Exam 300-420 topic 1 question 62 discussion

The BFD feature that uses less CPU usage is BFD asynchronous mode.

This question of kind of tricky. BFD has echo mode and echo disable mode (aynchronous mode). echo mode waits for bfd packets from opposite router and the session goes down. On the other hand, the session goes down without bfd packet from the opposite router on echo disable mode. But i am not sure if changing from echo mode to asynchronous mode lowers cpu usage. so i guess i will go with the answer A

The BFD feature that uses less CPU usage is BFD asynchronous mode. In asynchronous mode, BFD sessions are initiated independently by each router in a BFD adjacency. This means that each router sends BFD packets periodically, regardless of whether or not it has received any BFD packets from its neighbor. In contrast, BFD synchronous mode requires both routers in a BFD adjacency to agree on the interval at which BFD packets are sent. This means that both routers must be synchronized, which can require more CPU resources. Additionally, BFD asynchronous mode does not require BFD packets to be acknowledged. This means that BFD packets can be sent and received more quickly, which can also reduce CPU usage.

A y B son las dos válidas. Pero con A aumentas el tiempo de convergencia y con B estás cambiando el modo de funcionamiento del BFD. No te especifica qué es lo que puedes cambiar. Pues a saber.

The correct answer is B. Implement BFD asynchronous mode between peers with low CPU resources. Bidirectional Forwarding Detection (BFD) has two modes of operation: echo mode and asynchronous mode. In echo mode, BFD packets are sent back and forth between peers, and the forwarding plane handles the processing, which can lead to high CPU utilization. In asynchronous mode, BFD control packets are sent periodically between peers, and the control plane handles the processing. Asynchronous mode is less CPU-intensive compared to echo mode. Thus, implementing BFD asynchronous mode between peers with low CPU resources can help reduce the CPU load on these network devices.

"...Finally, “BFD can use the slow timer to slow down the asycnhronous session when the echo function is enabled and reduce the number of BFD control packets that are sent between two BFD neighbors.” That is, BFD echo can go fast without interrupting the CPU, and since that will detect an outage, you don’t need BFD control packets running as often, since the control packets aren’t being used for the rapid detection function. That in turn lightens the CPU load and allows more use of BFD. Clever!" Source: https://netcraftsmen.com/clarifying-bfd-and-bfd-echo/

SLow timers is correct. https://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/5_x/nx-os/interfaces/configuration/guide/if_cli/if_bfd.html Unde BFD echo function " BFD can use the slow timer to slow down the asycnhronous session when the echo function is enabled and reduce the number of BFD control packets that are sent between two BFD neighbors. "