Bidirectional Forwarding Detection (BFD) for MPLS Label Switched Paths (LSPs)

Abstract

One desirable application of Bidirectional Forwarding Detection (BFD) is to detect a Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) data plane failure. LSP Ping is an existing mechanism for detecting MPLS data plane failures and for verifying the MPLS LSP data plane against the control plane. BFD can be used for the former, but not for the latter. However, the control plane processing required for BFD Control packets is relatively smaller than the processing required for LSP Ping messages. A combination of LSP Ping and BFD can be used to provide faster data plane failure detection and/or make it possible to provide such detection on a greater number of LSPs. This document describes the applicability of BFD in relation to LSP Ping for this application. It also describes procedures for using BFD in this environment.

Seamless Bidirectional Forwarding Detection (S-BFD) Use Cases

“…This comes at a cost: traffic is prevented from using the path/LSP until BFD is able to validate reachability; this could take seconds due to BFD session bring-up sequences [RFC5880], LSP Ping bootstrapping [RFC5884], etc. This use case would be better supported by eliminating the need for the initial BFD session negotiation.…”

“…BFD for multi-hop paths [RFC5883] and BFD for MPLS LSPs [RFC5884] perform end-to-end validation, traversing multiple network nodes. BFD has been designed to declare a failure to receive some number of consecutive packets.…”

“…BFD for MPLS LSPs, defined in [RFC5884], describes procedures for running BFD as an LSP in-band continuity check mechanism by using MPLS Echo Request messages [RFC4379] to bootstrap the BFD session on the target (i.e., egress) node. Section 4 of [RFC5884] also describes the possibility of running multiple BFD sessions per alternative of LSPs.…”

Configuration of Proactive Operations, Administration, and Maintenance (OAM) Functions for MPLS-Based Transport Networks Using Label Switched Path (LSP) Ping

“…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 Timer negotiation can be performed either in subsequent BFD control messages (in this case the operation is similar to bootstrapping based on LSP Ping described in [RFC5884]), or directly in the LSP Ping configuration messages.…”

“…Security of OAM protocols configured with extensions to LSP Ping described in this document are discussed in [RFC5880], [RFC5884], [RFC6374], [RFC6427], and [RFC6428].…”