def find_vnic_by_ip(ip_addr, vnics):
    """
    Given an ip address and a list of vnics, find the vnic that is
    assigned that ip.

    Parameters
    ----------
    ip_addr : str
        The ip address.
    vnics : dict
        The list of virtual network interface cards.

    Returns
    -------
        The matching vnic on success, None otherwise.
    """
    vnic = None
    for v in vnics:
        ip = v['privateIp']
        if ip == ip_addr:
            vnic = v
            break

    return vnic