Exploration 1 module 5. Network layer.
Network layer encapsulates segments into packets for transmition over the network.

It performs:
Addressing
Encapsulation
Routing
Decapsulation

Each device has an address, on an ip network when a device gets an address it is called a host.

When layer 3 is encapsulated network addresses are added, source and destination.
After data is encapsulated into packets it is sent down to the data-link layer for transmition across the medium.

Network layer also must route packets as devices may be on different networks.

Each router packet passes through is called a hop.

Examples of network protocols include Ipv4 Ipv6 ipx/spx, appletalk and decnet.

IPv4 is connectionless, best effort and media independant.

IP is not reliable it is up to higher level protocols to handle this this reduces overheads.

Network hosts are separated into groups to make networks manageable.
sub groups of networked hosts are called subnets.
groups by locations, ownership and purpose.

Note if you have high network usage say graphic design group they might need their own smaller network so they don't impact other users.

Large numbers of hosts can impact performance example broadcast storm.
Define broadcast domain.
routers segment broadcast domains.

firewalls aid security on networks limit traffic flow.
deviding networks up allows hosts to not need to know all addresses.

Gateway is the way off current network.
hierarchical addressing uses network portion to route packets across network boundaries.

routing: static routes and dynamic routes.
Router needs to know how to get to other devices on the network.

routes have destination address, next hop and metric.