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. "