunnel Type", "MPLS Label", "Tunnel Identifier", and "Flags".
[RFC6514] defines only one bit in the "Flags" field, the "Leaf
Information Required" bit.
If a route identifies an IR P-tunnel, the "Tunnel Type" field of its
PTA is set to the value 6, meaning "Ingress Replication".
Most types of P-tunnel are associated with specific protocols that
are used to set up and maintain tunnels of that type. For example,
if the "Tunnel Type" field is set to 2, meaning "mLDP P2MP LSP", the
associated setup protocol is mLDP [mLDP]. The associated setup
protocol always has a method of identifying the tunnels that it sets
up. For example, mLDP uses a "FEC element" to identify a tree. If
the "Tunnel type" field is set to 3, meaning "PIM SSM Tree", the
associated setup protocol is PIM, and "(S,G)" is used to identify the
tree. In these cases, the "Tunnel Identifier" field of the PTA
carries a tree identifier as defined by the setup protocol used for
the particular tunnel type.
IR P-tunnels, on the other hand, are entirely setup and maintained by
the use of BGP A-D routes, and are not associated with any other
setup protocol. (The unicast tunnels used to transmit multicast data
along an IR P-tunnel may have their own setup and maintenance
protocols, of course.) Further, the identifier of an IR P-tunnel
does not appear in the PTA at all. Rather, the P-tunnel identifier
is in the "Network Layer Reachability Information" (NLRI) field of
the A-D routes that are used to advertise and to setup the P-tunnel.
When an IR P-tunnel is identified in an S-PMSI A-D route, an Intra-AS
I-PMSI A-D route, or an Inter-AS I-PMSI A-D route (we will refer to
these three route types as "advertising A-D routes"), its identifier
is hereby defined to be the NLRI of that route. See sections 4.1,
4.2, and 4.3 of [RFC6514] for the specification of these NLRIs. Note
that the P-tunnel identifier includes the "route type" and "length"
octets of the NLRI.
An advertising A-D route is considered to identify an IR P-tunnel
only if it carries a PTA whose "Tunnel Type" field is set to "IR".
When an IR P-tunnel is identified in an S-PMSI A-D route or in an
Inter-AS I-PMSI A-D route, the "Leaf Info Required" bit of the Flags
field of the PTA MUST be set.
In an advertising A-D route:
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o If the "Leaf Info Required" bit of the Flags field of the PTA is
set, then the "Tunnel Identifier" field of the PTA has no
significance whatsoever, and MUST be ignored upon reception.
Note that, per RFC6514, the length of the "Tunnel Identifier"
field is variable, and is inferred from the length of the PTA.
Even when this field is of no significance, its length MUST be the
length of an IP address in the address space of the SP's backbone,
as specified in section 4.2 of [RFC6515]. In this case, it is
RECOMMENDED that it be set to a routable address of the router
that constructed the PTA. (While it might make more sense to
allow or even require the field to be omitted entirely, that might
raise issues of backwards compatibility with implementations that
were designed prior to the publication of this document.)
o If the "Leaf Info Required" bit is not set, the "Tunnel
Identifier" field of the PTA does have significance, but it does
not identify the IR P-tunnel. The use of the PTA's "Tunnel
Identifier" field in this case is discussed in Section 5 of this
document.
Note that according to the above definition, there is no way for two
different advertising A-D routes (i.e., two advertising A-D routes
with different NLRIs) to advertise the same IR P-tunnel. In the
terminology of [RFC6513], an IR P-tunnel can instantiate only a
single PMSI. If an ingress PE, for example, wants to bind two
customer multicast flows to a single IR P-tunnel, it must advertise
that tunnel in an I-PMSI A-D route or in an S-PMSI A-D route whose
NLRI contains wildcards ([RFC6625]).
When an IR P-tunnel is identified in a Leaf A-D route, its identifier
is the "route key" field of the route's NLRI. See section 4.4 of
[RFC6514].
A Leaf A-D route is considered to identify an IR P-tunnel only if it
carries a PTA whose "Tunnel Type" field is set to "IR". In this type
of route, the "Tunnel Identifier" field of the PTA does have
significance, but it does not identify the IR P-tunnel. The use of
the PTA's "Tunnel Identifier" field in this case is discussed in
Section 5.
