Network Working Group IJ. Wijnands, Ed.
Internet-Draft T. Eckert
Intended status: Standards Track Cisco Systems, Inc.
Expires: June 3, 2012 N. Leymann
Deutsche Telekom
M. Napierala
AT&T Labs
December 1, 2011
Multipoint LDP in-band signaling for Point-to-Multipoint and Multipoint-
to-Multipoint Label Switched Paths
draft-ietf-mpls-mldp-in-band-signaling-05
Abstract
Consider an IP multicast tree, constructed by Protocol Independent
Multicast (PIM), needs to pass through an MPLS domain in which
Multipoint LDP (mLDP) Point-to-Multipoint and/or Multipoint-to-
Multipoint Labels Switched Paths (LSPs) can be created. The part of
the IP multicast tree that traverses the MPLS domain can be
instantiated as a multipoint LSP. When a PIM Join message is
received at the border of the MPLS domain, information from that
message is encoded into mLDP messages. When the mLDP messages reach
the border of the next IP domain, the encoded information is used to
generate PIM messages that can be sent through the IP domain. The
result is an IP multicast tree consisting of a set of IP multicast
sub-trees that are spliced together with a multipoint LSP.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 3, 2012.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Conventions used in this document . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. In-band signaling for MP LSPs . . . . . . . . . . . . . . . . 5
2.1. Transiting Unidirectional IP multicast Shared Trees . . . 6
2.2. Transiting IP multicast source trees . . . . . . . . . . . 7
2.3. Transiting IP multicast bidirectional trees . . . . . . . 7
3. LSP opaque encodings . . . . . . . . . . . . . . . . . . . . . 8
3.1. Transit IPv4 Source TLV . . . . . . . . . . . . . . . . . 8
3.2. Transit IPv6 Source TLV . . . . . . . . . . . . . . . . . 8
3.3. Transit IPv4 bidir TLV . . . . . . . . . . . . . . . . . . 9
3.4. Transit IPv6 bidir TLV . . . . . . . . . . . . . . . . . . 10
4. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5. IANA considerations . . . . . . . . . . . . . . . . . . . . . 11
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
7. Contributing authors . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
The mLDP specification [I-D.ietf-mpls-ldp-p2mp] describes mechanisms
for creating point-to-multipoint (P2MP) and multipoint-to-multipoint
MP2MP LSPs. These LSPs are typically used for transporting enduser
multicast packets. However, the mLDP specification does not provide
any rules for associating particular enduser multicast packets with
any particular LSP. Other drafts, like
[I-D.ietf-l3vpn-2547bis-mcast], describe applications in which out-
of-band signaling protocols, such as PIM and BGP, are used to
establish the mapping between an LSP and the multicast packets that
need to be forwarded over the LSP.
This draft describes an application in which the information needed
to establish the mapping between an LSP and the set of multicast
packets to be forwarded over it is carried in the "opaque value"
field of an mLDP FEC element. When an IP multicast tree (either a
source-specific tree or a bidirectional tree) enters the MPLS network
the (S,G) or (*,G) information from the IP multicast control plane
state is carried in the opaque value field of the mLDP FEC message.
As the tree leaves the MPLS network, this information is extracted
from the FEC element and used to build the IP multicast control
plane. PIM messages can be sent outside the MPLS domain. Note that
although the PIM control messages are sent periodically, the mLDP
messages are not.
Each IP multicast tree is mapped one-to-one to a P2MP or MP2MP 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 are known to be
limited in number.
1.1. Conventions used in this document
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].
1.2. Terminology
IP multicast tree : An IP multicast distribution tree identified by
an source IP address and/or IP multicast destination address, also
refered to as (S,G) and (*,G).
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RP: The PIM Rendezvous Point.
SSM: PIM Source Specific Multicast.
ASM: PIM Any Source Multicast.
mLDP : Multipoint LDP.
Transit LSP : An P2MP or MP2MP LSP whose FEC element contains the
(S,G) or (*,G) identifying a particular IP multicast distribution
tree.
In-band signaling : Using the opaque value of a mLDP FEC element to
carry the (S,G) or (*,G) indentifying a particular IP multicast
tree.
P2MP LSP: An LSP that has one Ingress LSR and one or more Egress
LSRs.
MP2MP LSP: An LSP that connects a set of leaf nodes, acting
indifferently as ingress or egress.
MP LSP: A multipoint LSP, either a P2MP or an MP2MP LSP.
Ingress LSR: Source of the P2MP LSP, also referred to as root node.
Egress LSR: One of potentially many destinations of an LSP, also
referred to as leaf node in the case of P2MP and MP2MP LSPs.
Transit LSR: An LSR that has one or more directly connected
downstream LSRs.
