Description Of Ipv4 Header Fields

For the first section of this Mid Term, I will describe the fields in the IP version 4 (IPv4) packet header. (What is the structure (each field) of an IPv4 packet?). The first field is a 4-bit version field. Next we have a 4-bit Internet Header Length (IHL) that tells the number of 32-bit words in the IPv4 header. The next field is an 8-bit Type of Service (ToS) field. This technology was never fully implemented so new technology has been developed to utilize this portion of the header. It now relays the DiffServ and Explicit Congestion Notification (ECN) to help the reliability of real time data streaming technologies. The Total Length filed is next. This is a 16-bit field that shows the entire datagram size including header and data, in 8-bit bytes. Next we have a 16-bit Identification field. This field is used primarily to uniquely identify fragment of an original IP datagram. A 3-bit field to control or identify fragments is next. This field must either be zero for reserved, don't fragment, and more fragments. The fragment offset field in next and is a 13-bit field used to determine the particular place of a fragment in the original IP datagram. The 8-bit Time to Live (TTL) field follows. This field stops a datagram from going in circles on a network. It used to be measured in seconds, but is now a hop count field. Once the field comes to zero after passing each switch or router, the packet is no longer forwarded. The 8-bit protocol field follows to show the protocol used in the data portion of the datagram. There are predestinated values for different protocols such as ICMP (1), TCP (6), and UDP (17). Next is the 16-bit header Checksum field. Since some values in an IPv4 header may change, the checksum must be adjusted through the network. Following the checksum field there is a 32-bit Source address field directly followed by another 32-bit Destination address field. Finally, before the data, there can also be additional header fields called Option fields. These fields, though, are not commonly used.

Next we will cover the topics of circuit bandwidth and network throughput. When dealing with networks and data systems, people often get these two terms confused. Circuit bandwidth deals with an analog system, and a mathematical function of time. It is the width, measured in hertz, of a frequency range in which the signal's Fourier transform is nonzero. This definition can also be used to express that the bandwidth would be the range of frequencies that are above a certain threshold in the frequency domain. This inherently uses the bandwidth of a signal to measure how rapidly it fluctuates with respect to time. When talking about digital systems, the work bandwidth is also used, but it is in reference to how much data can be transferred through a digital connection in a given time. This does not really correlate to the actual definition of bandwidth, as it is to measure the fluctuation of a signal with respect to time. So when dealing with digital systems, and referring to the amount of data that is being transmitted, the actual term that should be used is the term network throughput. This is the actual measure of data that is transmitted through a digital system as a relation to time. Throughput is generally measured in bits or bytes per second. This would be the connection's bit-rate.

The Domain Name System (DNS) is the next topic up for discussion in this paper. The DNS is a system that stores information about hostnames and domain names over a distributed network such as the Internet. More importantly the DNS provides a physical (IP address) for each domain name as well as email exchange servers for accepting email for each domain. This allow end users to work with domain names hostnames in URLs and email addresses instead if learning the specific IP addresses that computer and network hardware need to perform addressing and routing tasks. To understand how DNS works, you must understand the major components of the entire system. One of the most important and crucial component of the DNS are the root servers. These are the servers that maintain the base information about DNS locations for specific domains. When asked by a recursive DNS server, which is used by DNS resolver Client side program to search for queries from the resolver on the DNS, the root server delivers the domain authoritative DNS server, or the domain server for that query's specific domain. This will lead the recursive DNS server to the correct domain server, which will then lead to the correct local DNS server. To understand this better, you can look at the DNS as a tree. DNS is a tree of named domains. Each level of the tree is represented by either a branch or a leaf. The branches are levels where there are multiple names used to identify collections of named resources. The leaves are single names used once at that level to indicate a specific resource. There are many different types of "branches" and "leaves" used to store different records in the DNS. SOA records are Start of Authority records and are used to specify the DNS server providing authoritative information about an Internet Domain. NS records, or Name Server records, are used to map a domain name to a list of DNS servers for that domain. A, or address records map a hostname to its 32-bit IPv4 address. PTR record is a pointer record that maps an IPv4 address to the canonical name for that host. And finally, a CNAME is a Canonical Name record that makes one domain name as alias of another.

Next we will look at some different IP routing protocols. We will look at six protocols and explain them in further detail:

1. RIPv1: This stands for Routing Information Protocol version 1. It is a distance-vector routing protocol, and uses classful routing protocols.

2. RIPv2: This stands for Routing Information Protocol version 2. It is a distance-vector routing protocol, and uses classless routing protocols.

3. EIGRP: Stands