The fifth week of CST 311 focused on the network layer.
The network layer only has one protocol, though it is arguably the most important protocol of the Internet – IP. The Internet Protocol (IP) handles two important processes, called routing and forwarding, which control how data moves between endpoints:
- Routing: Determines the path a packet takes from its source
to its destination based on the network’s routing protocols.
- Forwarding: Moves (forwards) a packet from an input link of a switch to an output link of the switch.
One of the essential parts of the Internet Protocol is the concept of an “IP address.” IP addresses work similarly to real-life building addresses. With an address, you can use various tools to look up where the address is located, and then plot a path to it. IP addresses are much the same, where the information contained in the sections of an IP address allow routers to decide which output link to forward a network datagram to.
The first N bits of an IP address specify a subnet mask, which is a globally unique designation of a “subnetwork.” Routers use the subnet prefix of an IP address to determine routing / forwarding decisions. The last N bits of an IP address specify the specific host on that subnet, which allows the last-hop router to determine the final forward operation.
Additionally, there are several IP address ranges that are considered private. Private addresses have no meaning to the wider Internet – they are non-unique, and cannot be used to specify a machine outside of the current subnet. These ranges are:
- 10.0.0.0 to 10.255.255.255
-
172.16.0.0 to 172.31.255.255
- 192.168.0.0 to 192.168.255.255