def interface_by_macaddr(self, macaddr):
        '''
        Given a MAC address, return the interface that 'owns' this address
        '''
        macaddr = EthAddr(macaddr)
        for devname,iface in self._devinfo.items():
            if iface.ethaddr == macaddr:
                return iface
        raise KeyError("No device has MAC address {}".format(macaddr))
Given a MAC address, return the interface that 'owns' this address