Network Working Group I. Minei (Editor) Internet-Draft K. Kompella Intended status: Standards Track Juniper Networks Expires: April 27, 2010 I. Wijnands (Editor) B. Thomas Cisco Systems, Inc. October 24, 2009 Label Distribution Protocol Extensions for Point-to-Multipoint and Multipoint-to-Multipoint Label Switched Paths draft-ietf-mpls-ldp-p2mp-08 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 27, 2010. Copyright Notice Minei (Editor), et al. Expires April 27, 2010 [Page 1] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document describes extensions to the Label Distribution Protocol (LDP) for the setup of point to multi-point (P2MP) and multipoint-to- multipoint (MP2MP) Label Switched Paths (LSPs) in Multi-Protocol Label Switching (MPLS) networks. These extensions are also referred to as mLDP Multicast LDP. mLDP constructs the P2MP or MP2MP LSPs without interacting with or relying upon any other multicast tree construction protocol. Protocol elements and procedures for this solution are described for building such LSPs in a receiver-initiated manner. There can be various applications for P2MP/MP2MP LSPs, for example IP multicast or support for multicast in BGP/MPLS L3VPNs. Specification of how such applications can use a LDP signaled P2MP/ MP2MP LSP is outside the scope of this document. Minei (Editor), et al. Expires April 27, 2010 [Page 2] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1. Conventions used in this document . . . . . . . . . . . . 5 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 2. Setting up P2MP LSPs with LDP . . . . . . . . . . . . . . . . 6 2.1. Support for P2MP LSP setup with LDP . . . . . . . . . . . 7 2.2. The P2MP FEC Element . . . . . . . . . . . . . . . . . . . 7 2.3. The LDP MP Opaque Value Element . . . . . . . . . . . . . 9 2.3.1. The Generic LSP Identifier . . . . . . . . . . . . . . 9 2.4. Using the P2MP FEC Element . . . . . . . . . . . . . . . . 10 2.4.1. Label Map . . . . . . . . . . . . . . . . . . . . . . 11 2.4.2. Label Withdraw . . . . . . . . . . . . . . . . . . . . 12 2.4.3. Upstream LSR change . . . . . . . . . . . . . . . . . 13 3. Shared Trees . . . . . . . . . . . . . . . . . . . . . . . . . 13 4. Setting up MP2MP LSPs with LDP . . . . . . . . . . . . . . . . 14 4.1. Support for MP2MP LSP setup with LDP . . . . . . . . . . . 15 4.2. The MP2MP downstream and upstream FEC Elements. . . . . . 15 4.3. Using the MP2MP FEC Elements . . . . . . . . . . . . . . . 16 4.3.1. MP2MP Label Map . . . . . . . . . . . . . . . . . . . 17 4.3.2. MP2MP Label Withdraw . . . . . . . . . . . . . . . . . 20 4.3.3. MP2MP Upstream LSR change . . . . . . . . . . . . . . 21 5. Micro-loops in MP LSPs . . . . . . . . . . . . . . . . . . . . 21 6. The LDP MP Status TLV . . . . . . . . . . . . . . . . . . . . 22 6.1. The LDP MP Status Value Element . . . . . . . . . . . . . 23 6.2. LDP Messages containing LDP MP Status messages . . . . . . 23 6.2.1. LDP MP Status sent in LDP notification messages . . . 23 6.2.2. LDP MP Status TLV in Label Mapping Message . . . . . . 24 7. Upstream label allocation on a LAN . . . . . . . . . . . . . . 25 7.1. LDP Multipoint-to-Multipoint on a LAN . . . . . . . . . . 25 7.1.1. MP2MP downstream forwarding . . . . . . . . . . . . . 25 7.1.2. MP2MP upstream forwarding . . . . . . . . . . . . . . 25 8. Root node redundancy . . . . . . . . . . . . . . . . . . . . . 26 8.1. Root node redundancy - procedures for P2MP LSPs . . . . . 26 8.2. Root node redundancy - procedures for MP2MP LSPs . . . . . 27 9. Make Before Break (MBB) . . . . . . . . . . . . . . . . . . . 27 9.1. MBB overview . . . . . . . . . . . . . . . . . . . . . . . 28 9.2. The MBB Status code . . . . . . . . . . . . . . . . . . . 29 9.3. The MBB capability . . . . . . . . . . . . . . . . . . . . 29 9.4. The MBB procedures . . . . . . . . . . . . . . . . . . . . 30 9.4.1. Terminology . . . . . . . . . . . . . . . . . . . . . 30 9.4.2. Accepting elements . . . . . . . . . . . . . . . . . . 31 9.4.3. Procedures for upstream LSR change . . . . . . . . . . 31 9.4.4. Receiving a Label Map with MBB status code . . . . . . 32 9.4.5. Receiving a Notification with MBB status code . . . . 32 9.4.6. Node operation for MP2MP LSPs . . . . . . . . . . . . 32 10. Security Considerations . . . . . . . . . . . . . . . . . . . 33 11. IANA considerations . . . . . . . . . . . . . . . . . . . . . 33 Minei (Editor), et al. Expires April 27, 2010 [Page 3] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 34 13. Contributing authors . . . . . . . . . . . . . . . . . . . . . 34 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36 14.1. Normative References . . . . . . . . . . . . . . . . . . . 36 14.2. Informative References . . . . . . . . . . . . . . . . . . 36 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37 Minei (Editor), et al. Expires April 27, 2010 [Page 4] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 1. Introduction The LDP protocol is described in [RFC5036]. It defines mechanisms for setting up point-to-point (P2P) and multipoint-to-point (MP2P) LSPs in the network. This document describes extensions to LDP for setting up point-to-multipoint (P2MP) and multipoint-to-multipoint (MP2MP) LSPs. These are collectively referred to as multipoint LSPs (MP LSPs). A P2MP LSP allows traffic from a single root (or ingress) node to be delivered to a number of leaf (or egress) nodes. A MP2MP LSP allows traffic from multiple ingress nodes to be delivered to multiple egress nodes. Only a single copy of the packet will be sent on any link traversed by the MP LSP (see note at end of Section 2.4.1). This is accomplished without the use of a multicast protocol in the network. There can be several MP LSPs rooted at a given ingress node, each with its own identifier. The solution assumes that the leaf nodes of the MP LSP know the root node and identifier of the MP LSP to which they belong. The mechanisms for the distribution of this information are outside the scope of this document. The specification of how an application can use a MP LSP signaled by LDP is also outside the scope of this document. Interested readers may also wish to peruse the requirements draft [I-D.ietf-mpls-mp-ldp-reqs] and other documents [RFC4875] and [I-D.ietf-l3vpn-2547bis-mcast]. 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 The following terminology is taken from [I-D.ietf-mpls-mp-ldp-reqs]. P2P LSP: An LSP that has one Ingress LSR and one Egress LSR. P2MP LSP: An LSP that has one Ingress LSR and one or more Egress LSRs. MP2P LSP: An LSP that has one or more Ingress LSRs and one unique Egress LSR. Minei (Editor), et al. Expires April 27, 2010 [Page 5] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 MP2MP LSP: An LSP that connects a set of nodes, such that traffic sent by any node in the LSP is delivered to all others. MP LSP: A multipoint LSP, either a P2MP or an MP2MP LSP. Ingress LSR: An ingress LSR for a particular LSP is an LSR that can send a data packet along the LSP. MP2MP LSPs can have multiple ingress LSRs, P2MP LSPs have just one, and that node is often referred to as the "root node". Egress LSR: An egress LSR for a particular LSP is an LSR that can remove a data packet from that LSP for further processing. P2P and MP2P LSPs have only a single egress node, but P2MP and MP2MP LSPs can have multiple egress nodes. Transit LSR: An LSR that has reachability to the root of the MP LSP via a directly connected upstream LSR and one or more directly connected downstream LSRs. Bud LSR: An LSR that is an egress but also has one or more directly connected downstream LSRs. Leaf node: A Leaf node can be either an Egress or Bud LSR when referred in the context of a P2MP LSP. In the context of a MP2MP LSP, an LSR is both Ingress and Egress for the same MP2MP LSP and can also be a Bud LSR. 2. Setting up P2MP LSPs with LDP A P2MP LSP consists of a single root node, zero or more transit nodes and one or more leaf nodes. Leaf nodes initiate P2MP LSP setup and tear-down. Leaf nodes also install forwarding state to deliver the traffic received on a P2MP LSP to wherever it needs to go; how this is done is outside the scope of this document. Transit nodes install MPLS forwarding state and propagate the P2MP LSP setup (and tear- down) toward the root. The root node installs forwarding state to map traffic into the P2MP LSP; how the root node determines which traffic should go over the P2MP LSP is outside the scope of this document. Minei (Editor), et al. Expires April 27, 2010 [Page 6] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 2.1. Support for P2MP LSP setup with LDP Support for the setup of P2MP LSPs is advertised using LDP capabilities as defined in [I-D.ietf-mpls-ldp-capabilities]. An implementation supporting the P2MP procedures specified in this document MUST implement the procedures for Capability Parameters in Initialization Messages. A new Capability Parameter TLV is defined, the P2MP Capability. Following is the format of the P2MP Capability Parameter. