/**
 * Neighbour Unreachability Detection (NUD) states.
 * @category Constants
 */
export declare enum NudStates {
    /** The neighbour entry is valid forever and can be only be removed administratively. */
    Permanent = "permanent",
    /**
     * The neighbour entry is valid.
     * No attempts to validate this entry will be made but it can be removed when its lifetime expires.
     */
    Noarp = "noarp",
    /** The neighbour entry is valid until the reachability timeout expires. */
    Reachable = "reachable",
    /**
     * The neighbour entry is valid but suspicious.
     * This option to `ip neigh` does not change the neighbour state if it was valid and the address
     * is not changed by this command.
     */
    Stale = "stale",
    /**
     * This is a pseudo state used when initially creating a neighbour entry or after trying to
     * remove it before it becomes free to do so.
     */
    None = "none",
    /** The neighbour entry has not (yet) been validated/resolved. */
    Incomplete = "incomplete",
    /** Neighbor entry validation is currently delayed. */
    Delay = "delay",
    /** Neighbor is being probed. */
    Probe = "probe",
    /** Max number of probes exceeded without success, neighbor validation has ultimately failed. */
    Failed = "failed"
}