4. How to Join an IR P-tunnel
The procedures for joining an IR P-tunnel depend upon whether the
P-tunnel has been previously advertised, and if so, upon how the
P-tunnel was advertised. Note that joining an unadvertised P-tunnel
is only possible when using the "Global Table Multicast" procedures
of [SMLS-MC].
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4.1. Advertised P-tunnels
The procedures in this section apply when the P-tunnel to be joined
has been advertised in an S-PMSI A-D route, an Inter-AS I-PMSI A-D
route, or an Intra-AS I-PMSI A-D route.
The procedures for joining an advertised IR P-tunnel depend upon
whether the A-D route that advertises the P-tunnel has the "Leaf Info
Required" bit set in its PTA.
4.1.1. If the 'Leaf Info Required Bit' is Set
The procedures in this section apply when the P-tunnel to be joined
has been advertised in a route whose PTA has the "Leaf Info Required
Bit" set.
The router joining a particular IR P-tunnel must determine its UMH
for that P-tunnel. If the route that advertised the P-tunnel
contains a P2MP Segmented Next Hop Extended Community, the UMH is
determined from the value of this community (see [SMLS-MC]).
Otherwise the UMH is determined from the route's next hop (see
[RFC6514]).
Once the UMH is determined, the router joining the IR P-tunnel
originates a Leaf A-D route. The NLRI of the Leaf A-D route MUST
contain the tunnel identifier (as defined in Section 3 above) as its
"route key". The UMH MUST be identified by attaching an "IP Address
Specific Route Target" (or an "IPv6 Address Specific Route Target")
to the Leaf A-D route. The IP address of the UMH appears in the
"global administrator" field of the Route Target (RT). Details can
be found in [RFC6514] and [SMLS-MC].
The Leaf A-D route MUST also contain a PTA whose fields are set as
follows:
o The "Tunnel Type" field is set to "IR".
o The "Tunnel Identifier" field is set as described in Section 5 of
this document.
o The "MPLS Label" field is set to a non-zero value. This is the
"P-tunnel label". The value must be chosen so as to satisfy
various constraints, as discussed in Section 6 this document.
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4.1.2. If the 'Leaf Info Required Bit' is Not Set
The procedures in this section apply when the P-tunnel to be joined
has been advertised in a route whose PTA does not have the "Leaf Info
Required Bit" set. This can only be the case if the P-tunnel was
advertised in an Intra-AS I-PMSI A-D route.
If an IR P-tunnel is advertised in the Intra-AS I-PMSI A-D routes
originated by the PE routers of a given MVPN, the Intra-AS I-PMSI can
be thought of as being instantiated by a set of IR P-tunnels. Each
PE is the root of one such P-tunnel, and the other PEs are children
of the root. A PE simultaneously joins all these P-tunnels by
originating (if it hasn't already done so) an Intra-AS I-PMSI A-D
route with a PTA whose fields are set as follows:
o The "Tunnel Type" field is set to "IR".
o The "Tunnel Identifier" field is set as described in Section 5 of
this document.
o The "MPLS Label" field MUST be set to a non-zero value. This
label value will be used by the child node to associate a received
packet with the I-PMSI of a particular MVPN. The MPLS label
allocation policy must be such as to ensure that the binding from
label to I-PMSI is one-to-one.
The NLRI and the RTs of the originated I-PMSI A-D route are set as
specified in [RFC6514].
Note that if a set of IR P-tunnels is joined in this manner, the
"discard from the wrong PE" procedures of [RFC6513] section 9.1.1
cannot be applied to that P-tunnel. Thus duplicate prevention on
such IR P-tunnels requires the use of either Single Forwarder
Selection ([RFC6513] section 9.1.2) or native PIM procedures
([RFC6513] section 9.1.3).
4.2. Unadvertised P-tunnels
In [SMLS-MC], a procedure is defined for "Global Table Multicast", in
which a P-tunnel can be joined even if the P-tunnel has not been
previously advertised. See the sections of that document entitled
"Leaf A-D Route for Global Table Multicast" and "Constructing the
Rest of the Leaf A-D Route". The route key of the Leaf A-D route has
the form of the "S-PMSI Route-Type Specific NLRI" in this case, and
that should be considered to be the P-tunnel identifier. Note that
the procedure for finding the UMH is different in this case; the UMH
is the next hop of the best UMH-eligible route towards the "ingress
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PE". See the section of that document entitled "Determining the
Upstream ABR/PE/ASBR (Upstream Node)".
