使用 scapy 桥接 IP 数据包：
- 首先确保您禁用了 ip 转发，否则会注意到重复的数据包：
echo "0" > /proc/sys/net/ipv4/ip_forward <br>
- 第二次运行以下 python/scapy 脚本：
!/usr/bin/python2
from optparse import OptionParser
from scapy.all import *
from threading import Thread
from struct import pack, unpack
from time import sleep
def sp_byte(val):
return pack("<B", val)
def su_nint(str):
return unpack(">I", str)[0]
def ipn2num(ipn):
"""ipn(etwork) is BE dotted string ip address
"""
if ipn.count(".") != 3:
print("ipn2num warning: string < %s > is not proper dotted IP address" % ipn)
return su_nint( "".join([sp_byte(int(p)) for p in ipn.strip().split(".")]))
def get_route_if(iface):
try:
return [route for route in conf.route.routes if route[3] == iface and route[2] == "0.0.0.0"][0]
except IndexError:
print("Interface '%s' has no ip address configured or link is down?" % (iface));
return None;
class PacketCapture(Thread):
def __init__(self, net, nm, recv_iface, send_iface):
Thread.__init__(self)
self.net = net
self.netmask = nm
self.recv_iface = recv_iface
self.send_iface = send_iface
self.recv_mac = get_if_hwaddr(recv_iface)
self.send_mac = get_if_hwaddr(send_iface)
self.filter = "ether dst %s and ip" % self.recv_mac
self.arp_cache = []
self.name = "PacketCapture(%s on %s)" % (self.name, self.recv_iface)
self.fw_count = 0
def run(self):
print("%s: waiting packets (%s) on interface %s" % (self.name, self.filter, self.recv_iface))
sniff(count = 0, prn = self.process, store = 0, filter = self.filter, iface = self.recv_iface)
def process(self, pkt):
# only bridge IP packets
if pkt.haslayer(Ether) and pkt.haslayer(IP):
dst_n = ipn2num(pkt[IP].dst)
if dst_n & self.netmask != self.net:
# don't forward if the destination ip address
# doesn't match the destination network address
return
# update layer 2 addresses
rmac = self.get_remote_mac(pkt[IP].dst)
if rmac == None:
print("%s: packet not forwarded %s %s -) %s %s" % (self.name, pkt[Ether].src, pkt[IP].src, pkt[Ether].dst, pkt[IP].dst))
return
pkt[Ether].src = self.send_mac
pkt[Ether].dst = rmac
#print("%s: forwarding %s %s -> %s %s" % (self.name, pkt[Ether].src, pkt[IP].src, pkt[Ether].dst, pkt[IP].dst))
sendp(pkt, iface = self.send_iface)
self.fw_count += 1
def get_remote_mac(self, ip):
mac = ""
for m in self.arp_cache:
if m["ip"] == ip and m["mac"]:
return m["mac"]
mac = getmacbyip(ip)
if mac == None:
print("%s: Could not resolve mac address for destination ip address %s" % (self.name, ip))
else:
self.arp_cache.append({"ip": ip, "mac": mac})
return mac
def stop(self):
Thread._Thread__stop(self)
print("%s stopped" % self.name)
if __name__ == "__main__":
parser = OptionParser(description = "Bridge packets", prog = "brscapy", usage = "Usage: brscapy -l <intf> (--left= <intf>) -r <inft> (--right=<intf>)")
parser.add_option("-l", "--left", action = "store", dest = "left", default = None, choices = get_if_list(), help = "Left side network interface of the bridge")
parser.add_option("-r", "--right", action = "store", dest = "right", default = None, choices = get_if_list(), help = "Right side network interface of the bridge")
args, opts = parser.parse_args()
if len(sys.argv) == 1:
parser.print_help()
sys.exit(1)
lif = args.left
rif = args.right
lroute = get_route_if(lif)
rroute = get_route_if(rif)
if (lroute == None or rroute == None):
print("Invalid ip addressing on given interfaces");
exit(1)
if (len(lroute) != 5 or len(rroute) != 5):
print("Invalid scapy routes")
exit(1)
conf.verb = 0
lthread = PacketCapture(rroute[0], rroute[1], lif, rif)
rthread = PacketCapture(lroute[0], lroute[1], rif, lif)
lthread.start()
rthread.start()
try:
while True:
sys.stdout.write("FORWARD count: [%s -> %s %d] [%s <- %s %d]\r" % (lif, rif, lthread.fw_count, lif, rif, rthread.fw_count))
sys.stdout.flush()
sleep(0.1)
except KeyboardInterrupt:
pass
lthread.stop()
rthread.stop()
lthread.join()
rthread.join()
在我的电脑上：
# ./brscapy.py --help
Usage: brscapy -l <intf> (--left= <intf>) -r <inft> (--right=<intf>)
Bridge packets
Options:
-h, --help show this help message and exit
-l LEFT, --left=LEFT Left side network interface of the bridge
-r RIGHT, --right=RIGHT
Right side network interface of the bridge
# ./brscapy.py -l e0 -r e2
PacketCapture(Thread-1 on e0): waiting packets (ether dst 00:16:41:ea:ff:dc and ip) on interface e0
PacketCapture(Thread-2 on e2): waiting packets (ether dst 00:0d:88:cc:ed:15 and ip) on interface e2
FORWARD count: [e0 -> e2 5] [e0 <- e2 5]