Bidirectional Forwarding Detection (BFD) is a new protocol intended to detect faults in a data path between two forwarding engines, including physical interfaces, sub-interfaces (e.g., tunnel interfaces), data link(s), and to the extent possible the forwarding engines themselves, with potentially very low latency. An additional goal is to provide a single mechanism that can be used for liveliness detection over any media, at any protocol layer, with a wide range of detection times and overhead, to avoid a proliferation of different methods. These attributes of BFD makes it suitable for use by various MPLS applications. This presentation provides an overview of the BFD protocol and its use in MPLS networks.

One of the main uses of BFD in Operation and Maintenance (O&M) of MPLS networks. BFD can be used to complement LSP Ping for detecting MPLS data plane failures. Similarly, applications like Pseudo Wire (PW) Virtual Circuit Connection Verification (VCCV) can make use of BFD in the same context. Specifically, VCCV defines a set of messages that are exchanged between PEs to verify connectivity of the pseudowire (PW). In fault detection mode of VCCV, BFD can be used to detect liveliness of the PW. In the fault detection mode of PWE3, the upstream PE sends BFD control messages periodically. When the downstream PE doesn't receive BFD messages for a defined period of time, it declares that direction of the PW down and it notifies the upstream PE.

MPLS Traffic Engineering Fast Reroute (FRR) is another application which can benefit from BFD protocol. Specifically, MPLS FRR defines local protection schemes that provide fast recovery of protected TE LSPs upon link/SRLG/Node failure. One of the requirements of MPLS FRR is that failure detection should be performed in 10s of milliseconds. BFD protocol is designed to meet fast failure detection with 10s of milliseconds latency and hence is very suitable for failure detection at the link or node level for MPLS TE FRR. In this fashion, BFD can replace use of RSVP Hellos for MPLS FRR applications.

The other MPLS applications that can benefit from BFD's ability for liveliness detection over any media is maintenance of IGP adjacencies over PSC Forwarding Adjacency LSP (FA-LSP). Need for a failure detection mechanism for FA-LSP's arrives from the fact that IGP Hellos do not run and IGP adjacencies are not brought up for FA-LSPs. In current networks and implementations, RSVP Hellos are used as a mechanism for failure detection over FA-LSPs. With BFD providing a single mechanism that can be used for liveliness detection to avoid a proliferation of different methods, it makes perfect sense to replace RSVP Hellos with BFD for maintenance of IGP adjacencies over PSC FA-LSPs.

Use of BFD for MPLS application, especially for failure detection for MPLS PW, also poses very strict scalability requirements on the systems. This presentation also highlights these challenges and how they can be addressed by an implementation.

There has been tremendous interest from Service Providers for the use of BFD as a single mechanism that can be used for liveliness detection in IP and MPLS networks. It is due to this increasing interest that IETF Routing Area has establish a new working group chartered to specify BFD protocol and its usage for IP and MPLS networks. This presentation will also provide updates from BFD WG, with focus on the MPLS applications.

Speaker Bios:
Zafar Ali is a Technical Leader at Cisco Systems, Inc. where he leads software protocol development for MPLS/ GMPLS subsystem for Cisco Systems high speed, carrier-class routing business unit. Most recently Zafar has been focused on designing and developing GMPLS protocols and high availability solutions. Prior to joining Cisco, Zafar worked at Nortel Networks and Hughes Network Systems.

Zafar Ali received his Ph. D. and MS in Electrical and Computer Engineering from Purdue University, West Lafayette, Indiana. He obtained his Bachelor of Engineering in Electrical Engineering from NED University, where he was awarded the University Gold Medal.

Mallik Tatipamula is a Senior Product Manager at Cisco Systems, Inc. where he is responsible for Emerging technologies in Routing Technologies Group. Mallik has over 14 years of experience in telecom and networking. He closely works with service providers and national research networks around the world in deploying advanced technologies (IPv6, GMPLS) in their next generation networks.