5. The PTA's 'Tunnel Identifier' Field
If the "Tunnel Type" field of a PTA is set to "IR", its "Tunnel
Identifier" field is significant only when one of the following two
conditions holds:
o The PTA is carried by a Leaf A-D route, or
o The "Leaf Information Required" bit of the "Flags" field of the
PTA is not set.
If one of these conditions holds, then the "Tunnel Identifier" field
must contain a routable IP address of the originator of the route.
(See [RFC6514] sections 9.2.3.2.1 and 9.2.3.4.1 for the detailed
specification of the contents of this field.) This address is used
by the UMH to determine the unicast tunnel that it will use in order
to send data, along the IR P-tunnel identified by the route key, to
the originator of the Leaf A-D route.
The means by which the unicast tunnel is determined from this IP
address is outside the scope of this document. The means by which
the unicast tunnel is set up and maintained is also outside the scope
of this document.
Section 4 of [RFC6515] MUST be applied when a PTA is carried in a
Leaf A-D route, and describes how to determine whether the "Tunnel
Identifier" field carries an IPv4 or an IPv6 address.
If neither of the above conditions hold, then the "Tunnel Identifier"
field is of no significance, and MUST be ignored upon reception.
6. The PTA's 'MPLS Label' Field
When a PTA is carried by an S-PMSI A-D route or an Inter-AS I-PMSI
A-D route, and the "Tunnel Type" field is set to "IR", the "MPLS
Label" field is of no significance. In this case, it SHOULD be set
to zero upon transmission and MUST be ignored upon reception.
The "MPLS Label" field is significant only when the PTA appears
either in a Leaf A-D route or in an Intra-AS I-PMSI A-D route that
does not have the "Leaf Information Required" bit set. In these
cases, the MPLS label is the label that the originator of the route
is assigning to the IR P-tunnel(s) identified by the route's NLRI.
(That is, the MPLS label assigned in the PTA is what we have called
the "P-tunnel label".)
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6.1. Leaf A-D Route Originated by an Egress PE
As previously stated, when a Leaf A-D route is used to join an IR
P-tunnel, the "route key" of the Leaf A-D route is the P-tunnel
identifier.
We now define the notion of the "root of an IR P-tunnel".
o If the identifier of an IR P-tunnel is of the form of an S-PMSI
NLRI, the "root" of the P-tunnel is the router identified in the
"Originating Router's IP Address" field of that NLRI.
o If the identifier of an IR P-tunnel is of the form specified in
Section "Leaf A-D Route for Global Table Multicast" of [SMLS-MC],
the "root" of the P-tunnel is the router identified in the
"Ingress PE's IP Address" field of that NLRI.
o If the identifier of an IR P-tunnel is of the form of an Intra-AS
I-PMSI NLRI, the "root" of the P-tunnel is the router identified
in the "Originating Router's IP Address" field of that NLRI.
o If the identifier of an IR P-tunnel is of the form of an Inter-AS
I-PMSI NLRI, the "root" of the P-tunnel is same as the identifier
of the P-tunnel, i.e., the combination of an RD and an AS.
Note that if a P-tunnel is segmented, the root of the P-tunnel, by
this definition, is actually the root of the entire P-tunnel, not the
root of the local segment.
In order to apply the procedures of RFC 6513 Section 9.1.1
("Discarding Packets from Wrong PE"), the following condition MUST be
met by the MPLS label allocation policy:
Suppose an egress PE originates two Leaf A-D routes, each with a
different route key in its NLRI, and each with a PTA specifying a
"Tunnel Type" of "IR". Thus each of the Leaf A-D routes
identifies a different IR P-tunnel. Suppose further that each of
those IR P-tunnels has a different root. Then the egress PE MUST
NOT specify the same MPLS label in both PMSI Tunnel attributes.
That is, to apply the "Discarding Packets from the Wrong PE"
duplicate prevention procedures ([RFC6513] section 9.1.1), the same
MPLS label MUST NOT be assigned to two IR P-tunnels that have
different roots.