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|0| P2MP Capability (TBD IANA) | Length (= 1) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1| Reserved | +-+-+-+-+-+-+-+-+ The P2MP Capability TLV MUST be supported in the LDP Initialization Message. Advertisement of the P2MP Capability indicates support of the procedures for P2MP LSP setup detailed in this document. If the peer has not advertised the corresponding capability, then no label messages using the P2MP FEC Element should be sent to the peer. 2.2. The P2MP FEC Element For the setup of a P2MP LSP with LDP, we define one new protocol entity, the P2MP FEC Element to be used as a FEC Element in the FEC TLV. Note that the P2MP FEC Element does not necessarily identify the traffic that must be mapped to the LSP, so from that point of view, the use of the term FEC is a misnomer. The description of the P2MP FEC Element follows. The P2MP FEC Element consists of the address of the root of the P2MP LSP and an opaque value. The opaque value consists of one or more LDP MP Opaque Value Elements. The opaque value is unique within the context of the root node. The combination of (Root Node Address, Opaque Value) uniquely identifies a P2MP LSP within the MPLS network. Minei (Editor), et al. Expires April 27, 2010 [Page 7] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 The P2MP FEC Element is encoded as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |P2MP Type (TBD)| Address Family | Address Length| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Root Node Address ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opaque Length | Opaque Value ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ~ ~ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: The type of the P2MP FEC Element is to be assigned by IANA. Address Family: Two octet quantity containing a value from ADDRESS FAMILY NUMBERS in [RFC3232] that encodes the address family for the Root LSR Address. Address Length: Length of the Root LSR Address in octets. Root Node Address: A host address encoded according to the Address Family field. Opaque Length: The length of the Opaque Value, in octets. Opaque Value: One or more MP Opaque Value elements, uniquely identifying the P2MP LSP in the context of the Root Node. This is described in the next section. If the Address Family is IPv4, the Address Length MUST be 4; if the Address Family is IPv6, the Address Length MUST be 16. No other Address Lengths are defined at present. If the Address Length doesn't match the defined length for the Address Family, the receiver SHOULD abort processing the message containing the FEC Element, and send an "Unknown FEC" Notification Minei (Editor), et al. Expires April 27, 2010 [Page 8] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 message to its LDP peer signaling an error. If a FEC TLV contains a P2MP FEC Element, the P2MP FEC Element MUST be the only FEC Element in the FEC TLV. 2.3. The LDP MP Opaque Value Element The LDP MP Opaque Value Element is used in the P2MP and MP2MP FEC Elements defined in subsequent sections. It carries information that is meaningful to Ingress LSRs and Leaf LSRs, but need not be interpreted by Transit LSRs. The LDP MP Opaque Value Element is encoded as follows: 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(TBD) | Length | Value ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ~ ~ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: The type of the LDP MP Opaque Value Element is to be assigned by IANA. Length: The length of the Value field, in octets. Value: String of Length octets, to be interpreted as specified by the Type field. 2.3.1. The Generic LSP Identifier The generic LSP identifier is a type of Opaque Value Element encoded as follows: Type: 1 (to be assigned by IANA) Minei (Editor), et al. Expires April 27, 2010 [Page 9] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 Length: 4 Value: A 32bit integer, unique in the context of the root, as identified by the root's address. This type of Opaque Value Element is recommended when mapping of traffic to LSPs is non-algorithmic, and done by means outside LDP. 2.4. Using the P2MP FEC Element This section defines the rules for the processing and propagation of the P2MP FEC Element. The following notation is used in the processing rules: 1. P2MP FEC Element : a FEC Element with Root Node Address X and Opaque Value Y. 2. P2MP Label Map : a Label Map message with a FEC TLV with a single P2MP FEC Element and Label TLV with label L. Label L MUST be allocated from the per-platform label space (see [RFC3031] section 3.14) of the LSR sending the Label Map Message. 3. P2MP Label Withdraw : a Label Withdraw message with a FEC TLV with a single P2MP FEC Element and Label TLV with label L. 4. P2MP LSP (or simply ): a P2MP LSP with Root Node Address X and Opaque Value Y. 5. The notation L' -> { ..., } on LSR X means that on receiving a packet with label L', X makes n copies of the packet. For copy i of the packet, X swaps L' with Li and sends it out over interface Ii. The procedures below are organized by the role which the node plays in the P2MP LSP. Node Z knows that it is a leaf node by a discovery process which is outside the scope of this document. During the course of protocol operation, the root node recognizes its role because it owns the Root Node Address. A transit node is any node (other than the root node) that receives a P2MP Label Map message (i.e., one that has leaf nodes downstream of it). Note that a transit node (and indeed the root node) may also be a leaf node. Minei (Editor), et al. Expires April 27, 2010 [Page 10] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 2.4.1. Label Map The remainder of this section specifies the procedures for originating P2MP Label Map messages and for processing received P2MP label map messages for a particular LSP. The procedures for a particular LSR depend upon the role that LSR plays in the LSP (ingress, transit, or egress). All labels discussed here are downstream-assigned [I-D.ietf-mpls-multicast-encaps] except those which are assigned using the procedures of Section 7. 2.4.1.1. Determining one's 'upstream LSR' Each node that is either an Leaf or Transit LSR of MP LSP needs to use the procedures below to select an upstream LSR. A node Z that wants to join a MP LSP determines the LDP peer U which is Z's next-hop on the best path from Z to the root node X. If there is more than one such LDP peer, only one of them is picked. U is Z's "Upstream LSR" for . When there are several candidate upstream LSRs, the LSR MAY select one upstream LSR using the following procedure: 1. The candidate upstream LSRs are numbered from lower to higher IP address 2. The following hash is performed: H = (Sum Opaque value) modulo N, where N is the number of candidate upstream LSRs 3. The selected upstream LSR U is the LSR that has the number H. This allows for load balancing of a set of LSPs among a set of candidate upstream LSRs, while ensuring that on a LAN interface a single upstream LSR is selected. 