def find_vnic_by_mac(mac, vnics):
    """
    Given a mac address and a list of vnics, find the vnic that is
    assigned that mac

    Parameters
    ----------
    mac : str
        The MAC address.
    vnics : dict
        The list of virtual network interface cards.

    Returns
    -------
        The matching vnic on success, None otherwise.
    """
    vnic = None
    for v in vnics:
        m = v['macAddr'].lower()
        if mac == m:
            vnic = v
            break

    return vnic