At the end of 11.3.1 Old Duplicate Packets, we claimed that if either side in th

Question

At the end of 11.3.1   Old Duplicate Packets, we claimed that if either side in the TFTP protocol changed ports, the old-duplicate problem would not occur.

(a). If the client changes its port number on a subsequent connection, but the server does not, what prevents an old-duplicate data packet sent by the server from being accepted by the new client?

(b). If the server changes its port number on a subsequent connection, but the client does not, what prevents an old-duplicate data packet sent by the server from being accepted by the new client?

Explanation / Answer

a) TCP connection cannot stay open with a changing port numbeer, because a connection is defined by source ip + port and destination ip + port. In this type of protocol, a logical channel is established between the peers before exchanging the data. So, if the port number will be changed , it will tear down the established connection and re-establishes the connection.

b) The thing is, server never change its port number after accepting the connection.

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