| Internet-Draft | MPTE Cap | July 2026 |
| Kompella | Expires 7 January 2027 | [Page] |
Multipath Traffic Engineering (MPTE) combines two approaches to traffic management: equal-cost multipath and constraint-based traffic engineering, offering a powerful new way to engineer networks. To avail of this, a node (possibly an ingress of a MPTE tunnel, or a path computation agent) must have information about the topology, link and node characteristics of a network so that it can compute the components of the MPTE tunnel. One important (node) characteristic is whether a given node supports MPTE, i.e., whether it can participate in the provisioning and maintenance of an MPTE tunnel.¶
Multicast TE (MCTE) offers a more efficient approach to traffic engineering for multicast traffic. Again, an important node characteristic is whether a given node supports MCTE, i.e., whether it can participate in the provisioning and maintenance of an MCTE tunnel.¶
This memo shows how these capabilities can be distributed in the IGP via Link State Routing TE Capabilities.¶
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[I-D.kompella-teas-mpte] introduces the notion of multipath traffic engineering (MPTE). It describes how an entity (MPTE DAG computer or MC) can compute a directed acyclic graph (DAG) from one or more ingress nodes to one or more egress nodes that meets given traffic engineering (TE) constraints. The MC (usually one of the ingresses, or a path computation engine) will need information about the network to do the computation, most of which is available in IGP TE extensions. Once the computation is done, the MC communicates the result to the signaling source (SS) which then signals (or provisions) the MPTE tunnel via one of the following protocols: RSVP-TE [RFC3209], PCEP [RFC5440] or BGP [RFC4271].¶
One key piece of information that is not currently in the IGP extensions is whether or not a given node supports MPTE, i.e., is capable of sending and receiving MPTE updates that create and maintain the tunnel. An MPTE tunnel cannot be setup through such a node, and thus the MC has to take this into account.¶
Similarly, [I-D.kompella-teas-mcte] proposes a new, more efficient approach to multicast traffic engineering (MCTE). There again, the MC would need to know if a given node can participate in an MCTE DAG.¶
This memo fills this gap.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. These words may also appear in this document in lower case as plain English words, absent their normative meanings.¶
This section provides definitions for terms and abbreviations that have a specific meaning to the MPTE protocol and that are used throughout this memo.¶
desired properties of paths between ingresses and egresses.¶
a directed graph that has no cycles.¶
a set of nodes and directed links. A network is represented by a directed graph.¶
an end node of an MPTE DAG.¶
a starting node of an MPTE DAG.¶
multicast TE with constraints that creates a multicast tree from an ingress to one or more egresses.¶
an MCTE DAG; the result of computation on MCTE constraints.¶
multipath TE with constraints that uses multiple paths from one or more ingresses to one or more egresses.¶
an MPTE DAG; the result of computation on MPTE constraints.¶
the entity computing the MCTED or MPTED, typically the ingress (if there is a single ingress) or a Path Computation Element¶
a vertex of a graph. A node may have associated attributes.¶
PCEP: Path Computation Element communication protocol.¶
[RFC5073] describes IGP protocol extension for the discovery of the TE capabilities of a node. This memo extends that with six new capabilities:¶
MCR bit: when set, this flag indicates that the node can process MCTE RSVP-TE messages.¶
MCP bit: when set, this flag indicates that the node can process MCTE PCEP messages.¶
MCB bit: when set, this flag indicates that the node can process MCTE BGP messages.¶
These bits are encoded in the TE Node Capability Descriptor defined in [RFC5073]. This Descriptor is carried in ISIS and OSPF as defined in the same RFC.¶
IANA is asked to allocate six bits for the above capabilities in the Link State Routing TE Capabilities registry.¶
This document specifies the content of the TE Node Capability Descriptor TLV in IS-IS and OSPF to be used for MPLS-TE path computation. As this TLV is not used for SPF computation or normal routing, the extensions specified here have no direct effect on IP routing. Tampering with this TLV may have an effect on Traffic Engineering computation. Mechanisms defined to secure IS-IS Link State PDUs [RFC3567], OSPF LSAs [RFC2154], and their TLVs can be used to secure this TLV as well.¶