Definition of P2MP PW TLV for Label Switched Path (LSP) Ping Mechanisms
Extracted elements (11)
An Aggregate P2MP Tree requires an upstream-assigned label so that on the Leaf PE (L-PE), traffic can be associated with a VPN or VPLS instance, because many P2MP PWs can share the same P2MP MPLS LSP. For an Inclusive P2MP Tree, the P2MP MPLS LSP label itself uniquely identifies the service being carried.
For Inclusive and Selective P2MP Trees, the echo request is sent using only the P2MP MPLS LSP label. For Aggregate Inclusive and Aggregate Selective P2MP Trees, a label stack of [P2MP MPLS LSP label (outer), upstream assigned P2MP PW label (inner)] is required because multiple VPN/VPLS instances share the same P2MP MPLS LSP and the upstream-assigned label disambiguates the service instance.
L-PEs use the GAL and IPv4/IPv6 ACH Channel header, or PW ACH, to determine that an arriving packet is an OAM packet. L-PEs process the P2MP Pseudowire sub-TLV in the Target FEC Stack TLV per Section 4.4 of RFC 8029 and respond according to the processing rules in that document.
The procedures from RFC 6425 for preventing congestion of Echo Responses (Echo Jitter TLV, Section 3.3 of RFC 6425) and limiting echo replies to a single L-PE (Node Address P2MP Responder Identifier TLV, Section 3.2 of RFC 6425) should be applied to P2MP PW LSP Ping.
Implementations of this document MUST support both OAM ping encapsulation options: GAL followed by an IPv4 or IPv6 ACH, and PW ACH.
For an Inclusive P2MP Tree, the echo request is sent with either {P2MP LSP label, GAL} and IPv4/IPv6 ACH, or {P2MP LSP label} and PW ACH. For an Aggregate Inclusive Tree, the echo request uses {P2MP LSP label, P2MP PW upstream assigned label, GAL} and IPv4/IPv6 ACH, or {P2MP LSP label, P2MP PW upstream assigned label} and PW ACH.
This document defines a new P2MP Pseudowire sub-TLV for the Target Forwarding Equivalence Class (FEC) Stack TLV used in LSP Ping. It is added by the Root PE (R-PE) originator of the echo request to identify the P2MP PW under test at the Leaf PE (L-PE).
Two encapsulation options are defined for the LSP Ping echo request over P2MP PW: (1) GAL [RFC6426] followed by an IPv4 (0x0021) or IPv6 (0x0057) type Associated Channel Header (ACH), and (2) PW ACH [RFC4385].
IANA assigned sub-TLV type value 37 ('P2MP Pseudowire') from the 'Sub-TLVs for TLV Types 1, 16, and 21' sub-registry within the 'Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters' registry.
This document does not introduce any new security considerations beyond those that already apply to RFC 6425, which specifies LSP Ping extensions for detecting data-plane failures in P2MP MPLS.
The P2MP Pseudowire sub-TLV contains: AGI Type (1 octet), AGI Length (1 octet), AGI Value (variable), IP Addr Len (1 octet), and Originating Router's IP Addr (variable, IPv4 or IPv6 as determined by IP Addr Len). The AGI identifies the VPLS instance; the Originating Router's IP is the address of the P2MP PW root.