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How does TCP and HTTP work?
A typical use case of TCP is HTTP. Our web browser (application 1) connects to a web server (application 2). Once the connection is made, the browser can send a request through the connection, and the web server can send a response back through the same connection.
What is ACK bit?
When computers communicate via TCP, received packets are acknowledged by sending back a packet with an ACK bit set. The TCP protocol allows these acknowledgments to be included with data that is sent in the opposite direction. Some protocols send a single acknowledgment per packet of information.
Does HTTP work over TCP?
Among the two most common transport protocols on the Internet, TCP is reliable and UDP isn’t. HTTP therefore relies on the TCP standard, which is connection-based.
What is the default value for TCP ACK?
If you set the value to 1, every packet is acknowledged immediately because there’s only one outstanding TCP ACK as a segment is just received. The value of 0 (zero) isn’t valid and is treated as the default, 2.
How does a client send a TCP packet?
The client will send a TCP packet with the SYN (Synchronization) flag set, secondly the receiving server will send its own SYN with the ACK (Acknowledgement) flag also set. This is so it can acknowledge the previous SYN from the client.
Why is the ACK number in packet 1 not incremented?
In the TCP close table, the ACK bits in packet 1 and 3 are not specific to closing TCP sessions, but are needed because part of the general TCP process is to send Ack’s back to the sender with the Ack number set to the expected next sequence number. In packet 2, the server Ack’s the client Fin bit but notice that the Ack # is not incremented by 1.
Which is the first packet to initiate the TCP close?
In the below figure, we see a Wireshark decode of Wireshark packet # 280, which is the first packet sent by the client to initiate the TCP close. Key points include the FIN and ACK flags being set and the capture of the sequence and acknowledgement numbers.