Internet DRAFT - draft-ietf-mpls-pim-sm-over-mldp
draft-ietf-mpls-pim-sm-over-mldp
Network Working Group Yakov Rekhter
Internet Draft Juniper Networks
Intended status: Standards Track
Expires: May 2015 Rahul Aggarwal
Arktan
Nicolai Leymann
Deutsche Telekom
Wim Henderickx
Alcatel-Lucent
Quintin Zhao
Huawei
Richard Li
Huawei
November 28, 2014
Carrying PIM-SM in ASM mode Trees over P2MP mLDP LSPs
draft-ietf-mpls-pim-sm-over-mldp-03.txt
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Abstract
When IP multicast trees created by PIM-SM in Any Source Multicast
(ASM) mode need to pass through an MPLS domain, it may be desirable
to map such trees to Point-to-Multipoint Label Switched Paths. This
document describes how to accomplish this in the case where such
Point-to-Multipoint Label Switched Paths are established using Label
Distribution Protocol Extensions for Point-to-Multipoint and
Multipoint-to-Multipoint Label Switched Paths Multipoint LDP (mLDP).
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Table of Contents
1 Introduction ................................................. 3
1.1 Specification of Requirements ................................ 5
2 Mechanism 1 - Non-transitive Mapping of IP Multicast Shared Trees 5
2.1 Originating Source Active Auto-Discovery Routes (Mechanism 1) .. 5
2.2 Receiving Source Active Auto-Discovery Route by LSR .......... 6
2.3 Handling (S, G, RPT-bit) State ............................... 6
3 Mechanism 2 - Transitive Mapping of IP Multicast Shared Tree ... 6
3.1 In-band Signaling for IP Multicast Shared Trees .............. 7
3.2 Originating Source Active Auto-Discovery Routes (Mechanism 2) .. 8
3.3 Receiving Source Active Auto-Discovery Route ................. 9
3.4 Pruning Sources Off the Shared Tree .......................... 9
3.5 More on Handling (S,G,RPT-bit) State ......................... 10
4 IANA Considerations .......................................... 10
5 Security Considerations ...................................... 10
6 Acknowledgements ............................................. 10
7 Normative References ......................................... 11
8 Informative References ....................................... 11
9 Authors' Addresses ........................................... 11
1. Introduction
[RFC6826] describes how to map Point-to-Multipoint Label Switched
Paths (P2MP LSPs) created by mLDP [RFC6388] to multicast trees
created by PIM-SM in Source-Specific Multicast (SSM) mode [RFC4607].
This document describes how to map mLDP P2MP trees to multicast trees
created by PIM-SM in Any-Source Multicast (ASM) mode. It describes
two possible mechanisms for doing this.
The first mechanism, described in Section 2, is OPTIONAL for
implementations, but the second mechanism, described in Section 3, is
REQUIRED for all implementations claiming conformance to this
specification.
Note that from a deployment point of view these two mechanisms are
mutually exclusive. That is on the same network one could deploy
either one of the mechanisms, but not both.
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The reader of this document is expected to be familiar with PIM-SM
[RFC4601] and mLDP [RFC6388].
This document relies on the procedures in [RFC6826] to support Source
Trees. E.g., following these procedures a Label Switching Router
(LSR) may initiate an mLDP Label Map with the Transit IPv4/IPv6
Source TLV for (S, G) when receiving a PIM (S,G) Join.
This document uses BGP Source Active auto-discovery routes, as
defined in [RFC6514]. For the sake of brevity in the rest of the
document we'll refer to these routes as just "Source Active auto-
discovery routes".
Consider a deployment scenario where the service provider has
provisioned the network in such a way that the Rendezvous Point (RP)
for a particular ASM group G is always between the receivers and the
sources. If the network is provisioned in this manner, the ingress PE
for (S,G) is always the same as the ingress PE for the RP, and thus
the Source Active auto-discovery (A-D) routes are never needed. If it
is known a priori that the network is provisioned in this manner,
mLDP in-band signaling can be supported using a different set of
procedures, as specified in [draft-wijnands]. A service provider will
provision the PE routers either to use [draft-wijnands] procedures or
to use the procedures of this document.
