Network Working Group I. Wijnands (Editor)
Internet-Draft T. Eckert
Intended status: Standards Track Cisco Systems, Inc.
Expires: April 27, 2010 N. Leymann
Deutsche Telekom
M. Napierala
AT&T Labs
October 24, 2009
mLDP based in-band signaling for Point-to-Multipoint and Multipoint-to-
Multipoint Label Switched Paths
draft-wijnands-mpls-mldp-in-band-signaling-02
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Abstract
When an IP multicast tree needs to pass through an MPLS domain, it is
advantageous to map the tree to a Point-to-Multipoint or Multipoint-
to-Multipoint Label Switched Path. This document specifies a way to
provide a one-one mapping between IP multicast trees and Label
Switched Paths using mLDP signaling. The IP multicast control
messages are translated into MPLS control messages when they enter
the MPLS domain, and are translated back into IP multicast control
messages at the far end of the MPLS domain. The IP multicast control
information is coded into the MPLS control information in such a way
as to ensure that a single Multipoint Label Switched Path gets set up
for each IP multicast tree.
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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 IP multicast source trees . . . . . . . . . . . 6
2.2. Transiting IP multicast bidirectional trees . . . . . . . 6
2.3. Transiting IP multicast shared Trees . . . . . . . . . . . 7
3. LSP opaque encodings . . . . . . . . . . . . . . . . . . . . . 7
3.1. Transit IPv4 Source TLV . . . . . . . . . . . . . . . . . 7
3.2. Transit IPv6 Source TLV . . . . . . . . . . . . . . . . . 8
3.3. Transit IPv4 bidir TLV . . . . . . . . . . . . . . . . . . 8
3.4. Transit IPv6 bidir TLV . . . . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5. IANA considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
7. Contributing authors . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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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
[I-D.ietf-mpls-ldp-p2mp] 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 IP multicast control messages used to set up the tree
are translated into mLDP messages. The (S,G) or (*,G) information
from the IP multicast control messages 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 messages that are sent outside the MPLS
domain. Note that although the IP multicast 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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mLDP : Multicast 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
signal multicast route information.
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 has the desire to create IP
multicast tree due to a certain IP multicast event, like a PIM Join,
MSDP Source Announcement (SA) [RFC3618] or 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 Rendezvous Point
(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
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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.
In order to send the multicast stream 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 stream. 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 will be executed. If the opaque encoding of the FEC
indicates this is an Transit LSP (indicated by the opaque type), the
opaque TLV will be decoded and the multicast source and group is
passed to the multicast code. If the multicast tree information was
received via a label mapping, the multicast code will effectively
treat this as a positif indication to create a IP multicast tree
based on the received information. If it was due to a label
withdraw, the multicast code will effectively treat this as having
received a negative indication and it will remove the tree
indentified by the encoded information. From this point on normal
PIM processing will occur.
2.1. Transiting IP multicast source trees
IP multicast source trees can either be created via PIM operating in
SSM mode [RFC4607] or ASM mode [RFC4601] (for example via last hop
behavior or MSDP [RFC3618]) and MUST be transporting across the MPLS
network using a P2MP LSP. A Transit LSP may be setup to forward the
IP multicast traffic across an MPLS core. If the multicast source is
reachable in a global table the source and group addresses are
encoded into the a transit TLV. Depending on the IP version it is
either Section 3.1 or Section 3.2.
2.2. 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; only the group address and subnet mask are
relevant for multicast forwarding. The RP for the group already
known by IP multicast is used to select the ingress PE and root of
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the LSP. The group address is encoded in either 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 bidirection states in IP multicast, the group
specific state and the RPA state. The first type is typlically
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 RP
mapping protocol and has a variable subnet mask. The RPA state is
used to build a tree to the RP and used for sender only branches.
Please see [RFC5015] for more details.
2.3. Transiting IP multicast shared Trees
Nothing prevents PIM shared trees from being transported across a
MPLS core. However, it is not possible to prune of individual
sources from the shared tree without the use of an additional out-of-
band signaling protocol, like PIM. For that reason transiting Shared
Trees across a Transit LSP is outside the scope of this draft.
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: 2 (to be assigned by IANA).
Length: 8
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Source: IPv4 multicast source address, 4 octets.
Group: IPv4 multicast group address, 4 octets.
3.2. Transit IPv6 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: 32
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 4 (to be assigned by IANA).
Length: 9
Mask Len: The number of contiguous one bits that are left justified
and used as a mask, 1 octet.
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: 4 (to be assigned by IANA).
Length: 33
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) 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].
5. IANA considerations
This document requires allocation from the LDP MP Opaque Value
Element type name space managed by IANA. The values requested are:
Transit IPv4 Source TLV type - requested 2
Transit IPv6 Source TLV type - requested 3
Transit IPv4 Bidir TLV type - requested 4
Transit IPv6 Bidir TLV type - requested 5
6. Acknowledgments
Thanks to Eric Rosen for his valuable comments on this draft. Also
thanks to Yakov Rekhter, Adrial Farrel and Uwe Joorde 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
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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
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., "Label Distribution Protocol Extensions for
Point-to-Multipoint and Multipoint-to-Multipoint Label
Switched Paths", draft-ietf-mpls-ldp-p2mp-05 (work in
progress), June 2008.
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.
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[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-07 (work
in progress), July 2008.
Authors' Addresses
IJsbrand Wijnands
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: nicolai.leymann@t-systems.com
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Maria Napierala
AT&T Labs
200 Laurel Avenue
Middletown NJ 07748
USA
Email: mnapierala@att.com
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