老李分享：使用 Python 的 Socket 模块开发 UDP 扫描工具2
编写消息头解码器
开发 IP/ICMP 消息头解码器。脚本创建了一个 sniffer socket，然后在循环中持续读取数据包并进行解码。
注意代码中将 IP 头的前20个字节读取到了缓存，然后再打印消息头的变量。
ICMP 头数据如下：
import socket
import os
import struct
import ctypes
from ICMPHeader import ICMP
# host to listen on
HOST = '192.168.xxx.xxx'
def main():
socket_protocol = socket.IPPROTO_ICMP
sniffer = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket_protocol)
sniffer.bind(( HOST, 0 ))
sniffer.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1)
while 1:
raw_buffer = sniffer.recvfrom(65565)[0]
ip_header = raw_buffer[0:20]
iph = struct.unpack('!BBHHHBBH4s4s' , ip_header)
version_ihl = iph[0]
version = version_ihl >> 4
ihl = version_ihl & 0xF
iph_length = ihl * 4
ttl = iph[5]
protocol = iph[6]
s_addr = socket.inet_ntoa(iph[8]);
d_addr = socket.inet_ntoa(iph[9]);
print 'IP -> Version:' + str(version) + ', Header Length:' + str(ihl) + \
', TTL:' + str(ttl) + ', Protocol:' + str(protocol) + ', Source:'\
+ str(s_addr) + ', Destination:' + str(d_addr)
buf = raw_buffer[iph_length:iph_length + ctypes.sizeof(ICMP)]
icmp_header = ICMP(buf)
print "ICMP -> Type:%d, Code:%d" %(icmp_header.type, icmp_header.code) + '\n'
if __name__ == '__main__':
main()
我们运行 traceroute看下数据包情况：
$ traceroute www.google.com
traceroute to www.google.com (74.125.226.50), 30 hops max, 60 byte packets
1 * * *
2 * * *
3 67.59.255.137 (67.59.255.137) 17.183 ms 67.59.255.129 (67.59.255.129) 70.563 ms 67.59.255.137 (67.59.255.137) 21.480 ms
4 451be075.cst.lightpath.net (65.19.99.117) 14.639 ms rtr102.wan.hcvlny.cv.net (65.19.99.205) 24.086 ms 451be075.cst.lightpath.net (65.19.107.117) 24.025 ms
5 64.15.3.246 (64.15.3.246) 24.005 ms 64.15.0.218 (64.15.0.218) 23.961 ms 451be0c2.cst.lightpath.net (65.19.120.194) 23.935 ms
6 72.14.215.203 (72.14.215.203) 23.872 ms 46.943 ms *
7 216.239.50.141 (216.239.50.141) 48.906 ms 46.138 ms 46.122 ms
8 209.85.245.179 (209.85.245.179) 46.108 ms 46.095 ms 46.074 ms
9 lga15s43-in-f18.1e100.net (74.125.226.50) 45.997 ms 19.507 ms 16.607 ms
会得到这种输出 (注意 ICMP 的响应类型):
sudo python ip_header_decode.py
IP -> Version:4, Header Length:5, TTL:252, Protocol:1, Source:65.19.99.117, Destination:192.168.1.114
ICMP -> Type:11, Code:0(...)IP -> Version:4, Header Length:5, TTL:250, Protocol:1, Source:72.14.215.203, Destination:192.168.1.114
ICMP -> Type:11, Code:0
IP -> Version:4, Header Length:5, TTL:56, Protocol:1, Source:74.125.226.50, Destination:192.168.1.114
ICMP -> Type:3, Code:3
IP -> Version:4, Header Length:5, TTL:249, Protocol:1, Source:216.239.50.141, Destination:192.168.1.114
ICMP -> Type:11, Code:0(...)IP -> Version:4, Header Length:5, TTL:56, Protocol:1, Source:74.125.226.50, Destination:192.168.1.114
ICMP -> Type:3, Code:3
开发扫描器
在编写完整的扫描器前首先要安装 netaddr，它是一个用于表示和处理网络地址的 python 库。
Netaddr 提供了操作 IPv4，IPv6 和子网 Mac 等地址的能力。它非常有用，因为我们会用到子网掩码，如192.168.1.0/24$ sudo pip install netaddr
我们可以使用如下的代码段来测试这个库 (成功会打印“OK”)：
import netaddr
ip = '192.168.xxx.xxx'
if ip in netaddr.IPNetwork('192.168.xxx.0/24'):
print('OK!')