Like [RFC6826], each IP multicast tree is mapped one-to-one to a P2MP
LSP in the MPLS network. This type of service works well if the
number of LSPs that are created is under control of the MPLS network
operator, or if the number of LSPs for a particular service is known
to be limited.
It is to be noted that the existing BGP Multicast VPN (MVPN)
procedures [RFC6514] can be used to map Internet IP multicast trees
to P2MP LSPs. These procedures would accomplish this for IP
multicast trees created by PIM-SM in SSM mode as well as for IP
multicast trees created by PIM-SM in ASM mode. Furthermore, these
procedures would also support the ability to aggregate multiple IP
multicast trees to one P2MP LSP in the MPLS network. The details of
this particular approach are out of scope of this document.
This document assumes that a given LSR may have some of its
interfaces IP multicast capable, while other interfaces being MPLS
capable.
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1.1. 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 RFC 2119 [RFC2119].
2. Mechanism 1 - Non-transitive Mapping of IP Multicast Shared Trees
This mechanism does not transit IP multicast shared trees over the
MPLS network. Therefore, when an LSR creates (*, G) state (as a
result of receiving PIM messages on one of its IP multicast
interfaces), the LSR does not propagate this state in mLDP.
2.1. Originating Source Active Auto-Discovery Routes (Mechanism 1)
Whenever (as a result of receiving either PIM Register or MSDP
messages) an RP discovers a new multicast source, the RP SHOULD
originate a Source Active auto-discovery route. The route carries a
single MCAST-VPN Network Layer Reachability Information (NLRI)
[RFC6514] constructed as follows:
+ The Route Distinguisher (RD) in this NLRI is set to 0.
+ The Multicast Source field is set to S. This could be either an
IPv4 or an IPv6 address. The Multicast Source Length field is set
appropriately to reflect the address type.
+ The Multicast Group field is set to G. This could be either an
IPv4 or an IPv6 address. The Multicast Group Length field is set
appropriately to reflect this address type.
To constrain distribution of the Source Active auto-discovery route
to the AS of the advertising RP this route SHOULD carry the NO_EXPORT
Community ([RFC1997]).
Using the normal BGP procedures the Source Active auto-discovery
route is propagated to all other LSRs within the AS.
Whenever the RP discovers that the source is no longer active, the RP
MUST withdraw the Source Active auto-discovery route if such a route
was previously advertised by the RP.
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2.2. Receiving Source Active Auto-Discovery Route by LSR
Consider an LSR that has some of its interfaces capable of IP
multicast and some capable of MPLS multicast.
When as a result of receiving PIM messages on one of its IP multicast
interfaces an LSR creates in its Tree Information Base (TIB) a new
(*, G) entry with a non-empty outgoing interface list that contains
one or more IP multicast interfaces, the LSR MUST check if it has any
Source Active auto-discovery routes for that G. If there is such a
route, S of that route is reachable via an MPLS interface, and the
LSR does not have (S, G) state in its TIB for (S, G) carried in the
route, then the LSR originates the mLDP Label Map with the Transit
IPv4/IPv6 Source TLV carrying (S,G), as specified in [RFC6826].
When an LSR receives a new Source Active auto-discovery route, the
LSR MUST check if its TIB contains a (*, G) entry with the same G as
carried in the Source Active auto-discovery route. If such an entry
is found, S is reachable via an MPLS interface, and the LSR does not
have (S, G) state in its TIB for (S, G) carried in the route, then
the LSR originates an mLDP Label Map with the Transit IPv4/IPv6
Source TLV carrying (S,G), as specified in [RFC6826].
2.3. Handling (S, G, RPT-bit) State
Creation and deletion of (S, G, RPT-bit) PIM state ([RFC4601]) on an
LSR that resulted from receiving PIM messages on one of its IP
multicast interfaces does not result in any mLDP and/or BGP actions
by the LSR.
3. Mechanism 2 - Transitive Mapping of IP Multicast Shared Tree
This mechanism enables transit of IP multicast shared trees over the
MPLS network. Therefore, when an LSR creates (*, G) state as a result
of receiving PIM messages on one of its IP multicast interfaces, the
LSR propagates this state in mLDP, as described below.
