# Routing Between Two Nodes Using IPv4 Addressing

Instructor: Brandon Bass

Brandon has taught Masters and Bachelors courses in Computer Science, Security and Programming. He as a Ph.D in Digital Systems Security and Computer Science.

This is an elementary view of IPv4 and how data is transmitted between two nodes over a network. This lesson will cover topics such as Class C IPv4, RIP, OSPF, and EIGRP.

All networking is simply data communication between computer systems in the basic sense. As a method of communication, IPv4 has been around since 1970. This 32-bit addressing format has been the standard for transmission of information between devices on a network for nearly 50 years. The possible combinations in 32-bit numbers allowed for the mapping of physical devices so that traffic could be sent over the network from one device to another. Think of the IPv4 number as the street address of the computer, and the network mask as the zip code for the area where the computer is located.

## IPv4 Characteristics

IPv4 represents a 32-bit integer or 4 bytes in length. In binary, this is 2^32 or 4,294,967,296 total addresses. IPv4's 4-byte addresses use what is known as dotted decimal notation which has four octets. If you recall, a byte is 8 bits. An octet contains the root word ''octo'' meaning 8. There are 32 bits in the address, so it can be divided into four octets, with periods as delimiters.

## IPv4 Subnetting

A subnet is a way of breaking down an IP network into logical pieces. Standard subnetting for IPv4 uses what is known as a classful subnet. A class C subnet, for example, would use the entire 8-bit address space, producing the maximum number of addresses or 256. A classful class C is common among businesses. The subnet mask is always the number of bits used. For a class C range, the mask has 24 bits on and 8 bits off. The resultant mask for this is range is 255.255.255.0. Each network contains the maximum number of hosts minus 2, because the first address must be the ''network ID'' and the last address must be the ''broadcast ID.''

## How These Nodes Communicate

Once a node has been assigned an address, it can use its send protocols to transmit IPv4 packets. Through a method known as encapsulation, the node will use the IPv4 layer (from the OSI model) to take data segments and encapsulate them into a 32-bit payload. This contains all the necessary information to transmit this data to the node on the other end. The following figure showcases an IP payload header.

While it is unnecessary at this time to understand every piece of the payload, it is important to visualize the 32-packet payload and to know that as this is sent over the network, the data can be analyzed be each node it touches and forwarded on until it reaches the appropriate destination. It also contains data that lets the receiving node know if the full packet has arrived and is corrupted or intact. That way, it can request a re-transmission if there is something wrong with the packet from the source.

IPv4 nodes must have IPv4 addressing schemes as listed. Routing is merely the decision of where to send the payload. Switches will receive the initial payload. If the IPv4 address and subnet of the sender are in the same subnet as the intended recipient, the switch will forward the payload to that node. So, for your computer to send information to your smart TV, they share the same IPv4 subnet of 192.168.0.10 and 192.168.0.111, with a 255.255.255.0 subnet mask.

Anything outside the subnet requires that routers send the information where it needs to go. Routers are configured by network administrators with a series of protocols that ascertain what they are connected to. Then they request information from other routers so they can update their tables. This can be done through protocols.

RIP (Routing Information Protocol) is a method that advertises all routing tables of all things connected to the router every 30 seconds. That way, every connection to each router is constantly updated and the packet can make its way to the appropriate destination.

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