Computer 1 on network B, with IP address of 192.168.1.121, wants to send a packet to Computer 2, with IP address of 10.1.1.8. Taking in consideration that computer 1 is sending a request to a web server on computer 2, listening on port 80, and the source port on computer 1 is 5000, which of the following contains the correct information for the first TCP segment of data?
Source Port: 80
Destination Port: 5000
Sequence Number: 1
Acknowledgment Number: 1
Source Port: 8081
Destination Port: 50
Sequence Number: 4
Acknowledgment Number: 1
Source Port: 5000
Destination Port: 80
Sequence Number: 1
Acknowledgment Number: 2
Source Port: 80
Destination Port: 5000
Sequence Number: 1
Acknowledgment Number: 2
The Correct Answer and Explanation is :
The correct answer is:
Source Port: 5000 Destination Port: 80 Sequence Number: 1 Acknowledgment Number: 2
Explanation:
When Computer 1 (IP: 192.168.1.121) sends a request to the web server on Computer 2 (IP: 10.1.1.8), the first TCP segment will have the following characteristics:
- Source Port and Destination Port:
- The source port is chosen by Computer 1 for the connection, and in this case, it is 5000. This port number is used to identify the originating process on Computer 1 (the client).
- The destination port is 80, which is the well-known port for HTTP. This is the port that the web server on Computer 2 is listening to, expecting incoming requests.
- Sequence Number:
- The sequence number is set to 1 for the first packet because this is the first byte of data that will be transmitted. TCP is a connection-oriented protocol that keeps track of the order of data bytes using sequence numbers.
- Acknowledgment Number:
- The acknowledgment number is set to 2. In TCP, the acknowledgment number indicates the next byte expected from the other party. Since Computer 1 is sending the first request, it is not acknowledging any data yet, but the acknowledgment number is initialized to the value that would be expected once the handshake is completed. In this case, since the sequence number starts at 1, the acknowledgment number would be 2 to indicate that the sender expects to receive the byte after the initial byte.
Why the other options are incorrect:
- Source Port: 80, Destination Port: 5000 – This is incorrect because it would imply the server (Computer 2) is sending a response to Computer 1, and the ports would be reversed after the connection is established, not during the request.
- Source Port: 8081, Destination Port: 50 – This is incorrect because the ports don’t correspond to the normal ports used for HTTP (port 80 for the server, and a dynamically assigned port for the client).
- Source Port: 80, Destination Port: 5000 – Similar to the first incorrect option, this reflects the reverse of the initial request, where Computer 1 would be acknowledging the server’s response after a handshake.
In conclusion, the correct first TCP segment in the request from Computer 1 to Computer 2 has a source port of 5000, destination port of 80, sequence number 1, and acknowledgment number 2.