Note that in the deployment scenarios where for a given G none of the
PEs originate an (S, G) mLDP Label Map with the Transit IPv4/IPv6
Source TLV, no Source Active auto-discovery routes will be used. One
other scenario where no Source Active auto-discovery routes will be
used is described in section "Originating Source Active Auto-
Discovery Routes (Mechanism 2)". In all these scenarios the only part
of Mechanism 2 that is used is the in-band signaling for IP Multicast
Shared Trees, as described in the next section.
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3.1. In-band Signaling for IP Multicast Shared Trees
To provide support for in-band mLDP signaling of IP multicast shared
trees this document defines two new mLDP TLVs: Transit IPv4 Shared
Tree TLV, and Transit IPv6 Shared Tree TLV.
These two TLVs have exactly the same encoding/format as the IPv4/IPv6
Source Tree TLVs defined in [RFC6826], except that instead of the
Source field they have an RP field that carries the address of the
RP, as follows:
Transit IPv4 Shared Tree TLV:
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 | RP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Group |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: TBD1 (to be assigned by IANA).
Length: 8
RP: IPv4 RP address, 4 octets.
Group: IPv4 multicast group address, 4 octets.
Transit IPv6 Shared Tree TLV:
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 | RP ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Group ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: TBD2 (to be assigned by IANA).
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Length: 32
RP: IPv6 RP address, 16 octets.
Group: IPv6 multicast group address, 16 octets.
Procedures for in-band signaling for IP multicast shared trees with
mLDP follow the same procedures as for in-band signaling for IP
multicast source trees specified in [RFC6826], except that while the
latter signals (S,G) state using Transit IPv4/IPv6 Source TLVs, the
former signals (*,G) state using Transit IPv4/IPv6 Shared Tree TLVs.
3.2. Originating Source Active Auto-Discovery Routes (Mechanism 2)
Consider an LSR that has some of its interfaces capable of IP
multicast and some capable of MPLS multicast.
Whenever such an LSR creates an (S, G) state as a result of receiving
an mLDP Label Map with the Transit IPv4/IPv6 Source TLV for (S, G)
the LSR MUST originate a Source Active auto-discovery route if all of
the following are true:
+ S is reachable via one of the IP multicast capable interfaces,
+ the LSR determines that G is in the PIM-SM in ASM mode range, and
+ the LSR does not have an (*, G) state with one of the IP
multicast capable interfaces as an incoming interface (iif) for
that state.
The route carries a single MCAST-VPN NLRI constructed as follows:
+ The RD in this NLRI is set to 0.
+ The Multicast Source field is set to S. The Multicast Source
Length field is set appropriately to reflect this address type.
+ The Multicast Group field is set to G. The Multicast Group Length
field is set appropriately to reflect this address type.
To constrain distribution of the Source Active auto-discovery route
to the AS of the advertising LSR this route SHOULD carry the
NO_EXPORT Community ([RFC1997]).
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Using the normal BGP procedures the Source Active auto-discovery
route is propagated to all other LSRs within the AS.
Whenever the LSR receiving an mLDP Label Map with the Transit
IPv4/IPv6 Source TLV for (S,G) deletes the (S,G) state that was
previously created, the LSR that deletes the state MUST also withdraw
the Source Active auto-discovery route, if such a route was
advertised when the state was created.
Note that whenever an LSR creates an (S,G) state as a result of
receiving an mLDP Label Map with the Transit IPv4/IPv6 Source TLV for
(S,G) with S reachable via one of the IP multicast capable
interfaces, and the LSR already has a (*,G) state with RP reachable
via one of the IP multicast capable interfaces as a result of
receiving an mLDP Label Map with the Transit IPv4/IPv6 Shared Tree
TLV for (*,G), the LSR does not originate a Source Active auto-
discovery route.
3.3. Receiving Source Active Auto-Discovery Route
Procedures for receiving Source Active Auto-Discovery routes are the
same as with Mechanism 1.
