Function getmacbyip

scapy/layers/l2.py:138–193

Returns the destination MAC address used to reach a given IP address. This will follow the routing table and will issue an ARP request if necessary. Special cases (multicast, etc.) are also handled. .. seealso:: :func:`~scapy.layers.inet6.getmacbyip6` for IPv6.

(ip, chainCC=0)

@conf.commands.register
def getmacbyip(ip, chainCC=0):
    # type: (str, int) -> Optional[str]
    """
    Returns the destination MAC address used to reach a given IP address.

    This will follow the routing table and will issue an ARP request if
    necessary. Special cases (multicast, etc.) are also handled.

    .. seealso:: :func:`~scapy.layers.inet6.getmacbyip6` for IPv6.
    """
    # Sanitize the IP
    if isinstance(ip, Net):
        ip = next(iter(ip))
    ip = inet_ntoa(inet_aton(ip or "0.0.0.0"))

    # Multicast
    if in4_ismaddr(ip):  # mcast @
        mac = in4_getnsmac(inet_aton(ip))
        return mac

    # Check the routing table
    iff, _, gw = conf.route.route(ip)

    # Limited broadcast
    if ip == "255.255.255.255":
        return "ff:ff:ff:ff:ff:ff"

    # Directed broadcast
    if (iff == conf.loopback_name) or (ip in conf.route.get_if_bcast(iff)):
        return "ff:ff:ff:ff:ff:ff"

    # An ARP request is necessary
    if gw != "0.0.0.0":
        ip = gw

    # Check the cache
    mac = _arp_cache.get(ip)
    if mac:
        return mac

    try:
        res = srp1(Ether(dst=ETHER_BROADCAST) / ARP(op="who-has", pdst=ip),
                   type=ETH_P_ARP,
                   iface=iff,
                   timeout=2,
                   verbose=0,
                   chainCC=chainCC,
                   nofilter=1)
    except Exception as ex:
        warning("getmacbyip failed on %s", ex)
        return None
    if res is not None:
        mac = res.payload.hwsrc
        _arp_cache[ip] = mac
        return mac
    return None