2.4.1.2. Determining the forwarding interface to an LSR Suppose LSR U receives a MP Label Map message from a downstream LSR D, specifying label L. Suppose further that U is connected to D over several LDP enabled interfaces or RSVP-TE Tunnel interfaces. If U needs to transmit to D a data packet whose top label is L, U is free to transmit the packet on any of those interfaces. LSR U is able to discover the directly connected interfaces via the LDP Discovery messages exchanged between the LSR U and D. The algorithm it uses to choose a particular interface for a particular such packet is a local matter. Minei (Editor), et al. Expires April 27, 2010 [Page 11] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 2.4.1.3. Leaf Operation A leaf node Z of P2MP LSP determines its upstream LSR U for as per Section 2.4.1.1, allocates a label L, and sends a P2MP Label Map to U. 2.4.1.4. Transit Node operation Suppose a transit node Z receives a P2MP Label Map from LSR T. Z checks whether it already has state for . If not, Z determines its upstream LSR U for as per Section 2.4.1.1. Using this Label Map to update the label forwarding table MUST NOT be done as long as LSR T is equal to LSR U. If LSR U is different from LSR T, Z will allocate a label L', and install state to swap L' with L over interface I associated with LSR T and send a P2MP Label Map to LSR U. Interface I is determind via the procedures in Section 2.4.1.2. If Z already has state for , then Z does not send a Label Map message for P2MP LSP . All that Z needs to do in this case is check that LSR T is not equal to the upstream LSR of and update its forwarding state. Assuming its old forwarding state was L'-> { ..., }, its new forwarding state becomes L'-> { ..., , }. If the LSR T is equal to the installed upstream LSR, the Label Map from LSR T MUST be retained and MUST not update the label forwarding table. 2.4.1.5. Root Node Operation Suppose the root node Z receives a P2MP Label Map from LSR T. Z checks whether it already has forwarding state for . If not, Z creates forwarding state to push label L onto the traffic that Z wants to forward over the P2MP LSP (how this traffic is determined is outside the scope of this document). If Z already has forwarding state for , then Z adds "push label L, send over interface I" to the nexthop, where I is the interface associated with LSR T and determind via the procedures in Section 2.4.1.2. 2.4.2. Label Withdraw The following lists procedures for generating and processing P2MP Label Withdraw messages for nodes that participate in a P2MP LSP. An LSR should apply those procedures that apply to it, based on its role in the P2MP LSP. Minei (Editor), et al. Expires April 27, 2010 [Page 12] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 2.4.2.1. Leaf Operation If a leaf node Z discovers (by means outside the scope of this document) that it has no downstream neighbors in that LSP, and that it has no need to be an egress LSR for that LSP, then it SHOULD send a Label Withdraw to its upstream LSR U for , where L is the label it had previously advertised to U for . 2.4.2.2. Transit Node Operation If a transit node Z receives a Label Withdraw message from a node W, it deletes label L from its forwarding state, and sends a Label Release message with label L to W. If deleting L from Z's forwarding state for P2MP LSP results in no state remaining for , then Z propagates the Label Withdraw for , to its upstream T, by sending a Label Withdraw where L1 is the label Z had previously advertised to T for . 2.4.2.3. Root Node Operation The procedure when the root node of a P2MP LSP receives a Label Withdraw message are the same as for transit nodes, except that it would not propagate the Label Withdraw upstream (as it has no upstream). 2.4.3. Upstream LSR change Suppose that for a given node Z participating in a P2MP LSP , the upstream LSR changes from U to U' as per Section 2.4.1.1. If U' is present in the forwarding table of then it MUST be removed. Z MUST also update its forwarding state by deleting the state for label L, allocating a new label, L', for , and installing the forwarding state for L'. Installing the forwarding state for L' MUST NOT be done before the forwarding state L is removed to avoid microloops. In addition Z MUST send a Label Map to U' and send a Label Withdraw to U. Note, if there was a downstream mapping from U that was not installed in the forwarding due to Section 2.4.1.4 it can now be installed. 3. Shared Trees The mechanism described above shows how to build a tree with a single root and multiple leaves, i.e., a P2MP LSP. One can use essentially the same mechanism to build Shared Trees with LDP. A Shared Tree can be used by a group of routers that want to multicast traffic among Minei (Editor), et al. Expires April 27, 2010 [Page 13] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 themselves, i.e., each node is both a root node (when it sources traffic) and a leaf node (when any other member of the group sources traffic). A Shared Tree offers similar functionality to a MP2MP LSP, but the underlying multicasting mechanism uses a P2MP LSP. One example where a Shared Tree is useful is video-conferencing. Another is Virtual Private LAN Service (VPLS) [RFC4664], where for some types of traffic, each device participating in a VPLS must send packets to every other device in that VPLS. One way to build a Shared Tree is to build an LDP P2MP LSP rooted at a common point, the Shared Root (SR), and whose leaves are all the members of the group. Each member of the Shared Tree unicasts traffic to the SR (using, for example, the MP2P LSP created by the unicast LDP FEC advertised by the SR); the SR then splices this traffic into the LDP P2MP LSP. The SR may be (but need not be) a member of the multicast group. A major advantage of this approach is that no further protocol mechanisms beyond the one already described are needed to set up a Shared Tree. Furthermore, a Shared Tree is very efficient in terms of the multicast state in the network, and is reasonably efficient in terms of the bandwidth required to send traffic. A property of this approach is that a sender will receive its own packets as part of the multicast; thus a sender must be prepared to recognize and discard packets that it itself has sent. For a number of applications (for example, VPLS), this requirement is easy to meet. Another consideration is the various techniques that can be used to splice unicast LDP MP2P LSPs to the LDP P2MP LSP; these will be described in a later revision. 4. Setting up MP2MP LSPs with LDP An MP2MP LSP is much like a P2MP LSP in that it consists of a single root node, zero or more transit nodes and one or more leaf LSRs acting equally as Ingress or Egress LSR. A leaf node participates in the setup of an MP2MP LSP by establishing both a downstream LSP, which is much like a P2MP LSP from the root, and an upstream LSP which is used to send traffic toward the root and other leaf nodes. Transit nodes support the setup by propagating the upstream and downstream LSP setup toward the root and installing the necessary MPLS forwarding state. The transmission of packets from the root node of a MP2MP LSP to the receivers is identical to that for a P2MP LSP. Traffic from a downstream node follows the upstream LSP toward the root node and branches downward along the downstream LSP as required to reach other leaf nodes. A packet that is received from a downstream node MUST never be forwarded back out to that same node. Minei (Editor), et al. Expires April 27, 2010 [Page 14] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 Mapping traffic to the MP2MP LSP may happen at any leaf node. How that mapping is established is outside the scope of this document. Due to how a MP2MP LSP is built a leaf LSR that is sending packets on the MP2MP LSP does not receive its own packets. There is also no additional mechanism needed on the root or transit LSR to match upstream traffic to the downstream forwarding state. Packets that are forwarded over a MP2MP LSP will not traverse a link more than once, with the possible exception of LAN links (see Section 4.3.1), if the procedures of [I-D.ietf-mpls-upstream-label] are not provided. 4.1. Support for MP2MP LSP setup with LDP Support for the setup of MP2MP LSPs is advertised using LDP capabilities as defined in [I-D.ietf-mpls-ldp-capabilities]. An implementation supporting the MP2MP procedures specified in this document MUST implement the procedures for Capability Parameters in Initialization Messages. A new Capability Parameter TLV is defined, the MP2MP Capability. Following is the format of the MP2MP Capability Parameter. