用 scapy 在 python 中编写以太网桥

I attempted to build this thing by running a scapy program on B that would sniff ports e and f, and in each case modify the destination IP and MAC address in the packet and then send it along through the other interface. Something like:

my_macs = [get_if_hwaddr(i) for i in get_if_list()]
pktcnt = 0
dest_mac_address = discover_mac_for_ip(dest_ip) # 
output_mac = get_if_hwaddr(output_interface)

def process_packet(pkt):
    # ignore packets that were sent from one of our own interfaces
    if pkt[Ether].src in my_macs:
        return

    pktcnt += 1
    p = pkt.copy()
    # if this packet has an IP layer, change the dst field
    # to our final destination
    if IP in p:
        p[IP].dst = dest_ip

    # if this packet has an ethernet layer, change the dst field
    # to our final destination. We have to worry about this since
    # we're using sendp (rather than send) to send the packet.  We
    # also don't fiddle with it if it's a broadcast address.
    if Ether in p 
       and p[Ether].dst != 'ff:ff:ff:ff:ff:ff':
        p[Ether].dst = dest_mac_address
        p[Ether].src = output_mac

    # use sendp to avoid ARP'ing and stuff
    sendp(p, iface=output_interface)

sniff(iface=input_interface, prn=process_packet)

但是，当我运行这个东西(完整源代码这里)时，各种疯狂的事情开始发生...有些数据包通过了，我什至得到了一些响应(使用 ping 进行测试)，但是有某种类型的反馈循环导致发送一堆重复的数据包...