If segmented P-tunnels are in use, the above rule is necessary but
not sufficient to prevent a PE from forwarding duplicate data to the
CEs. For various reasons, a given egress PE or egress ABR or egress
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ASBR may decide to change its parent node, on a given segmented
P-tunnel, from one router to another. It does this by changing the
RT of the Leaf A-D route that it originated in order to join that
P-tunnel. Once the RT is changed, there may be a period of time
during which the old parent node and the new parent node are both
sending data of the same multicast flow. To ensure that the egress
node not forward duplicate data, whenever the egress node changes the
RT that it attaches to a Leaf A-D route, it MUST also change the
"MPLS Label" specified in the Leaf A-D route's PTA. This allows the
egress router to distinguish between packets arriving on a given
P-tunnel from the old parent and packets arriving on that same
P-tunnel from the new parent. At any given time, a router MUST
consider itself to have only a single parent node on a given
P-tunnel, and MUST discard traffic that arrives on that P-tunnel from
a different parent node.
If extranet functionality [MVPN-XNET] is not implemented in a
particular egress PE, or if an egress PE is provisioned with the
knowledge that extranet functionality is not needed, the PE may adopt
the policy of assigning a label that is unique for the ordered triple
<root, parent node, egress VRF>. This will enable the egress PE to
apply the duplicate prevention procedures discussed above, and to
determine the VRF to which an arriving packet must be directed.
However, this policy is not sufficient to support the "Discard
Packets from the Wrong P-tunnel" procedures that are specified in
[MVPN-XNET]. To support those procedures, the labels specified in
the PTA of Leaf A-D routes originated by a given egress PE MUST be
unique for the ordered triple <root, root RD, parent node>, where the
"root RD" is taken from the RD field of the IR P-tunnel identifier.
(All forms of IR P-tunnel identifier contain an embedded "RD" field.)
This policy is also sufficient for supporting non-extranet cases, but
in some cases may result in the use of more labels than the policy of
the previous paragraph.
6.2. Leaf A-D Route Originated by an Intermediate Node
When a P-tunnel is segmented, there will be "intermediate nodes"
(nodes that have a parent and also have children on the P-tunnel).
Each intermediate node is a leaf node of an "upstream segment" and a
parent node of a "downstream segment". The intermediate node
"splices" together the two segments, so that data it receives on the
upstream segment gets transmitted on the downstream segment. If
either the upstream or downstream segments (or both) are instantiated
by IR, the need to do this splicing places certain constraints on the
MPLS label allocation policy.
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6.2.1. Upstream and Downstream Segments are IR Segments
An intermediate node N (i.e., a node that has a parent and also has
children) on an IR P-tunnel may originate a Leaf A-D route with a
particular route key as a result of receiving a Leaf A-D route with
that same route key. This will happen only if the received Leaf A-D
route carries an IP address specific RT whose Global Administrator
field identifies node N.
Suppose intermediate node N originates two Leaf A-D routes, one whose
route key is K1, and one whose route key is K2, where K1 != K2. In
general, the respective PTAs of these Leaf A-D routes MUST specify
distinct non-zero MPLS labels, such that it is possible to map
uniquely from the specified label value to a single IR P-tunnel (call
this the "uniqueness rule"). There is one exception to this rule;
the exception is specified below.
Consider the set of Leaf A-D routes with route key K1 or route key K2
such that:
o N has received these Leaf A-D routes and has them currently
installed.
o Each of these Leaf A-D routes carries an IP Address Specific Route
Target that identifies N in its Global Administrator field.
Now suppose that all the Leaf A-D routes in this set have the same
originating router, and that the PTAs of these Leaf A-D routes all
specify the same MPLS label. Suppose further that N's UMH for K1 is
the same as N's UMH for K2. In this particular case, N MAY specify
the same MPLS label in the PTA of Leaf A-D route it originates for K1
as in the PTA of he route it originates for K2. However, if at any
future time these conditions no longer hold, N must reoriginate at
least one of the Leaf A-D routes with a different label so that the
"uniqueness rule" holds.
6.2.2. Only One Segment is IR
To handle the case where an intermediate node, call it N, is splicing
together two P-tunnel segments, only one of which is IR, it is
necessary to generalize the rules of the preceding sub-section.
