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Ethical Hacking simplified (System fundamentals) OSI reference model

this is the continuation of OSI reference model

for layer 5 to 7 here
 layer 4 here
 

Network layer (layer 3)

This layer take control of the way the network addressing works. It deals with managing IP addressing, tracking device location, and choose the best path to transmit data. Network layer again is after sending data to devices that do not belong the same local network. The Router (also known as layer 3 device) routes packages between different networks.
When a package arrived at layer 3, the router checked the source and destination network address (don't worry we will discuss that later) if it matched? Then the router has nothing to do with it, because they belong to one LAN(local area network i.e. The same network) and router only route packages between different networks or LANs. Take for example, when making a local call (within the same country) do you need and IDD (international direct dialing) number? That +234 stuffs. The ans is definitely no! Why? Because you are calling a local number! What will happen if you include it? The telephone interchange system will definitely discard it and treat it as a local call! That's the same way router will treat local package! Wooh!!! sound simple!

There are two types of packets used at the network layer
  • Data packets
  • Route update packets

Data packets: This packet is used to transport user data in the internetwork, Routed protocols (IP: internet protocol and IPv6: IP version 6) are used to transport data. IP also known as IPv4 is a 32bit long, which represent in mathematics as . which is equal to 4294967296, around 4.3 billion addresses. The IPv6 is 128bit addresses! This cant be represented in figures! If if we do using powerful calculators it can't be read by human because its logically infinity! Due to high use of networks and devices that needs IP addresses are evolving every now and the! The IPv4 is might exhaust, that make it compulsory to come up with solution, and the solution is the IPv6! Will discuss IPv4 and v6 in a separate article, the most important thing here is to know about the technology.

Route update packet: This package is used to update the neighboring routers if a new router is connected to the internetwork. This packet works as an announcer to the internetwork. Good example is, when a new student join you in primary school, the teacher will introduce the student with his name, so as each and every student in the class will know his name. That is what routing packets does! Although routing packets do add addresses after name. The most common protocols here are RIP(routing information protocol), RIPv2(version 2), OSPF(open shortest path first) and EIGRP (Enhanced interior gateway routing protocol). Route protocols maintains a table (Routing table) which keep the records of all the routers connected and how to reach them.



 to be continued
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