The network layer or Layer 3 is very important to us as a network engineers as this is where routers
reside.
This layer is all about data delivery where routers rot data packets from one device to another.
Cisco and other vendors also have what is called Layer 3 switches Layer 3 switches have router capabilities
so that they can also rot packets between v lands within a network.
As an example routers or Layer 3 devices choose or select the best path to deliver data based on the
information provided by writing protocols such as 0 SPF or open shortest path first or BGP or Border
Gateway Protocol or ISIS or intermediate system to intermediate system.
Those are three examples of routing protocols you may encounter.
They use the logical addressing scheme of IP version 4 to determine the best path.
So in an IP version 4 network we have addresses such as 1 9 2 1 6 8 1 dot 1 with a network mask of 2
5 5 2 4 5 2 4 5 0 the network Mosk informs devices that in this example the first three Tests on network
and that's what writing decisions are made on.
Please refer to the IP addressing videos for more detail about network and host portions of an IP address
so routers or Layer 3 switches will determine the best path to route traffic.
Based on criteria such as the cost or number of hops or bandwidth or longest match of a network address
so various criteria can be used to determine the best route.
So as an example of SPF determines the best path based on bandwidth rope or writing Information Protocol
which is an older routing protocol used hop count to determine the best path but what's important to
know is that writing decisions are based on the logical addressing format in IP vision for or IP version
6.
There is no reliability at the network layer.
IP is not concerned with reliability and relies on the higher layer protocols such as TTP to provide
reliability or if UDP is used.
The application layer needs to provide the reliability if it's required.
So as an example when using TFT P TFT P uses UDP at layer for an IP at Layer 3 but the TFT IP application
provides the reliability because there is no reliability in UDP or in IP so IP does not provide any
reliability or retransmission of packets.
The network layer or Layer 3 provides path determination and logical addressing.