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|0| MP2MP Capability (TBD IANA) | Length (= 1) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1| Reserved | +-+-+-+-+-+-+-+-+ The MP2MP Capability TLV MUST be supported in the LDP Initialization Message. Advertisement of the MP2MP Capability indicates support of the procedures for MP2MP LSP setup detailed in this document. If the peer has not advertised the corresponding capability, then no label messages using the MP2MP upstream and downstream FEC Elements should be sent to the peer. 4.2. The MP2MP downstream and upstream FEC Elements. For the setup of a MP2MP LSP with LDP we define 2 new protocol entities, the MP2MP downstream FEC and upstream FEC Element. Both elements will be used as FEC Elements in the FEC TLV. Note that the MP2MP FEC Elements do not necessarily identify the traffic that must be mapped to the LSP, so from that point of view, the use of the term FEC is a misnomer. The description of the MP2MP FEC Elements follow. The structure, encoding and error handling for the MP2MP downstream and upstream FEC Elements are the same as for the P2MP FEC Element Minei (Editor), et al. Expires April 27, 2010 [Page 15] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 described in Section 2.2. The difference is that two new FEC types are used: MP2MP downstream type (TBD) and MP2MP upstream type (TBD). If a FEC TLV contains an MP2MP FEC Element, the MP2MP FEC Element MUST be the only FEC Element in the FEC TLV. Note, except when using the procedures of [I-D.ietf-mpls-upstream-label], the MPLS labels used are "downstream- assigned" [I-D.ietf-mpls-multicast-encaps], even if they are bound to the "upstream FEC element". 4.3. Using the MP2MP FEC Elements This section defines the rules for the processing and propagation of the MP2MP FEC Elements. The following notation is used in the processing rules: 1. MP2MP downstream LSP (or simply downstream ): an MP2MP LSP downstream path with root node address X and opaque value Y. 2. MP2MP upstream LSP (or simply upstream ): a MP2MP LSP upstream path for downstream node D with root node address X and opaque value Y. 3. MP2MP downstream FEC Element : a FEC Element with root node address X and opaque value Y used for a downstream MP2MP LSP. 4. MP2MP upstream FEC Element : a FEC Element with root node address X and opaque value Y used for an upstream MP2MP LSP. 5. MP2MP-D Label Map : A Label Map message with a FEC TLV with a single MP2MP downstream FEC Element and label TLV with label L. Label L MUST be allocated from the per-platform label space (see [RFC3031] section 3.14) of the LSR sending the Label Map Message. 6. MP2MP-U Label Map : A Label Map message with a FEC TLV with a single MP2MP upstream FEC Element and label TLV with label Lu. Label L MUST be allocated from the per-platform label space (see [RFC3031] section 3.14) of the LSR sending the Label Map Message. Minei (Editor), et al. Expires April 27, 2010 [Page 16] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 7. MP2MP-D Label Withdraw : a Label Withdraw message with a FEC TLV with a single MP2MP downstream FEC Element and label TLV with label L. 8. MP2MP-U Label Withdraw : a Label Withdraw message with a FEC TLV with a single MP2MP upstream FEC Element and label TLV with label Lu. 9. MP2MP-D Label Release : a Label Release message with a FEC TLV with a single MP2MP downstream FEC Element and label TLV with label L. 10. MP2MP-U Label Release : a Label Release message with a FEC TLV with a single MP2MP upstream FEC Element and label TLV with label Lu. The procedures below are organized by the role which the node plays in the MP2MP LSP. Node Z knows that it is a leaf node by a discovery process which is outside the scope of this document. During the course of the protocol operation, the root node recognizes its role because it owns the root node address. A transit node is any node (other then the root node) that receives a MP2MP Label Map message (i.e., one that has leaf nodes downstream of it). Note that a transit node (and indeed the root node) may also be a leaf node and the root node does not have to be an ingress LSR or leaf of the MP2MP LSP. 4.3.1. MP2MP Label Map The remainder of this section specifies the procedures for originating MP2MP Label Map messages and for processing received MP2MP label map messages for a particular LSP. The procedures for a particular LSR depend upon the role that LSR plays in the LSP (ingress, transit, or egress). All labels discussed here are downstream-assigned [I-D.ietf-mpls-multicast-encaps] except those which are assigned using the procedures of Section 7. 4.3.1.1. Determining one's upstream MP2MP LSR Determining the upstream LDP peer U for a MP2MP LSP follows the procedure for a P2MP LSP described in Section 2.4.1.1. Minei (Editor), et al. Expires April 27, 2010 [Page 17] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 4.3.1.2. Determining one's downstream MP2MP LSR A LDP peer U which receives a MP2MP-D Label Map from a LDP peer D will treat D as downstream MP2MP LSR. 4.3.1.3. Installing the upstream path of a MP2MP LSP There are two methods for installing the upstream path of a MP2MP LSP to a downstream neighbor. 1. We can install the upstream MP2MP path (to a downstream neighbor) based on receiving a MP2MP-D Label Map from the downstream neighbor. This will install the upstream path on a per hop by hop bases. 2. We install the upstream MP2MP path (to a downstream neighbor) based on receiving a MP2MP-U Label Map from the upstream neighbor. An LSR does not need to wait for the MP2MP-U Label Map if it is the root of the MP2MP LSP or already has received an MP2MP-U Label Map from the upstream neighbor. We call this method ordered mode. The typical result of this mode is that the downstream path of the MP2MP is build hop by hop towards the root. Once the root is reached, the root node will trigger a MP2MP-U Label Map to the downstream neighbor(s). For setting up the upstream path of a MP2MP LSP ordered mode MUST be used. Due to ordered mode the upstream path of the MP2MP LSP is installed at the leaf node once the path to the root is completed. The advantage is that when a leaf starts sending immediately after the upstream path is installed, packets are able to reach the root node without being dropped due to an incomplete LSP. Method 1 is not able to guarantee that the upstream path is completed before the leaf starts sending. 4.3.1.4. MP2MP leaf node operation A leaf node Z of a MP2MP LSP determines its upstream LSR U for as per Section 4.3.1.1, allocates a label L, and sends a MP2MP-D Label Map to U. Leaf node Z expects an MP2MP-U Label Map from node U in response to the MP2MP-D Label Map it sent to node U. Z checks whether it already has forwarding state for upstream . If not, Z creates forwarding state to push label Lu onto the traffic that Z wants to forward over the MP2MP LSP. How it determines what traffic to forward on this MP2MP LSP is outside the scope of this document. Minei (Editor), et al. Expires April 27, 2010 [Page 18] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 4.3.1.5. MP2MP transit node operation Suppose node Z receives a MP2MP-D Label Map from LSR D. Z checks whether it has forwarding state for downstream . If not, Z determines its upstream LSR U for as per Section 4.3.1.1. Using this Label Map to update the label forwarding table MUST NOT be done as long as LSR D is equal to LSR U. If LSR U is different from LSR D, Z will allocate a label L' and install downstream forwarding state to swap label L' with label L over interface I associated with LSR D and send a MP2MP-D Label Map to U. Interface I is determind via the procedures in Section 2.4.1.2. If Z already has forwarding state for downstream , all that Z needs to do in this case is check that LSR D is not equal to the upstream LSR of and update its forwarding state. Assuming its old forwarding state was L'-> { ..., }, its new forwarding state becomes L'-> { ..., , }. If the LSR D is equal to the installed upstream LSR, the Label Map from LSR D MUST be retained and MUST not update the label forwarding table. Node Z checks if upstream LSR U already assigned a label Lu to . If not, transit node Z waits until it