The original LCP standards sent out a LACP protocol packet every 30 seconds; if a LACP packet is not received three times then the link is deemed unusable. This may result in up to a 90 second delay before a problematic link is removed from the port channel.
An amendment was made to the standards so that LACP packets are sent every 1 second. This amendment is known as LACP fast as it means a faulty link can be identified in 3 seconds instead of 90.
LACP Fast can enabled on member interfaces with the command
lacp rate fast. Both ends of the link need to have this command enabled in order for the link to successfully come online.