2. In-band signaling for MP LSPs
Suppose an LSR, call it D, is attached to a network that is capable
of MPLS multicast and IP multicast, and D is required to create a IP
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multicast tree due to a certain IP multicast event, like a PIM Join,
MSDP Source Announcement (SA) [RFC3618], BGP Source Active auto-
discovery route [I-D.rekhter-pim-sm-over-mldp] or Rendezvous Point
(RP) discovery. Suppose that D can determine that the IP multicast
tree needs to travel through the MPLS network until it reaches some
other LSR, U. For instance, when D looks up the route to the Source
or RP [RFC4601] of the IP multicast tree, it may discover that the
route is a BGP route with U as the BGP next hop. Then D may chose to
set up a P2MP or MP2MP LSP, with U as root, and to make that LSP
become part of the IP multicast distribution tree. Note that other
methods are possible to determine that an IP multicast tree is to be
transported across an MPLS network using P2MP or MP2MP LSPs, these
methods are outside the scope of this document.
Source or RP addresses that are reachable in a VPN context are
outside the scope of this document.
Multicast groups that operate in PIM Dense-Mode are outside the scope
of this document.
In order to establish a multicast tree via a P2MP or MP2MP LSP using
in-band signaling the source and the group will be encoded into an
mLDP opaque TLV encoding [I-D.ietf-mpls-ldp-p2mp]. The type of
encoding depends on the IP version. The tree type (P2MP or MP2MP)
depends on whether this is a source specific or a bidirectional
multicast tree. The root of the tree is the BGP next-hop that was
found during the route lookup on the source or RP. Using this
information a mLDP FEC is created and the LSP is build towards the
root of the LSP.
When an LSR receives a label mapping or withdraw and discovers it is
the root of the identified P2MP or MP2MP LSP, then the following
procedure is executed. If the opaque encoding of the FEC indicates
this is a Transit LSP (indicated by the opaque type), the opaque TLV
is decoded and the multicast source and group is passed to the
multicast code. If the multicast tree information is received via a
label mapping, the multicast code will add the downstream LDP
neighbor to the olist of the corresponding (S,G) or (*,G) state,
creating such state if it does not already exist. If it is due to a
label withdraw, the multicast code will remove the downstream LDP
neighbor from the olist of the corresponding (S,G) or (*,G) state.
From this point on normal PIM processing will occur.
2.1. Transiting Unidirectional IP multicast Shared Trees
Nothing prevents PIM shared trees, used by PIM-SM in the ASM service
model, from being transported across a MPLS core. However, it is not
possible to prune individual sources from the shared tree without the
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use of an additional out-of-band signaling protocol, like PIM or BGP
[I-D.rekhter-pim-sm-over-mldp]. For that reason transiting Shared
Trees across a Transit LSP is outside the scope of this draft.
2.2. Transiting IP multicast source trees
IP multicast source trees can either be created via PIM operating in
SSM mode [RFC4607] or ASM mode [RFC4601]. When PIM-SM is used in ASM
mode, the usual means of discovering active sources is to join a
sparse mode shared tree. However, this document does not provide any
method of establishing a sparse mode shared tree across an MPLS
network. To apply the technique of this document to PIM-SM in ASM
mode, there must be some other means of discovering the active
sources. One possible means is the use of MSDP [RFC3618]. Another
possible means is to use BGP Source Active auto-discovery routes, as
documented in [I-D.rekhter-pim-sm-over-mldp]. However, the method of
discovering the active sources is outside the scope of this document,
and as a result this document does not specify everything that is
needed to support the ASM service model using in-band signaling.
The source and group addresses are encoded into the a transit TLV as
specified in Section 3.1 and Section 3.2.
2.3. Transiting IP multicast bidirectional trees
Bidirectional IP multicast trees [RFC5015] MUST be transported across
a MPLS network using MP2MP LSPs. A bidirectional tree does not have
a specific source address; the group address, subnet mask and RP are
relevant for multicast forwarding. This document does not provide
procedures to discover RP to group mappings dynamically across an
MPLS network and assumes the RP is statically defined. Support of
dynamic RP mappings in combination with in-band signaling is outside
the scope of his document.
The RP for the group is used to select the ingress LSR and root of
the LSP. The group address is encoded according to the rules of
Section 3.3 or Section 3.4, depending on the IP version. The subnet
mask associated with the bidirectional group is encoded in the
Transit TLV. There are two types of bidirectional states in IP
multicast, the group specific state and the RP state. The first type
is typically created due to receiving a PIM join and has a subnet
mask of 32 for IPv4 and 128 for IPv6. The latter is typically
created via the static RP mapping and has a variable subnet mask.
The RP state is used to build a tree to the RP and used for sender
only branches. Each state (group specific and RP state) will result
in a separate MP2MP LSP. The merging of the two MP2MP LSPs will be
done by PIM on the root LSR. No speccial procedures are nessesary
for PIM to merge the two LSPs, each LSP is effectively treated as a
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PIM enabled interface. Please see [RFC5015] for more details.
For transporting the packets of a sender only branch we create a
MP2MP LSP. Other sender only branches will receive these packets and
will not forward them because there are no receivers. These packets
will be dropped. If that affect is undesireable some other means of
transport has to be established to forward packets to the root of the
tree, like a Multi-Point to Point LSP for example. A technique to
unicast packets to the root of a P2MP or MP2MP LSP is documented in
[I-D.rosen-l3vpn-mvpn-mspmsi] section 3.2.2.1 and
[I-D.ietf-mpls-ldp-p2mp] section 3.
