def pokeMessage(self, ack_key, nb_ipp):
        # If we know about this message, then mark down that this neighbor
        # has acknowledged it.

        try:
            m = self.msgs[ack_key]
        except KeyError:
            # Don't know about this message
            return False

        # Extend the expiration time.
        m.scheduleExpire(self.msgs, ack_key)

        # If not locally-generated, tell the message that this neighbor
        # acknowledged it.
        if nb_ipp:
            m.cancelSendToNeighbor(nb_ipp)

        # Message is known.
        return True