TRANSPORT LAYER
INTRODUCTION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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1 always
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0 always
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random generated number
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last connection last sequence no
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Detailed explanation-1: -All bytes in a TCP connection are numbered, beginning at a randomly chosen initial sequence number (ISN). The SYN packets consume one sequence number, so actual data will begin at ISN+1. The sequence number is the byte number of the first byte of data in the TCP packet sent (also called a TCP segment).
Detailed explanation-2: -The Initial Sequence Number (ISN) used in TCP/IP sessions should be as random as possible in order to prevent attacks such as IP address spoofing and session hijacking.
Detailed explanation-3: -When a host initiates a TCP session, its initial sequence number is effectively random; it may be any value between 0 and 4, 294, 967, 295, inclusive. However, protocol analyzers like Wireshark will typically display relative sequence and acknowledgement numbers in place of the actual values.
Detailed explanation-4: -In TCP, one purpose of 3-way-handshake is to exchange initial sequence number for both sides. So why not use 0 instead, and the exchange is not necessary. That is to say, sequence numbers can be determined without the 3-way-handshake.