CST 311 Week 5 Journal Entry

Network Layer: Data Plane

This week, we had an introduction to the network layer and learned about the data plane. The network layer has the responsibility of routing data from host to host via segments or packets. When sending data, segments are encapsulated into datagrams that hold the data, and the network adds header information to help with the routing process. Routers use the header information to keep the datagrams in order and determine their next hop. Receiving data is sent from the network to the transport layer and then to the appropriate application. In this process, the network is responsible for forwarding packets from one router to another until it reaches its destination and determining the route that needs to be taken to get packets from one place to its intended destination. 

In the network layer, there are two planes: the data plane and the control plane. The data plane is local and functions in each router. When datagrams arrive at a router, the next port is determined here.  The control plane is network-wide. It is used to determine a datagram's route from the source host to the destination host using two approaches: routing algorithms and software-defined networking. 

Datagrams arrive at the router in the data plane. They first enter the physical layer, then the data link layer, and then the input queue. The datagrams are then forwarded through the appropriate link based on a forwarding table. The data then passes through the switching fabric to the appropriate output buffer, where scheduling policies are used to determine which datagrams are passed through the link layer and physical layer to the next destination. Scheduling policies include First In, First Out, Round Robin, Weighted Fair Queuing, and priority scheduling. 

It is important to know how IP addresses are obtained so that data can move from one host to another. An IP address is a 32-bit identifier for a host or router interface, which is a connection between the host/router and the physical link. In IPv4, dotted decimal notation or binary notation is used for IP addresses. The 32-bit address is divided into 4 bytes, with each byte ranging from 0 to 255. A network IP address consists of a network prefix, a host number, and sometimes a subnet number. A subnet is an interface that shares the high-order bits part of a network's IP address and allows a large network to better use the IP addresses it has. This allows data better routing efficiency by using the available routers provided by the network. A subnet mask allows a host to use part of the network's IP address to communicate over the network. In addition to an address being in IPv4, an address can also be in IPv6. In this form, the header format allows for simpler processing and forwarding. In IPv6, addresses are in hexadecimal notation. Each address is in hexadecimal notation with there being eight 16-bit segments separated by colons. IP addresses that are IPv4 and IPv6 can still operate in a network with a process called tunneling, which allows an IPv4 datagram to embed an IPv6 datagram in its payload and vice versa. This technique allows IPv4 and IPv6 networks to operate with each other. 

Overall, this week was filled with a lot of information. I found the differences between IPv4 and IPv6 interesting in the way that they are represented. Even though they may be different types, they can still cooperate and communicate. The part that took me the longest this week was computing the network address from different IP addresses and subnet masks. I kept writing the incorrect binary number during this worksheet.  I did enjoy the math part of converting to binary and using the AND comparison to determine the network address.