3. LSP opaque encodings
This section documents the different transit opaque encodings.
3.1. Transit IPv4 Source 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 | Source
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 3 (to be assigned by IANA).
Length: 8 octets
Source: IPv4 multicast source address, 4 octets.
Group: IPv4 multicast group address, 4 octets.
3.2. Transit IPv6 Source TLV
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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 | Source ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Group ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 4 (to be assigned by IANA).
Length: 32 octets
Source: IPv6 multicast source address, 16 octets.
Group: IPv6 multicast group address, 16 octets.
3.3. Transit IPv4 bidir 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 | Mask Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 5 (to be assigned by IANA).
Length: 9 octets
Mask Len: The number of contiguous one bits that are left justified
and used as a mask, 1 octet.
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RP: Rendezvous Point (RP) IPv4 address used for encoded Group, 4
octets.
Group: IPv4 multicast group address, 4 octets.
3.4. Transit IPv6 bidir 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 | Mask Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 6 (to be assigned by IANA).
Length: 33 octets
Mask Len: The number of contiguous one bits that are left justified
and used as a mask, 1 octet.
RP: Rendezvous Point (RP) IPv6 address used for encoded group, 16
octets.
Group: IPv6 multicast group address, 16 octets.
4. Security Considerations
The same security considerations apply as for the base LDP
specification, as described in [RFC5036].
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5. IANA considerations
This document requires allocation from the 'LDP MP Opaque Value
Element basic type' name space managed by IANA. The values requested
are:
Transit IPv4 Source TLV type - 3
Transit IPv6 Source TLV type - 4
Transit IPv4 Bidir TLV type - 5
Transit IPv6 Bidir TLV type - 6
6. Acknowledgments
Thanks to Eric Rosen for his valuable comments on this draft. Also
thanks to Yakov Rekhter, Adrial Farrel, Uwe Joorde and Loa Andersson
for providing comments on this draft.
7. Contributing authors
Below is a list of the contributing authors in alphabetical order:
Toerless Eckert
Cisco Systems, Inc.
170 Tasman Drive
San Jose, CA, 95134
USA
E-mail: eckert@cisco.com
Nicolai Leymann
Deutsche Telekom
Winterfeldtstrasse 21
Berlin, 10781
Germany
E-mail: n.leymann@telekom.de
Maria Napierala
AT&T Labs
200 Laurel Avenue
Middletown, NJ 07748
USA
E-mail: mnapierala@att.com
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IJsbrand Wijnands
Cisco Systems, Inc.
De kleetlaan 6a
1831 Diegem
Belgium
E-mail: ice@cisco.com
8. References
8.1. Normative References
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[I-D.ietf-mpls-ldp-p2mp]
Minei, I., Kompella, K., Wijnands, I., and B. Thomas,
"Label Distribution Protocol Extensions for Point-to-
Multipoint and Multipoint-to-Multipoint Label Switched
Paths", draft-ietf-mpls-ldp-p2mp-11 (work in progress),
October 2010.
8.2. Informative References
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, August 2006.
[RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-
PIM)", RFC 5015, October 2007.
[RFC3618] Fenner, B. and D. Meyer, "Multicast Source Discovery
Protocol (MSDP)", RFC 3618, October 2003.
[I-D.ietf-l3vpn-2547bis-mcast]
Aggarwal, R., Bandi, S., Cai, Y., Morin, T., Rekhter, Y.,
Rosen, E., Wijnands, I., and S. Yasukawa, "Multicast in
MPLS/BGP IP VPNs", draft-ietf-l3vpn-2547bis-mcast-10 (work
in progress), January 2010.
[I-D.rekhter-pim-sm-over-mldp]
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Rekhter, Y., Aggarwal, R., and N. Leymann, "Carrying
PIM-SM in ASM mode Trees over P2MP mLDP LSPs",
draft-rekhter-pim-sm-over-mldp-02 (work in progress),
August 2010.
[I-D.rosen-l3vpn-mvpn-mspmsi]
Boers, A., Cai, Y., Napierala, M., Rosen, E., and I.
Wijnands, "MVPN: Optimized use of PIM via MS-PMSIs",
draft-rosen-l3vpn-mvpn-mspmsi-08 (work in progress),
January 2011.
Authors' Addresses
IJsbrand Wijnands (editor)
Cisco Systems, Inc.
De kleetlaan 6a
Diegem 1831
Belgium
Email: ice@cisco.com
Toerless Eckert
Cisco Systems, Inc.
170 Tasman Drive
San Jose CA, 95134
USA
Email: eckert@cisco.com
Nicolai Leymann
Deutsche Telekom
Winterfeldtstrasse 21
Berlin 10781
Germany
Email: n.leymann@telekom.de
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Maria Napierala
AT&T Labs
200 Laurel Avenue
Middletown NJ 07748
USA
Email: mnapierala@att.com
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