1. Why
The Maximum-Prefix feature is useful when, at a change of outbound policy at the remote peering site, a router starts to receive more routes than the router memory can take. If this same router is peering with BGP and also performs critical routing functions within a network, this overhead could turn out bad. A BGP problem could disrupt internal network connectivity. With the neighbor maximum-prefix command, it is possible to protect a router against this situation.
Maximum is 10, threshold is 80%, defalut action is turning the peer as IDLE status.