P2MP Policy Ping

Each P2MP Policy can have multiple Candidate Paths (CPs). The CP with highest preference is designated as the active CP, while all other CPs are the backup CPs. To enable seamless global optimization a CP MAY consist of multiple Path Instances (PIs), allowing for Make-Before-Break (MBB) procedures between an active PI and a newly established, optimized PI. A PI is the actual P2MP tunnel set up from the root to a set of leaves via transit routers. A PI is identified on the Root node by the rootID which is the Root's node IP address, treeID and PI's instance ID. To ensure reliable network operation, it is essential to verify end-to-end connectivity for both active and backup CPs, as well as all associated PIs. This document specifies a mechanism for detecting data plane failures within a P2MP Policy CP and its associated PIs, enabling operators to monitor and troubleshoot multicast path integrity. This specification applies exclusively to Replication Segments (Replication SIDs) that use MPLS encapsulation for forwarding and does not cover Segment Routing over IPv6 (SRv6). The mechanisms described herein build upon the concepts established in for P2MP MPLS Operations, Administration, and Maintenance (OAM). All consideration and limitations described in section 6 of applies to this document as well.

section 1.1 defines terms specific to SR Replication Segment and also explains the Node terminology in a Multicast domain, including the Root Node, Leaf Node and a Bud Node. section 2, defines terms and concepts specific to SR P2MP Policy including the CP and the PI.

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 when, and only when, they appear in all capitals, as shown here.

A P2MP Policy and its corresponding Replication Segments are typically provisioned via a centralized controller or configured statically using YANG models or CLI. The root and the leaves are discovered in accordance with and the multicast tree is computed from the root to the leaves. However, there is no underlay signaling protocol to distribute the P2MP Policy from the root to the leaf routers. Consequently, when a P2MP tree fails to deliver user traffic, identifying the failure can be challenging without ping and traceroute mechanisms to isolate faults along the tree. To address this challenge, P2MP Policy ping and traceroute can be utilized to detect and localize faults within the P2MP tree and its associated Replication Segments, as defined in . These OAM tools enable periodic ping operations to verify connectivity between the root and the leaves. In cases where a ping fails, a traceroute can be initiated to determine the point of failure along the tree. This diagnostic process can be initiated from the node responsible for establishing the P2MP Policy, ensuring proactive monitoring and rapid fault detection.

Ping/Traceroute packets are forwarded on the P2MP Policy, on a specific CP and its PIs toward the designated leaf routers. These packets are replicated at the replication point based on the Replication Segment forwarding information on the corresponding router. This document specifically addresses Replication Segments that use MPLS encapsulation. Future documents will extend support for Replication Segments using SRv6 encapsulation. Packets are processed based on the standard behavior when their Time-to-Live (TTL) expires or when they reach the egress (leaf) router. The appropriate respond is sent back to the root node following the procedures outlined in .

The procedures in define fault detection and isolation mechanisms for P2MP MPLS LSPs. These mechanisms extend the LSP ping techniques described in such that they may be applied to P2MP MPLS LSPs, ensuring alignment with existing fault management tools. emphasizes the reuse of existing LSP ping mechanisms designed for Point-to-Point P2P LSPs, adapting them to P2MP MPLS LSPs to facilitate seamless implementation and network operation. The fault detection procedures specified in are applicable to all P2MP MPLS protocols, including P2MP RSVP-TE and Multicast LDP and now P2MP SR Policy. While highlights specific differences for P2MP RSVP-TE and Multicast LDP, this document introduces considerations unique to P2MP SR Policies, including: Egress Address P2MP Responder Sub-TLVs: Multicast LDP, as per section 3.2.1 of , does not allow for the inclusion of Egress Address P2MP Responder Sub-TLVs, as upstream LSRs lack visibility into downstream leaf nodes. Similarly, P2MP SR Policies often rely on a Path Computation Element (PCE) for programming transit routers, meaning these routers do not have knowledge of the leaf nodes. Only the Root node, where the P2MP SR Policy is programmed, may have visibility into the leaf nodes. Consequently, these Sub-TLVs SHOULD NOT be used when an echo request carries a P2MP Policy MPLS Candidate Path FEC. End of Processing for Traceroutes: In Multicast LDP LSPs, the initiating LSR may not always be aware of all egress nodes, unlike P2MP RSVP-TE. In the case of P2MP SR Policies, the Root of the tree may have full visibility into the egress nodes if the P2MP SR Policy is PCC-initiated. If the P2MP SR Policy is PCE-initiated, the Root may or may not have visibility into the egress nodes, as this depends on the specific implementation and configuration of the PCE. Based on this, a P2MP SR Policy SHOULD follow the recommendations in Section 4.3.1 of , depending on the level of visibility the Root has into the egress nodes. For example, in a PCC-initiated P2MP SR Policy, the Root can learn egress node identities through Next-Generation MVPN procedures and BGP, as described in . In contrast, for a PCE-initiated P2MP SR Policy, the PCE may not provide the egress node information to the Root, making this process optional and implementation-specific. Identification of the LSP under test: , in Section 3.1, defines distinct identifiers for P2MP RSVP-TE and Multicast LDP when identifying an LSP under test. As each protocol has its own identifier, this document introduces a new Target FEC Stack TLV specific to P2MP SR Policies to uniquely identify their Candidate Paths (CPs) and Path Instances (PIs). These modifications ensure that P2MP Policy OAM mechanisms are properly aligned with existing MPLS ping and traceroute tools while addressing the specific operational characteristics of P2MP SR Policies.