receives a MP2MP-U Label Map from LSR U. See Section 4.3.1.3. Once the MP2MP-U Label Map is received from LSR U, node Z checks whether it already has forwarding state upstream . If it does, then no further action needs to happen. If it does not, it allocates a label Lu' and creates a new label swap for Lu' with Label Lu over interface Iu. Interface Iu is determind via the procedures in Section 2.4.1.2. In addition, it also adds the label swap(s) from the forwarding state downstream , omitting the swap on interface I for node D. The swap on interface I for node D is omitted to prevent packet originated by D to be forwarded back to D. Node Z determines the downstream MP2MP LSR as per Section 4.3.1.2, and sends a MP2MP-U Label Map to node D. 4.3.1.6. MP2MP root node operation 4.3.1.6.1. Root node is also a leaf Suppose root/leaf node Z receives a MP2MP-D Label Map from node D. Z checks whether it already has forwarding state downstream . If not, Z creates forwarding state for downstream to push label L on traffic that Z wants to forward down the MP2MP LSP. How it determines what traffic to forward on this MP2MP LSP is outside the scope of this document. If Z already has forwarding state for Minei (Editor), et al. Expires April 27, 2010 [Page 19] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 downstream , then Z will add the label push for L over interface I to it. Interface I is determind via the procedures in Section 2.4.1.2. Node Z checks if it has forwarding state for upstream If not, Z allocates a label Lu' and creates upstream forwarding state to push Lu' with the label push(s) from the forwarding state downstream , except the push on interface I for node D. This allows upstream traffic to go down the MP2MP to other node(s), except the node from which the traffic was received. Node Z determines the downstream MP2MP LSR as per section Section 4.3.1.2, and sends a MP2MP-U Label Map to node D. Since Z is the root of the tree Z will not send a MP2MP-D Label Map and will not receive a MP2MP-U Label Map. 4.3.1.6.2. Root node is not a leaf Suppose the root node Z receives a MP2MP-D Label Map from node D. Z checks whether it already has forwarding state for downstream . If not, Z creates downstream forwarding state and installs a outgoing label L over interface I. Interface I is determind via the procedures in Section 2.4.1.2. If Z already has forwarding state for downstream , then Z will add label L over interface I to the existing state. Node Z checks if it has forwarding state for upstream . If not, Z allocates a label Lu' and creates forwarding state to swap Lu' with the label swap(s) from the forwarding state downstream , except the swap for node D. This allows upstream traffic to go down the MP2MP to other node(s), except the node is was received from. Root node Z determines the downstream MP2MP LSR D as per Section 4.3.1.2, and sends a MP2MP-U Label Map to it. Since Z is the root of the tree Z will not send a MP2MP-D Label Map and will not receive a MP2MP-U Label Map. 4.3.2. MP2MP Label Withdraw The following lists procedures for generating and processing MP2MP Label Withdraw messages for nodes that participate in a MP2MP LSP. An LSR should apply those procedures that apply to it, based on its role in the MP2MP LSP. 4.3.2.1. MP2MP leaf operation If a leaf node Z discovers (by means outside the scope of this document) that it has no downstream neighbors in that LSP, and that it has no need to be an egress LSR for that LSP, then it SHOULD send a MP2MP-D Label Withdraw to its upstream LSR U for , Minei (Editor), et al. Expires April 27, 2010 [Page 20] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 where L is the label it had previously advertised to U for . Leaf node Z will also send a unsolicited label release to U to indicate that the upstream path is no longer used and that Label Lu can be removed. Leaf node Z expects the upstream router U to respond by sending a downstream label release for L. 4.3.2.2. MP2MP transit node operation If a transit node Z receives a MP2MP-D Label Withdraw message from node D, it deletes label L from its forwarding state downstream and from all its upstream states for . Node Z sends a MP2MP-D Label Release message with label L to D. Since node D is no longer part of the downstream forwarding state, Z cleans up the forwarding state upstream . There is no need to send an MP2MP-U Label Withdraw to D because node D already removed Lu and send a label release for Lu to Z. If deleting L from Z's forwarding state for downstream results in no state remaining for , then Z propagates the MP2MP-D Label Withdraw to its upstream node U for and will also send a unsolicited MP2MP-U Label Release to U to indicate that the upstream path is no longer used and that Label Lu can be removed. 4.3.2.3. MP2MP root node operation The procedure when the root node of a MP2MP LSP receives a MP2MP-D Label Withdraw message is the same as for transit nodes, except that the root node would not propagate the Label Withdraw upstream (as it has no upstream). 4.3.3. MP2MP Upstream LSR change The procedure for changing the upstream LSR is the same as documented in Section 2.4.3, except it is applied to MP2MP FECs, using the procedures described in Section 4.3.1 through Section 4.3.2.3. 5. Micro-loops in MP LSPs Micro-loops created by the unicast routing protocol during convergence may also effect mLDP MP LSPs. Since the tree building logic in mLDP is based on unicast routing, a unicast routing loop may also result in a micro-loop in the MP LSPs. Micro-loops that involve 2 directly connected routers don't create a loop in mLDP. mLDP is able to prevent this inconsistency by never allowing an upstream LDP Minei (Editor), et al. Expires April 27, 2010 [Page 21] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 neighbor to be added as a downstream LDP neighbor into the LFT for the same FEC. Micro-loops that involve more then 2 LSRs are not prevented. Micro-loops that involve more then 2 LSRs may create a micro-loop in the downstream path of either a MP2MP LSP or P2MP LSP and the upstream path of the MP2MP LSP. The loops are transient and will disappear as soon as the unicast routing protocol converges. Micro- loops that occur in the upstream path of a MP2MP LSP may be detected by including LDP path vector in the MP2MP-U Label Map messages. These procedures are currently under investigation and are subjected to further study. 6. The LDP MP Status TLV An LDP MP capable router MAY use an LDP MP Status TLV to indicate additional status for a MP LSP to its remote peers. This includes signaling to peers that are either upstream or downstream of the LDP MP capable router. The value of the LDP MP status TLV will remain opaque to LDP and MAY encode one or more status elements. The LDP MP Status TLV is encoded as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|0| LDP MP Status Type(TBD) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Value | ~ ~ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LDP MP Status Type: The LDP MP Status Type to be assigned by IANA. Length: Length of the LDP MP Status Value in octets. Value: One or more LDP MP Status Value elements. Minei (Editor), et al. Expires April 27, 2010 [Page 22] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 6.1. The LDP MP Status Value Element The LDP MP Status Value Element that is included in the LDP MP Status TLV Value has the following encoding. 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(TBD) | Length | Value ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ~ ~ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: The type of the LDP MP Status Value Element is to be assigned by IANA. Length: The length of the Value field, in octets. Value: String of Length octets, to be interpreted as specified by the Type field. 6.2. LDP Messages containing LDP MP Status messages The LDP MP status message may appear either in a label mapping message or a LDP notification message. 