Working Group, We had very active discussion (yay!) at the microphone as part of Mahesh's presentation on BFD Performance Measurement. (draft-am-bfd-performance)
I wanted to start this thread to discuss the greater underlying issues this discussion raised. In particular, active tuning of BFD session parameters. Please note that opinions I state here are as an individual contributor. BFD clients typically want the fastest, most stable detection interval that is appropriate to their application. That stability component is very important since too aggressive of timers can result in unnecessary BFD session instability which will impact the subscribing application. Such stability is a function of many things, scale of the system running BFD being a major one. In my opinion, applications should generally choose a detection interval that is reasoanble for their application rather than try to dynamically discover the lowest possible stable detection interval. This is because a number of unstable factors, such as CPU load, contention with other network traffic and other things that are outside the general control of many sytems may impact such scale. That said, here's a few thoughts on active feedback mechanisms: 1. BFD is asymmetric. This means a receiving BFD implementation must provide feedback to a sending implementation in order for it to understand perceived reliability. 2. Measurement infrastructure may negatively impact session scale. Greg, I believe, made this point when discussing host processing issues vs. BFD ingress/egress. 3. Detection interval calculations really need to take into account things that are greater than simple packet transmission times. As an example, if your measurement is always taken during low system CPU or network activity, how high is your confidence about the interval? What about scaling vs. number of total BFD sessions? I have no strong conclusions here, just some cautionary thoughts. What are yours? -- Jeff