In addition to major differences outlined in the previous section, P2MP SR Policies SHOULD adhere to the common procedures specified in for P2MP MPLS LSPs. Furthermore, this specification reuses the same destination UDP port as defined in for consistency with existing MPLS OAM mechanism. Implementations MUST account for the fact that a P2MP Policy may contain multiple CPs, and each CP may consist of multiple PIs. As such, implementations SHOULD support the ability to individually test each CP and its corresponding PI using Ping and Traceroute mechanisms. The Ping and Traceroute packets MUST be forwarded along the specified CP and its PI, traversing the associated Replication Segments. When a downstream node receives a Ping or Traceroute packet, it MUST process the request and generate a response even if the CP and its PI are not currently the active path.

In certain deployments, two Replication Segments may be interconnected via an intermediate Unicast SR domain. In such scenarios, proper TTL handling is required based on the hierarchical MPLS TTL mode being used (e.g., Pipe Mode vs. Uniform Mode). For example, when a P2MP Policy Ping or Traceroute packet enters an Unicast SR domain, it MUST be processed on the two interconnecting Replication Segments, based on the Replication SID and its TTL value. The SR domain itself SHOULD be treated as a single hop, meaning that the Replication SID TTL MUST be decremented by one before pushing the Unicast SR SIDs onto the Replication SID stack. Failure detection within the SR domain itself is considered out of scope for this document.

The packet format used in this specification follow section 3 of . However, additional TLVs and sub-TLVs are required to support the new functionality introduced for P2MP Policies. These extensions are described in the following sections.

defines a standardized mechanism for detecting data-plane failures in Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs). To correctly identify the Replication Segment associated with a given Candidate Path (CP) and Path Instance (PI), the Echo Request message MUST include a Target FEC Stack TLV that explicitly specifies the Candidate Path and Path Instance under test. This document introduces a new sub-TLV, referred to as the P2MP Policy MPLS Candidate Path sub-TLV, which is defined as follows:

Further details regarding the structure and processing of this sub-TLV are provided in subsequent sections.

The P2MP Policy MPLS Candidate Path sub-TLV value field follows the format specified in Section 2 of . The structure of this sub-TLV is illustrated in the figure below.

Address Family: (2 octets) containing a value from ADDRESS FAMILY NUMBERS in , indicating the address family of the Root Address. Address Length: (1 octets) specifying the length of the Root Address in octets (4 octets for IPv4, 16 octets for IPv6). Root: (variable length depending on the address family field) The root node of the P2MP Policy, as defined in Tree-ID: (4 octets) A unique identifier for the P2MP tree, as defined in Instance-ID: (2 octets) identifies the specific Path-Instance as defined in

As specified in section 3.2 of , four sub-TLVs are used within the P2MP Responder Identifier TLV included in the echo request message. The Sub-TLVs for IPv4 and IPv6 egress addresses of P2MP responder are aligned with section 3.2.1 of . The sub-TLVs for IPv4 and IPv6 node addresses of the P2MP responder are aligned with Section 3.2.2 of These mechanisms ensure that responses are appropriately scoped to limit unnecessary processing and improve the efficiency of P2MP OAM procedures.

Note to the RFC Editor: please remove this section before publication. This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in RFC7942 . The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist. According to RFC7942, "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit".

Nokia has implemented and . In addition, Nokia has implemented P2MP policy ping as defined in this draft to verify the end to end connectivity of a P2MP tree in segment routing domain. The implementation supports SR-MPLS encapsulation and has all the MUST and SHOULD clause in this draft. The implementation is at general availability maturity and is compliant with the latest version of the draft. The documentation for implementation can be found at Nokia help and the point of contact is hooman.bidgoli@nokia.com.

IANA has assigned the following code points TEMPORARY for sub-type values to the following sub-TLVs under TLV type 1 (Target FEC Stack) from the "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters" registry, "TLVs and sub-TLVs" sub-registry. This sub-type value is assigned from the standards Action of range 0-16383 for TLV type 1 (Target FEC Stack) 41: P2MP Policy MPLS Candidate Path

Overall, the security needs for P2MP policy ping is same as . The P2MP policy ping is susceptible to the same three attack vectors as explained in RFC8029 section 5. The same procedures and recommendations explained in section 5 should be taken and implemented to mitigate these attack vectors for P2MP policy Ping as well.