6.2.1. LDP MP Status sent in LDP notification messages An LDP MP status TLV sent in a notification message must be accompanied with a Status TLV. The general format of the Notification Message with an LDP MP status TLV is: Minei (Editor), et al. Expires April 27, 2010 [Page 23] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0| Notification (0x0001) | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Status TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LDP MP Status TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Optional LDP MP FEC TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Optional Label TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Status TLV status code is used to indicate that LDP MP status TLV and an additional information follows in the Notification message's "optional parameter" section. Depending on the actual contents of the LDP MP status TLV, an LDP P2MP or MP2MP FEC TLV and Label TLV may also be present to provide context to the LDP MP Status TLV. (NOTE: Status Code is pending IANA assignment). Since the notification does not refer to any particular message, the Message Id and Message Type fields are set to 0. 6.2.2. LDP MP Status TLV in Label Mapping Message An example of the Label Mapping Message defined in RFC3036 is shown below to illustrate the message with an Optional LDP MP Status TLV present. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0| Label Mapping (0x0400) | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | FEC TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Optional LDP MP Status TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Additional Optional Parameters | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Minei (Editor), et al. Expires April 27, 2010 [Page 24] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 7. Upstream label allocation on a LAN On a LAN, the procedures so far discussed would require the upstream LSR to send a copy of the packet to each receiver individually. If there is more then one receiver on the LAN we don't take full benefit of the multi-access capability of the network. We may optimize the bandwidth consumption on the LAN and replication overhead on the upstream LSR by using upstream label allocation [I-D.ietf-mpls-upstream-label]. Procedures on how to distribute upstream labels using LDP is documented in [I-D.ietf-mpls-ldp-upstream]. 7.1. LDP Multipoint-to-Multipoint on a LAN The procedure to allocate a context label on a LAN is defined in [I-D.ietf-mpls-upstream-label]. That procedure results in each LSR on a given LAN having a context label which, on that LAN, can be used to identify itself uniquely. Each LSR advertises its context label as an upstream-assigned label, following the procedures of [I-D.ietf-mpls-ldp-upstream]. Any LSR for which the LAN is a downstream link on some P2MP or MP2MP LSP will allocate an upstream- assigned label identifying that LSP. When the LSR forwards a packet downstream on one of those LSPs, the packet's top label must be the LSR's context label, and the packet's second label is the label identifying the LSP. We will call the top label the "upstream LSR label" and the second label the "LSP label". 7.1.1. MP2MP downstream forwarding The downstream path of a MP2MP LSP is much like a normal P2MP LSP, so we will use the same procedures as defined in [I-D.ietf-mpls-ldp-upstream]. A label request for a LSP label is send to the upstream LSR. The label mapping that is received from the upstream LSR contains the LSP label for the MP2MP FEC and the upstream LSR context label. The MP2MP downstream path (corresponding to the LSP label) will be installed the context specific forwarding table corresponding to the upstream LSR label. Packets sent by the upstream router can be forwarded downstream using this forwarding state based on a two label lookup. 7.1.2. MP2MP upstream forwarding A MP2MP LSP also has an upstream forwarding path. Upstream packets need to be forwarded in the direction of the root and downstream on any node on the LAN that has a downstream interface for the LSP. For a given MP2MP LSP on a given LAN, exactly one LSR is considered to be the upstream LSR. If an LSR on the LAN receives a packet from one of its downstream interfaces for the LSP, and if it needs to forward the Minei (Editor), et al. Expires April 27, 2010 [Page 25] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 packet onto the LAN, it ensures that the packet's top label is the context label of the upstream LSR, and that its second label is the LSP label that was assigned by the upstream LSR. Other LSRs receiving the packet will not be able to tell whether the packet really came from the upstream router, but that makes no difference in the processing of the packet. The upstream LSR will see its own upstream LSR in the label, and this will enable it to determine that the packet is traveling upstream. 8. Root node redundancy The root node is a single point of failure for an MP LSP, whether this is P2MP or MP2MP. The problem is particularly severe for MP2MP LSPs. In the case of MP2MP LSPs, all leaf nodes must use the same root node to set up the MP2MP LSP, because otherwise the traffic sourced by some leafs is not received by others. Because the root node is the single point of failure for an MP LSP, we need a fast and efficient mechanism to recover from a root node failure. An MP LSP is uniquely identified in the network by the opaque value and the root node address. It is likely that the root node for an MP LSP is defined statically. The root node address may be configured on each leaf statically or learned using a dynamic protocol. How leafs learn about the root node is out of the scope of this document. Suppose that for the same opaque value we define two (or more) root node addresses and we build a tree to each root using the same opaque value. Effectively these will be treated as different MP LSPs in the network. Once the trees are built, the procedures differ for P2MP and MP2MP LSPs. The different procedures are explained in the sections below. 8.1. Root node redundancy - procedures for P2MP LSPs Since all leafs have set up P2MP LSPs to all the roots, they are prepared to receive packets on either one of these LSPs. However, only one of the roots should be forwarding traffic at any given time, for the following reasons: 1) to achieve bandwidth savings in the network and 2) to ensure that the receiving leafs don't receive duplicate packets (since one cannot assume that the receiving leafs are able to discard duplicates). How the roots determine which one is the active sender is outside the scope of this document. Minei (Editor), et al. Expires April 27, 2010 [Page 26] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 8.2. Root node redundancy - procedures for MP2MP LSPs Since all leafs have set up an MP2MP LSP to each one of the root nodes for this opaque value, a sending leaf may pick either of the two (or more) MP2MP LSPs to forward a packet on. The leaf nodes receive the packet on one of the MP2MP LSPs. The client of the MP2MP LSP does not care on which MP2MP LSP the packet is received, as long as they are for the same opaque value. The sending leaf MUST only forward a packet on one MP2MP LSP at a given point in time. The receiving leafs are unable to discard duplicate packets because they accept on all LSPs. Using all the available MP2MP LSPs we can implement redundancy using the following procedures. A sending leaf selects a single root node out of the available roots for a given opaque value. A good strategy MAY be to look at the unicast routing table and select a root that is closest in terms of the unicast metric. As soon as the root address of the active root disappears from the unicast routing table (or becomes less attractive) due to root node or link failure, the leaf can select a new best root address and start forwarding to it directly. If multiple root nodes have the same unicast metric, the highest root node addresses MAY be selected, or per session load balancing MAY be done over the root nodes. All leafs participating in a MP2MP LSP MUST join to all the available root nodes for a given opaque value. Since the sending leaf may pick any MP2MP LSP, it must be prepared to receive on it. The advantage of pre-building multiple MP2MP LSPs for a single opaque value is that convergence from a root node failure happens as fast as the unicast routing protocol is able to notify. There is no need for an additional protocol to advertise to the leaf nodes which root node is the active root. The root selection is a local leaf policy that does not need to be coordinated with other leafs. The disadvantage of pre-building multiple MP2MP LSPs is that more label resources are used, depending on how many root nodes are defined. 