3.4. Pruning Sources Off the Shared Tree
If after receiving a new Source Active auto-discovery route for (S,G)
the LSR determines that (a) it has the (*, G) entry in its TIB, (b)
the incoming interface list (iif) for that entry contains one of the
IP interfaces, (c) at least one of the MPLS interfaces is in the
outgoing interface list (oif) for that entry, and (d) the LSR does
not originate an mLDP Label Mapping message for (S,G) with the
Transit IPv4/IPv6 Source TLV, then the LSR MUST transition the
(S,G,RPT-bit) downstream state to the Prune state. (Conceptually the
PIM state machine on the LSR will act "as if" it had received
Prune(S,G,rpt) on one of its MPLS interfaces, without actually having
received one.) Depending on the (S,G,RPT-bit) state on the iif, this
may result in the LSR using PIM procedures to prune S off the Shared
(*,G) tree.
The LSR MUST keep the (S,G,RPT-bit) downstream state machine in the
Prune state for as long as (a) the outgoing interface list (oif) for
(*, G) contains one of the MPLS interfaces, and (b) the LSR has at
least one Source Active auto-discovery route for (S,G), and (c) the
LSR does not originate the mLDP Label Mapping message for (S,G) with
the Transit IPv4/IPv6 Source TLV. Once either of these conditions
become no longer valid, the LSR MUST transition the (S,G,RPT-bit)
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downstream state machine to the NoInfo state.
Note that except for the scenario described in the first paragraph of
this section, it is sufficient to rely solely on the PIM procedures
on the LSR to ensure the correct behavior when pruning sources off
the shared tree.
3.5. More on Handling (S,G,RPT-bit) State
Creation and deletion of (S,G,RPT-bit) state on a LSR that resulted
from receiving PIM messages on one of its IP multicast interfaces
does not result in any mLDP and/or BGP actions by the LSR.
4. IANA Considerations
IANA maintains a registry called "Label Distribution Protocol (LDP)
Parameters" with a subregistry called "LDP MP Opaque Value Element
basic type". IANA is requested to allocate two new values as follows:
Value | Name | Reference
------+------------------------------+------------
TBD1 | Transit IPv4 Shared Tree TLV | [This.I-D]
TBD2 | Transit IPv6 Shared Tree TLV | [This.I-D]
IANA is requested to assign consecutive values.
5. Security Considerations
All the security considerations for mLDP ([RFC6388]) apply here.
From the security considerations point of view use of Shared Tree
TLVs is no different than use of Source TLVs [RFC6826].
6. Acknowledgements
Use of Source Active auto-discovery routes was borrowed from
[RFC6514]. Some text in this document was borrowed from [RFC6514].
Some of the text in this document was borrowed from [RFC6826].
We would like to acknowledge Arkadiy Gulko for his review and
comments.
We would also like to thank Xuxiaohu, Gregory Mirsky, Rajiv Asati,
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and Adrian Farrell for their review and comments.
7. Normative References
[RFC1997] R. Chandra, P. Traina, T. Li, "BGP Communities Attribute",
RFC1997, August 1996.
[RFC2119] "Key words for use in RFCs to Indicate Requirement
Levels.", Bradner, RFC2119, 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.
[RFC6388] Minei, I., "Label Distribution Protocol Extensions for
Point-to-Multipoint and Multipoint-to-Multipoint Label Switched
Paths", RFC6388, November 2011.
[RFC6514] "BGP Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", R. Aggarwal et al., RFC6514, February 2012
[RFC6826] "In-band signaling for Point-to-Multipoint and Multipoint-
to-Multipoint Label Switched Paths", I. Wijnands et al., RFC6826,
January 2013
8. Informative References
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, August 2006.
[draft-wijnands] Wijnands IJ, et. al., "mLDP In-Band Signaling with
Wildcards", draft-ietf-mpls-mldp-in-band-wildcard-encoding, work in
progress
9. Authors' Addresses
Yakov Rekhter
Juniper Networks, Inc.
e-mail: yakov@juniper.net
Rahul Aggarwal
e-mail: raggarwa_1@yahoo.com
Nicolai Leymann
Deutsche Telekom
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Winterfeldtstrasse 21
Berlin 10781
Germany
e-mail: nicolai.leymann@t-systems.com
Wim Henderickx
Alcatel-Lucent
Email: wim.henderickx@alcatel-lucent.com
Quintin Zhao
Huawei
Email: quintin.zhao@huawei.com
Richard Li
Huawei
Email: renwei.li@huawei.com
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