Suppose a user without administrative privileges on client A initiates an SMTP s

Question

Suppose a user without administrative privileges on client A initiates an SMTP session with server S. At the same time, client B also initiates an SMTP session with server S.

a. What is the destination port number of the segments from A to S?

b. What is the valid range of source port numbers of the segments from A to S?

c. If A and B are on different hosts, is it possible that the source port number in the segments from A to S is the same as that from B to S?

d. If A and B are on the same host, is it possible that the source port number in the segments from A to S is the same as that from B to S?

Explanation / Answer

SMTP(Simple mail transfer protocol) is mail server protocol
that uses the port number 25 to transfer mails from this server.

a)
S--->A
The destination port number of segments from A to S becomes 25

b)
A--->S
The valid port numbers are in a range of 0 to 65536 inclusive
for comminication between A to S

c)
Yes. Since port numbers on the client are independent of port
of another client. So if they are different hosts, may
contain same port numbers from A to S and B to S.

d)
No.
If two clients A and B (A and B two different sessions ,simply as two processes ) from same source (host)
then a port number identifies a process associated with port number will identify any process within the host system.

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