Q&A: What is BFD? What is the Silverline standpoint on BFD?


  • What is BFD ?
  • What is the Silverline standpoint on BFD ?



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What is BFD?

Bidirectional Forwarding Detection (BFD) is a network protocol used to detect faults between two forwarding engines connected by a link. It provides low-overhead detection of faults even on physical media that doesn't support failure detection of any kind, such as Ethernet, virtual circuits, tunnels and MPLS Label Switched Paths.

BFD establishes a session between two endpoints over a particular link. If more than one link exists between two systems, multiple BFD sessions may be established to monitor each one of them. The session is established with a three-way handshake, and is torn down the same way. Authentication may be enabled on the session. A choice of simple password, MD5 or SHA1 authentication is available.

BFD does not have a discovery mechanism; sessions must be explicitly configured between endpoints. BFD may be used on many different underlying transport mechanisms and layers, and operates independently of all of these. Therefore, it needs to be encapsulated by whatever transport it uses. For example, monitoring MPLS LSPs involves piggybacking session establishment on LSP-Ping packets. Protocols that support some form of adjacency setup, such as OSPF or IS-IS, may also be used to bootstrap a BFD session. These protocols may then use BFD to receive faster notification of failing links than would normally be possible using the protocol's own keepalive mechanism.

What is the Silverline standpoint on BFD ?

Silverline doesn't allow the use of BFD. We have found in our testing that BFD, while well adapted to the datacenter, proves to be counter-productive across higher latency links such as GRE tunnels that traverse the Internet. In other words, the BGP session stability over GRE tunnels decreases when using BFD versus using the built-in BGP hold timers.


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