Suppose N is a leaf node of two (upstream) P-tunnel segments, call
them U1 and U2. Suppose also that N is a parent node of two
(downstream) P-tunnel segments, call them D1 and D2. And suppose
that N needs to splice U1 to D1, and U2 to D2.
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To follow the uniqueness rule of Section 6.2.1 of this document, N
must assign a different MPLS label to U1 than it assigns to U2. How
this assignment is made depends, of course, on the control protocol
used to set up U1 and U2.
There is one case in which the uniqueness rule need not be followed.
Suppose that there is a node M such that (a) M is N's only child node
on D1, and (b) M is N's only child node on D2. M will have
advertised to N a label L1 bound to D1, and a label L2 bound to D2.
If (and for as long as) L1==L2, then N MAY violate the uniqueness
rule by advertising to its parent node for U1 the same MPLS label it
advertises to its parent node for U2.
Section 6.2.1 of this document specifies in detail the way this
requirement is applied when the upstream and downstream segments are
all IR segments.
6.3. Intra-AS I-PMSI A-D Route
When a router joins a set of IR P-tunnels using the procedures of
Section 4.1.2 of this document, the procedures of section 9.1.1 of
[RFC6513] cannot be applied, no matter what the label allocation
policy is. In this case, the ingress PE is the same as the UMH, but
it is not possible to assign a label uniquely to a particular ingress
PE or UMH. However, the label in the MPLS label field of the PTA
MUST NOT appear in the MPLS label field of the PTA carried by any
other route originated by the same router.
7. How A Child Node Prunes Itself from an IR P-tunnel
If a particular IR P-tunnel was joined via the procedures of
Section 4.1.2 of this document, a router can prune itself from the
P-tunnel by withdrawing the Intra-AS I-PMSI A-D route it used to join
the P-tunnel. This is not usually done unless the router is removing
itself entirely from a particular MVPN.
The procedures in the remainder of this section apply when a router
joined a particular IR P-tunnel by originating a Leaf A-D route (as
described in Section 4.1.1 or Section 4.2 of this document).
If a router no longer has a need to receive any multicast data from a
given IR P-tunnel, it may prune itself from the P-tunnel by
withdrawing the Leaf A-D route it used to join the tunnel. This is
done, e.g., if the router no longer needs any of the flows traveling
over the P-tunnel, or if all the flows the router does need are being
received over other P-tunnels.
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A router that is attached to a particular IR P-tunnel via a
particular parent node may determine that it needs to stay joined to
that P-tunnel, but via a different parent node. This can happen, for
example, if there is a change in the Next Hop or the P2MP Segmented
Next Hop Extended Community of the S-PMSI A-D route in which that
P-tunnel was advertised. In this case, the router changes the Route
Target of the Leaf A-D route it used to join the IR P-tunnel, so that
the Route Target now identifies the new parent node.
A parent node must notice when a child node has been pruned from a
particular tree, as this will affect the parent node's multicast data
state. Note that the pruning of a child node may appear to the
parent node as the explicit withdrawal of a Leaf A-D route, or it may
appear as a change in the Route Target of a Leaf A-D route. If the
Route Target of a particular Leaf A-D route previously identified a
particular parent node, but changes so that it no longer does so, the
effect on the multicast state of the parent node is the same as if
the Leaf A-D route had been explicitly withdrawn.
8. Parent Node Actions Upon Receiving Leaf A-D Route
These actions are detailed in [RFC6514] and [SMLS-MC]. Two points of
clarification are made:
o If a router R1 receives and installs a Leaf A-D route originated
by router R2, R1's multicast state is affected only if the Leaf
A-D route carries an "IP Address Specific RT" (or "IPv6 Address
Specific RT") whose "global administrator" field identifies R1.
(This is as specified in [RFC6514] and [SMLS-MC].) If a Leaf A-D
route's RT does not identify R1, but then changes so that it does
identify R1, R1 must take the same actions it would take if the
Leaf A-D route were newly received.
o It is possible that router R1 will receive and install a Leaf A-D
route originated by router R2, where:
* the route's RT identifies R1,
* the route's NLRI contains a route key whose first octet
indicates that it is identifying a P-tunnel advertised in an
S-PMSI A-D route,
* R1 has neither originated nor installed any such S-PMSI A-D
route.
