3

背景：

我正在使用scapy解析IEEE 802.1Q triple tagged frames. 我正在使用 scapy 生成测试帧并将它们捕获到 pcap 文件中。解析是通过读入 pcap 文件在单独的脚本中完成的。我可以成功使用第一个 802.1q 标签。

问题：

我不清楚如何访问第二个和第三个 802.1q 标签。我正在尝试使用haslayer()并getlayer有条件地检查帧头。 haslayer(Dot1Q)返回与第一个 Dot1Q 标记关联的值。

问题：

如果type第一个标签的字段是0x8100，则存在第二个标签。有没有办法前进到第二和第三个标签？我查看了 l2.py 源并进行了实验，但还没有运气。

代码：

发送三重标签帧：

    sendp(Ether(dst='78:2B:CB:33:4B:9F',src="D4:AE:52:89:BA:FA")/Dot1Q(vlan=1,id=3,prio=2)/Dot1Q(vlan=2,id=3,prio=2)/Dot1Q(vlan=3,id=3,prio=2)/IP(dst='10.25.222.222')/ICMP())

帧显示：

###[ Ethernet ]###
  dst       = 78:2b:cb:33:4b:9f
  src       = d4:ae:52:89:ba:fa
  type      = 0x8100
###[ 802.1Q ]###
     prio      = 2L
     id        = 1L
     vlan      = 1L
     type      = 0x8100
###[ 802.1Q ]###
        prio      = 2L
        id        = 1L
        vlan      = 2L
        type      = 0x8100
###[ 802.1Q ]###
           prio      = 2L
           id        = 1L
           vlan      = 3L
           type      = 0x800
###[ IP ]###
              version   = 4L
              ihl       = 5L
              tos       = 0x0
              len       = 28
              id        = 1
              flags     = 
              frag      = 0L
              ttl       = 64
              proto     = icmp
              chksum    = 0xc55
              src       = 10.25.123.123
              dst       = 10.25.222.222
              \options   \
###[ ICMP ]###
                 type      = echo-request
                 code      = 0
                 chksum    = 0xf7ff
                 id        = 0x0
                 seq       = 0x0
###[ Padding ]###
                    load      = '\x00\x00\x00\x00\x00\x00'

Frame parsing:

pkts=rdpcap(self.file_name)

for pkt in pkts:

    try:
        if pkt.haslayer(Ether):
            src     = pkt.getlayer(Ether).src
            dst     = pkt.getlayer(Ether).dst
            type    = pkt.getlayer(Ether).type
            # Do something 

        if pkt.haslayer(Dot1Q):
            prio    = pkt.getlayer(Dot1Q).prio
            id      = pkt.getlayer(Dot1Q).id
            vlan    = pkt.getlayer(Dot1Q).vlan
            type    = pkt.getlayer(Dot1Q).type
            # Do something

    except:
        raise `
4

1 回答 1

3

You can access the inner 802.1Q tags of pkt with pkt[Dot1Q:2], pkt[Dot1Q:3] and so on. If the packet doesn't have the specified layer, an appropriate IndexError exception is raised:

In [3]: pkt
Out[3]: <Ether  dst=78:2B:CB:33:4B:9F src=D4:AE:52:89:BA:FA type=0x8100 |<Dot1Q  prio=2 id=3 vlan=1 type=0x8100 |<Dot1Q  prio=2 id=3 vlan=2 type=0x8100 |<Dot1Q  prio=2 id=3 vlan=3 type=0x800 |<IP  frag=0 proto=icmp dst=10.25.222.222 |<ICMP  |>>>>>>

In [4]: pkt[Dot1Q:1]
Out[4]: <Dot1Q  prio=2 id=3 vlan=1 type=0x8100 |<Dot1Q  prio=2 id=3 vlan=2 type=0x8100 |<Dot1Q  prio=2 id=3 vlan=3 type=0x800 |<IP  frag=0 proto=icmp dst=10.25.222.222 |<ICMP  |>>>>>

In [5]: pkt[Dot1Q:2]
Out[5]: <Dot1Q  prio=2 id=3 vlan=2 type=0x8100 |<Dot1Q  prio=2 id=3 vlan=3 type=0x800 |<IP  frag=0 proto=icmp dst=10.25.222.222 |<ICMP  |>>>>

In [6]: pkt[Dot1Q:3]
Out[6]: <Dot1Q  prio=2 id=3 vlan=3 type=0x800 |<IP  frag=0 proto=icmp dst=10.25.222.222 |<ICMP  |>>>

In [7]: pkt[Dot1Q:4]
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-7-a155defcb885> in <module>()
----> 1 pkt[Dot1Q:4]

/usr/local/lib/python2.7/dist-packages/scapy_real-2.2.0_dev-py2.7.egg/scapy/packet.pyc in __getitem__(self, cls)
    770             elif type(lname) is not str:
    771                 lname = repr(lname)
--> 772             raise IndexError("Layer [%s] not found" % lname)
    773         return ret
    774 

IndexError: Layer [Dot1Q] not found

Of course, you may check the type value and only after verifying that it is 0x8100, try accessing the inner layer.

于 2015-01-27T10:35:40.910 回答