9. Make Before Break (MBB) An LSR selects as its upstream LSR for a MP LSP the LSR that is its next hop to the root of the LSP. When the best path to reach the root changes the LSR must choose a new upstream LSR. Sections Section 2.4.3 and Section 4.3.3 describe these procedures. When the best path to the root changes the LSP may be broken temporarily resulting in packet loss until the LSP "reconverges" to a new upstream LSR. The goal of MBB when this happens is to keep the Minei (Editor), et al. Expires April 27, 2010 [Page 27] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 duration of packet loss as short as possible. In addition, there are scenarios where the best path from the LSR to the root changes but the LSP continues to forward packets to the prevous next hop to the root. That may occur when a link comes up or routing metrics change. In such a case a new LSP should be established before the old LSP is removed to limit the duration of packet loss. The procedures described below deal with both scenarios in a way that an LSR does not need to know which of the events described above caused its upstream router for an MBB LSP to change. This MBB procedures are an optional extension to the MP LSP building procedures described in this draft. 9.1. MBB overview The MBB procedues use additional LDP signaling. Suppose some event causes a downstream LSR-D to select a new upstream LSR-U for FEC-A. The new LSR-U may already be forwarding packets for FEC-A; that is, to downstream LSR's other than LSR-D. After LSR-U receives a label for FEC-A from LSR-D, it will notify LSR-D when it knows that the LSP for FEC-A has been established from the root to itself. When LSR-D receives this MBB notification it will change its next hop for the LSP root to LSR-U. The assumption is that if LSR-U has received an MBB notification from its upstream router for the FEC-A LSP and has installed forwarding state the LSP it is capable of forwarding packets on the LSP. At that point LSR-U should signal LSR-D by means of an MBB notification that it has become part of the tree identified by FEC-A and that LSR-D should initiate its switchover to the LSP. At LSR-U the LSP for FEC-A may be in 1 of 3 states. 1. There is no state for FEC-A. 2. State for FEC-A exists and LSR-U is waiting for MBB notification that the LSP from the root to it exists. 3. State for FEC-A exists and the MBB notification has been received. After LSR-U receives LSR-D's Label Mapping message for FEC-A LSR-U MUST NOT reply with an MBB notification to LSR-D until its state for the LSP is state #3 above. If the state of the LSP at LSR-U is state #1 or #2, LSR-U should remember receipt of the Label Mapping message from LSR-D while waiting for an MBB notification from its upstream LSR for the LSP. When LSR-U receives the MBB notification from its Minei (Editor), et al. Expires April 27, 2010 [Page 28] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 upstream LSR it transitions to LSP state #3 and sends an MBB notification to LSR-D. 9.2. The MBB Status code As noted in Section 9.1, the procedures to establish an MBB MP LSP are different from those to establish normal MP LSPs. When a downstream LSR sends a Label Mapping message for MP LSP to its upstream LSR it MAY include an LDP MP Status TLV that carries a MBB Status Code to indicate MBB procedures apply to the LSP. This new MBB Status Code MAY also appear in an LDP Notification message used by an upstream LSR to signal LSP state #3 to the downstream LSR; that is, that the upstream LSR's state for the LSP exists and that it has received notification from its upstream LSR that the LSP is in state #3. The MBB Status is a type of the LDP MP Status Value Element as described in Section 6.1. It is encoded as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBB Type = 1 | Length = 1 | Status code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ MBB Type: Type 1 (to be assigned by IANA) Length: 1 Status code: 1 = MBB request 2 = MBB ack 9.3. The MBB capability An LSR MAY advertise that it is capable of handling MBB LSPs using the capability advertisement as defined in [I-D.ietf-mpls-ldp-capabilities]. The LDP MP MBB capability has the following format: Minei (Editor), et al. Expires April 27, 2010 [Page 29] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|0| LDP MP MBB Capability | Length = 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1| Reserved | +-+-+-+-+-+-+-+-+ Note: LDP MP MBB Capability (Pending IANA assignment) 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|0| LDP MP MBB Capability | Length = 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1| Reserved | +-+-+-+-+-+-+-+-+ If an LSR has not advertised that it is MBB capable, its LDP peers MUST NOT send it messages which include MBB parameters. If an LSR receives a Label Mapping message with a MBB parameter from downstream LSR-D and its upstream LSR-U has not advertised that it is MBB capable, the LSR MUST send an MBB notification immediatly to LSR-U (see Section 9.4). If this happens an MBB MP LSP will not be established, but normal a MP LSP will be the result. 9.4. The MBB procedures 9.4.1. Terminology 1. MBB LSP : A P2MP or MP2MP Make Before Break (MBB) LSP entry with Root Node Address X and Opaque Value Y. 2. A(N, L): An Accepting element that consists of an upstream Neighbor N and Local label L. This LSR assigned label L to neighbor N for a specific MBB LSP. For an active element the corresponding Label is stored in the label forwarding database. 3. iA(N, L): An inactive Accepting element that consists of an upstream neighbor N and local Label L. This LSR assigned label L to neighbor N for a specific MBB LSP. For an inactive element the corresponding Label is not stored in the label forwarding database. Minei (Editor), et al. Expires April 27, 2010 [Page 30] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 4. F(N, L): A Forwarding state that consists of downstream Neighbor N and Label L. This LSR is sending label packets with label L to neighbor N for a specific FEC. 5. F'(N, L): A Forwarding state that has been marked for sending a MBB Notification message to Neighbor N with Label L. 6. MBB Notification : A LDP notification message with a MP LSP , Label L and MBB Status code 2. 7. MBB Label Map : A P2MP Label Map or MP2MP Label Map downstream with a FEC element , Label L and MBB Status code 1. 9.4.2. Accepting elements An accepting element represents a specific label value L that has been advertised to a neighbor N for a MBB LSP and is a candidate for accepting labels switched packets on. An LSR can have two accepting elements for a specific MBB LSP LSP, only one of them MUST be active. An active element is the element for which the label value has been installed in the label forwarding database. An inactive accepting element is created after a new upstream LSR is chosen and is pending to replace the active element in the label forwarding database. Inactive elements only exist temporarily while switching to a new upstream LSR. Once the switch has been completed only one active element remains. During network convergence it is possible that an inactive accepting element is created while an other inactive accepting element is pending. If that happens the older inactive accepting element MUST be replaced with an newer inactive element. If an accepting element is removed a Label Withdraw has to be send for label L to neighbor N for . 