If at some later time, R1 installs the corresponding S-PMSI A-D
route, and the Leaf A-D route is still installed, and the Leaf A-D
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route's RT still identifies R1, then R1 MUST follow the same
procedures it would have followed if the S-PMSI A-D route had been
installed before the Leaf A-D route was installed. (I.e.,
implementers must not assume that events occur in the "usual" or
"expected" order.)
9. Use of Timers when Switching UMH
Suppose a child node has joined a particular IR P-tunnel via a
particular UMH, and it now determines (for whatever reason) that it
needs to change its UMH on that P-tunnel. It does this by modifying
the RT of a Leaf A-D route.
It is desirable for such a "switch of UMH" to be done using a "make
before break" technique, so that the older UMH does not stop
transmitting the packets on the given P-tunnel to the child until the
newer UMH has a chance to start transmitting the packets on the given
P-tunnel to the child. However, the control plane operation
(modifying the RT of the Leaf A-D route) does not permit the child
node to first join the P-tunnel at the new UMH, and then later prune
itself from the old UMH; a single control plane operation has both
effects. Therefore, to achieve "make before break", timers must be
used as follows:
1. The old UMH must continue transmitting to the child node for a
period of time after it sees the child's Leaf A-D route being
withdrawn (or its RT changing to identify a different UMH).
2. The child node must continue to accept packets from the old UMH
for a period of time before it starts to accept packets from the
new UMH (and discard packets from the old).
Further, the timer in 1 should be longer than the timer in 2. This
allows the child to switch from one UMH to another without any loss
of data.
10. IANA Considerations
This document contains no actions for IANA.
11. Acknowledgments
The authors wish to thank Yakov Rekhter for his contributions to this
work. We also wish to thank Huajin Jeng and Samir Saad for their
contributions, and to thank Thomas Morin for pointing out some of the
issues that needed further elaboration.
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Section 6.1 discusses the importance of having an MPLS label
allocation policy that, when ingress replication is used, allows an
egress PE to infer the identity of a received packet's ingress PE.
This issue was first raised in earlier work by Xu Xiaohu.
12. Security Considerations
No security considerations are raised by this document beyond those
already discussed in [RFC6513] and [RFC6514].
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6513] Rosen, E. and R. Aggarwal, "Multicast in MPLS/BGP IP
VPNs", RFC 6513, February 2012.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, February 2012.
[RFC6515] Aggarwal, R. and E. Rosen, "IPv4 and IPv6 Infrastructure
Addresses in BGP Updates for Multicast VPN", RFC 6515,
February 2012.
13.2. Informative References
[C-BIDIR-IR]
Zhang, J., Rekhter, Y., and A. Dolganow, "Simulating
'Partial Mesh of MP2MP P-Tunnels' with Ingress
Replication", internet-draft draft-ietf-l3vpn-mvpn-bidir-
ingress-replication-01, July 2014.
[MVPN-BIDIR]
Rosen, E., Wijnands, IJ., Cai, Y., and A. Boers, ""MVPN:
Using Bidirectional P-Tunnels", internet-draft draft-ietf-
l3vpn-mvpn-bidir-08, June 2014.
[MVPN-XNET]
Rekhter, Y. and E. Rosen, "Extranet Multicast in BGP/IP
MPLS VPNs", internet-draft draft-ietf-l3vpn-mvpn-extranet-
05, July 2014.
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[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
[RFC6625] Rosen, E., Rekhter, Y., Hendrickx, W., and R. Qiu,
"Wildcards in Multicast VPN Auto-Discovery Routes", RFC
6625, May 2012.
[SMLS-MC] Rekhter, Y., Aggarwal, R., Morin, T., Grosclaude, I.,
Leymann, N., and S. Saad, "Inter-Area P2MP Segmented
LSPs", internet-draft draft-ietf-mpls-seamless-mcast-14,
June 2014.
Authors' Addresses
Eric C. Rosen (editor)
Juniper Networks, Inc.
10 Technology Park Drive
Westford, Massachusetts 01886
US
Email: erosen@juniper.net
Karthik Subramanian
Cisco Systems, Inc.
170 Tasman Drive
San Jose, California 95134
US
Email: kartsubr@cisco.com
Jeffrey Zhang
Juniper Networks, Inc.
10 Technology Park Drive
Westford, Massachusetts 01886
US
Email: zzhang@juniper.net
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