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Autosave: 2024-09-03 08:00:03

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thomasabishop 2024-09-03 08:00:03 +01:00
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zk/Link_Layer_of_Internet_Protocol.md
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@ -25,7 +25,7 @@ same is not true for other layers. For example a device like a laptop
participates in all four layers up to the Application Layer but a network router participates in all four layers up to the Application Layer but a network router
does not: does not:
![Link Layer diagram](../img/link-layer-internet-diagram.png) ![Link Layer diagram](../img/link-layer-frame-revised.png)
## MAC addresses ## MAC addresses

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zk/Transport_Layer_of_Internet_Protocol.md
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@ -1,6 +1,6 @@
--- ---
title: Transport_Layer_of_Internet_Protocol title: Transport_Layer_of_Internet_Protocol
tags: [] tags: [internet, networks, ports]
created: Tuesday, September 03, 2024 created: Tuesday, September 03, 2024
--- ---
@ -18,3 +18,37 @@ Protocol** (TCP).
A TCP **fragment** fits within an IP packet's data section, giving us the A TCP **fragment** fits within an IP packet's data section, giving us the
following iteration of the network stack: following iteration of the network stack:
![Transport layer fragment](../img/transport-layer-segment.png)
The segment header contains a destination network port number. The port number
identifies the specific service or process on the host device which will receive
the data.
A useful analogy:
_The IP address is like the street address of an office building. The port
number is like the office number of a specific worker within the building. Once
a letter arrives at the building, the mail processing office (like the OS) is
not the intended recipient. Instead the mail worker passes on the letter to the
intended recipient. Likewise, the OS examines the port number and delivers the
inbound data to the process listening on the specified port._
## Ports
A host with a single IP address can have multiple active ports, each used for
performing a different type of activity on the network.
Both servers and clients possess ports. A server will have a dedicated port
which it listens for requests on (typically port 80 or port 443). A client will
have an "ephemeral" port where it listens for responses from a server. They are
ephemeral because they are open only temporarily to receive a response to a
certain request and are assigned dynamically by the networking components of the
OS.
An IP address plus a port (e.g: 192.168.2.1:3000) constitutes an **endpoint**.
An instance of an endpoint is a **socket**.
If multiple clients connect to the same endpoint each has its own socket (for
instance on a host that is a server). A socket can listen for new connections or
it can represent an established, ongoing connection.