Port numbers can take values up to Most of the common applications are assigned well-known port numbers between 1 and port number 0 is reserved. Port numbers through are registered port numbers, while port numbers through define dynamic port numbers automatically assigned by network devices. Port numbers are used to distinguish between applications running on the same device.
Examples of well-known port numbers include the following:. When a TCP connection is established, it follows a process called a three-way handshake.
Host A sends a segment with the SYN bit set, letting the other device know it wants to synchronize. The segment includes the initial sequence number of 5 that Host A is using.
Host B accepts the segment to establish a session and sends back a segment with the SYN bit set. The acknowledgement number represents the next segment it expects to receive, which is 6 this is also called an expectational acknowledgment. The new segment includes the initial sequence number of Host B, which is Host A replies with an ACK segment that contains a sequence of 6, because this is what Host B is expecting, and acknowledgement number 15, informing Host B that it can send the next segment.
The window size informs the remote host about the number of bytes a device will accept before it must send an acknowledgement. However, the window sizes may not match on the two endpoints. Host A has a window size of 2 and Host B has a window size of 3. When Host A sends data, it can send 3 bytes before waiting for an acknowledgement, whereas Host B can send only 2 bytes before receiving an ACK. Note : The window size specifies the number of bytes octets a device will accept, not the number of segments.
After all the data is sent between the two hosts, the session can be closed. The segment includes the sequence number Host B is using at that specific moment, which is Lesson 32 - What is default gateway. Lesson 35 - What is loopback address. Lesson 36 - What is localhost. Lesson 40 - Class D multicast addresses. Lesson 41 - Link-local multicast addresses. Lesson 42 - Internetwork control block multicast addresses. Lesson 43 - Source-Specific Multicast addresses. Lesson 45 - Administratively scoped multicast address block.
Lesson 46 - What is multicast. Lesson 47 - What is multicast group. Lesson 49 - Comparison of multicast with unicast and broadcast. Lesson 50 - Advantages and disadvantages of multicast. Lesson 51 - How IPv4 multicast works. Lesson 52 - IPv4 address reservations. Lesson 60 - Supernetting. Lesson 65 - ICMP message types. Lesson 76 - Ping command tool. Lesson 77 - Ping commmand options.
Lesson 78 - How to show remote computer name in ping command output. Lesson 79 - How to ping continuously. Lesson 80 - How to specify the number of packets sent in ping command. Lesson 81 - How to specify the size of data to send in ping command. Lesson 82 - What is Ping of death PoD. Lesson 84 - Tracert commmand options. Lesson 85 - Pathping command tool. Lesson 86 - Pathping commmand options.
Lesson 89 - IGMP message types. Lesson 96 - Transport Layer Layer 4. Lesson 99 - What port numbers, socket numbers, well-known ports and dynamically assigned ports. Lesson - Multiplexing and Demultiplexing using port numbers. Lesson - UDP pseudo header. Lesson - Application Layer Layer 5. Lesson - How to use telnet command on Windows and telnet command options. Lesson - History of SSH protocol. Lesson - SSH Components.
Lesson - What is SSH host key. Lesson - How SSH works. Lesson - Port forwarding using SSH. Lesson - How to configure SSH port forwarding.
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