9.4.3. Procedures for upstream LSR change Suppose a node Z has a MBB LSP with an active accepting element A(N1, L1). Due to a routing change it detects a new best path for root X and selects a new upstream LSR N2. Node Z allocates a new local label L2 and creates an inactive accepting element iA(N2, L2). Node Z sends MBB Label Map to N2 and waits for the new upstream LSR N2 to respond with a MBB Notification for . During this transition phase there are two accepting elements, the element A(N1, L1) still accepting packets from N1 over label L1 and the new inactive element iA(N2, L2). While waiting for the MBB Notification from upstream LSR N2, it is possible that an other transition occurs due to a routing change. Suppose the new upstream LSR is N3. An inactive element iA(N3, L3) Minei (Editor), et al. Expires April 27, 2010 [Page 31] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 is created and the old inactive element iA(N2, L2) MUST be removed. A label withdraw MUST be sent to N2 for from N2 will be ignored because the inactive element is removed. It is possible that the MBB Notification from upstream LSR is never received due to link or node failure. To prevent waiting indefinitely for the MBB Notification a timeout SHOULD be applied. As soon as the timer expires, the procedures in Section 9.4.5 are applied as if a MBB Notification was received for the inactive element. 9.4.4. Receiving a Label Map with MBB status code Suppose node Z has state for a MBB LSP and receives a MBB Label Map from N2. A new forwarding state F(N2, L2) will be added to the MP LSP if it did not already exist. If this MBB LSP has an active accepting element or node Z is the root of the MBB LSP a MBB notification is send to node N2. If node Z has an inactive accepting element it marks the Forwarding state as . 9.4.5. Receiving a Notification with MBB status code Suppose node Z receives a MBB Notification from N. If node Z has state for MBB LSP and an inactive accepting element iA(N, L) that matches with N and L, we activate this accepting element and install label L in the label forwarding database. If an other active accepting was present it will be removed from the label forwarding database. If this MBB LSP also has Forwarding states marked for sending MBB Notifications, like , MBB Notifications are send to these downstream LSRs. If node Z receives a MBB Notification for an accepting element that is not inactive or does not match the Label value and Neighbor address, the MBB notification is ignored. 9.4.6. Node operation for MP2MP LSPs The procedures described above apply to the downstream path of a MP2MP LSP. The upstream path of the MP2MP is setup as normal without including a MBB Status code. If the MBB procedures apply to a MP2MP downstream FEC element, the upstream path to a node N is only installed in the label forwarding database if node N is part of the active accepting element. If node N is part of an inactive accepting element, the upstream path is installed when this inactive accepting element is activated. Minei (Editor), et al. Expires April 27, 2010 [Page 32] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 10. Security Considerations The same security considerations apply as for the base LDP specification, as described in [RFC5036]. 11. IANA considerations This document creates a new name space (the LDP MP Opaque Value Element type) that is to be managed by IANA, and the allocation of the value 1 for the type of Generic LSP Identifier. This document requires allocation of three new LDP FEC Element types: 1. the P2MP FEC type - requested value 0x06 2. the MP2MP-up FEC type - requested value 0x07 3. the MP2MP-down FEC type - requested value 0x08 This document requires the assignment of three new code points for three new Capability Parameter TLVs, corresponding to the advertisement of the P2MP, MP2MP and MBB capabilities. The values requested are: P2MP Capability Parameter - requested value 0x0508 MP2MP Capability Parameter - requested value 0x0509 MBB Capability Parameter - requested value 0x050A This document requires the assignment of a LDP Status Code to indicate a LDP MP Status TLV is following in the Notification message. The value requested from the LDP Status Code Name Space: LDP MP status - requested value 0x00000040 This document requires the assigment of a new code point for a LDP MP Status TLV. The value requested from the LDP TLV Type Name Space: LDP MP Status TLV Type - requested value 0x096F This document creates a new name space (the LDP MP Status Value Element type) that is to be managed by IANA, and the allocation of the value 1 for the type of MBB Status. Minei (Editor), et al. Expires April 27, 2010 [Page 33] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 12. Acknowledgments The authors would like to thank the following individuals for their review and contribution: Nischal Sheth, Yakov Rekhter, Rahul Aggarwal, Arjen Boers, Eric Rosen, Nidhi Bhaskar, Toerless Eckert, George Swallow, Jin Lizhong, Vanson Lim, Adrian Farrel and Thomas Morin. 13. Contributing authors Below is a list of the contributing authors in alphabetical order: Shane Amante Level 3 Communications, LLC 1025 Eldorado Blvd Broomfield, CO 80021 US Email: Shane.Amante@Level3.com Luyuan Fang Cisco Systems 300 Beaver Brook Road Boxborough, MA 01719 US Email: lufang@cisco.com Hitoshi Fukuda NTT Communications Corporation 1-1-6, Uchisaiwai-cho, Chiyoda-ku Tokyo 100-8019, Japan Email: hitoshi.fukuda@ntt.com Yuji Kamite NTT Communications Corporation Tokyo Opera City Tower 3-20-2 Nishi Shinjuku, Shinjuku-ku, Tokyo 163-1421, Japan Email: y.kamite@ntt.com Minei (Editor), et al. Expires April 27, 2010 [Page 34] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 Kireeti Kompella Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 US Email: kireeti@juniper.net Ina Minei Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 US Email: ina@juniper.net Jean-Louis Le Roux France Telecom 2, avenue Pierre-Marzin Lannion, Cedex 22307 France Email: jeanlouis.leroux@francetelecom.com Bob Thomas Cisco Systems, Inc. 300 Beaver Brook Road Boxborough, MA, 01719 E-mail: bobthomas@alum.mit.edu Lei Wang Telenor Snaroyveien 30 Fornebu 1331 Norway Email: lei.wang@telenor.com IJsbrand Wijnands Cisco Systems, Inc. De kleetlaan 6a 1831 Diegem Belgium E-mail: ice@cisco.com 14. References Minei (Editor), et al. Expires April 27, 2010 [Page 35] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 14.1. 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. [RFC3232] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an On-line Database", RFC 3232, January 2002. [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, January 2001. [I-D.ietf-mpls-upstream-label] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream Label Assignment and Context-Specific Label Space", draft-ietf-mpls-upstream-label-05 (work in progress), April 2008. [I-D.ietf-mpls-ldp-upstream] Aggarwal, R. and J. Roux, "MPLS Upstream Label Assignment for LDP", draft-ietf-mpls-ldp-upstream-02 (work in progress), November 2007. [I-D.ietf-mpls-ldp-capabilities] Thomas, B., "LDP Capabilities", draft-ietf-mpls-ldp-capabilities-02 (work in progress), March 2008. 14.2. Informative References [RFC4664] Andersson, L. and E. Rosen, "Framework for Layer 2 Virtual Private Networks (L2VPNs)", RFC 4664, September 2006. [RFC4875] Aggarwal, R., Papadimitriou, D., and S. Yasukawa, "Extensions to Resource Reservation Protocol - Traffic Engineering (RSVP-TE) for Point-to-Multipoint TE Label Switched Paths (LSPs)", RFC 4875, May 2007. [I-D.ietf-mpls-mp-ldp-reqs] Roux, J., "Requirements for Point-To-Multipoint Extensions to the Label Distribution Protocol", draft-ietf-mpls-mp-ldp-reqs-04 (work in progress), February 2008. [I-D.ietf-l3vpn-2547bis-mcast] Aggarwal, R., Bandi, S., Cai, Y., Morin, T., Rekhter, Y., Minei (Editor), et al. Expires April 27, 2010 [Page 36] Internet-Draft P2MP and MP2MP LSP Setup with LDP October 2009 Rosen, E., Wijnands, I., and S. Yasukawa, "Multicast in MPLS/BGP IP VPNs", draft-ietf-l3vpn-2547bis-mcast-06 (work in progress), January 2008. [I-D.ietf-mpls-multicast-encaps] Eckert, T., Rosen, E., Aggarwal, R., and Y. Rekhter, "MPLS Multicast Encapsulations", draft-ietf-mpls-multicast-encaps-09 (work in progress), May 2008. Authors' Addresses Ina Minei Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 US Email: ina@juniper.net Kireeti Kompella Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 US Email: kireeti@juniper.net IJsbrand Wijnands Cisco Systems, Inc. De kleetlaan 6a Diegem 1831 Belgium Email: ice@cisco.com Bob Thomas Cisco Systems, Inc. 300 Beaver Brook Road Boxborough 01719 US Email: bobthomas@alum.mit.edu Minei (Editor), et al. Expires April 27, 2010 [Page 37]