Why are 65535 logical ports? [closed]

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Why are 65535 logical ports? [closed]

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Do I need to know where that number comes from or why does that make the logical ports, why do you need that number of logical ports?

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asked by El Gato Curioso 01.11.2018 в 18:06

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The protocols UDP and TCP have fixed information in their headers including Source Port and Destination Port . Both have a fixed length of 16 bits (2 bytes) each.

Source Port : Unsigned 16-bit integer.
Destination Port : Unsigned 16-bit integer.

Here is a representation of a part of the header:

0                   1                   2                   3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Puerto Origen         |        Puerto Destino         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...

Taking into account the above we can see that the number of available ports range from 0 to 2 ^ 16 - 1 since 2 ^ 16 is the maximum number of ports available in base 2 and whose base is used to represent these values.

For example, this is the sequence of values from 0 to 2 ^ 16 - 1:

(0000 0000 0000 0000) en base 2 = (    0) en base 10
(0000 0000 0000 0001) en base 2 = (    1) en base 10
....
(1111 1111 1111 1111) en base 2 = (65535) en base 10

And as they comment port 0 is reserved according to the IANA although SpeedGuide.net also makes the following note:

This port is technically illegal, but it is possible. It is often used to identify machines, because different operating systems respond to this port in different ways.