IP机器Q具有通过三个IP路由器R1，R2和R3到达另一个IP机器H的路径。
Q—R1—R2—R3—H H充当HTTP服务器，Q通过HTTP连接到H并下载文件。使用会话层加密，以DES作为共享密钥加密协议。请考虑以下四个信息：
[I1] The URL of the file downloaded by Q
[I2] The TCP port numbers at Q and H
[I3] The IP addresses of Q and H
[I4] The link layer addresses of Q and H 入侵者可以通过仅嗅探R2来学习I1，I2，I3和I4中的哪一个?
(A)仅I1和I2
(B)只有I1
(C)仅I2和I3
(D)仅I3和I4答案： (C)
解释：
An Intruder can’t learn [I1] through sniffing at R2 because
URLs and Download are functioned at Application layer of OSI Model.
An Intruder can learn [I2] through sniffing at R2 because
Port Numbers are encapsulated in the payload field of IP Datagram.
An Intruder can learn [I3] through sniffing at R2 because IP
Addresses and Routers are functioned at network layer of OSI Model.
An Intruder can’t learn [I4] through sniffing at R2 because
it is related to Data Link Layer of OSI Model.
这个问题的测验