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Homework Help: What can be the answer for this question -- Datapath through 3 routers

  1. Nov 23, 2014 #1
    • Member warned about non-descriptive thread title
    1. The problem statement, all variables and given/known data
    An IP machine Q has a path to another IP machine H via three IP routers R1, R2, and R3.
    H acts as an HTTP server, and Q connects to H via HTTP and downloads a file. Session layer
    encryption is used, with DES as the shared key encryption protocol. Consider the following four
    pieces of information:

    [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

    Which of I1, I2, I3, and I4 can an intruder learn through sniffing at R2 alone?

    (A) Only I1 and I2
    (B) Only I1
    (C) Only I2 and I3
    (D) Only I3 and I4

    2. Relevant equations

    3. The attempt at a solution
    As Router works only at Network Layer (which is on top of link layer) of TCP/IP Protocol Stack. Hence option (d) seems appropriate. But correct ans is (c) how
  2. jcsd
  3. Nov 23, 2014 #2


    Staff: Mentor

    you cant encrypt the tcp numbers as they are used to rout your data. You need the host # and port # to talk to the machine after that every else can be encrypted.
  4. Nov 24, 2014 #3
    @jedishrfu then what ans would you suggest.
  5. Nov 24, 2014 #4


    Staff: Mentor

    What answer does it match?
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