TCP/IP Protocols
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TCP / IP: A Brief Introduction
Transmission Control Protocol (TCP), is a method by which computers can talk to each other, layered upon the Internet Protocol (IP), the low level, switched packet protocol that sets the standard for how data are formatted, so that they can be delivered across a network from one destination to another.
The architecture used in this protocol is known as a layered abstraction network, loosely based on the Seven Layer OSI model, but which actually fits more into the 4 layer DoD model. However, the OSI model is the reference guide on which all networks are based.
Each computer that is going to belong to a network, and thus communicate with other computers, needs an identification code assigned to it, to distinguish it from other computers on the network(s). This is known as an IP Address, and may be automatically assigned dynamically (randomly as needed), by a computer known as a DHCP (Dynamic Host Control Protocol) Server, or have a static address assigned manually, which does not normally change. When a static IP address is assigned to a computer, it is bound to the MAC address which is hard-wired into the chipset of a NIC (Network Interface Card), but may be subsequently re-assigned to a different NIC if required.
An IP Address is a dotted decimal number. The dots split up the number into several separate sections or entities. Thus, the example IP address in our guide (192.168.5.40) is 192 dot 168 dot 5 dot 40 referring to 4 separate entities, and not to the single number 192168540.
Each computer that is connected to the Internet must have a Public, routable IP address. This is an IP address that a connection can be made to from anywhere on the network, and that can have packets of data routed to it.
If you are setting up the entire network from scratch, you will be able to choose the range of IP addresses you wish to allocate to the computers in the network, from certain predefined ranges, as seen in the table in screenshot 3:
Within each of these Classes, there is a set of non-routable private IP addresses that may be used within private company or home networks.
Each network class also contains subnets. A subnet is a grouping of IP addresses located on a single part of a connected network. This is needed so that routers can distinguish between the different parts of a network, and will know exactly where to route the packets of data.
The method of informing the NIC which subnet it is on, is by supplying a subnet mask upon configuration, as shown below:
Class Subnet Mask
Class A 255.0.0.0
Class B 255.255.0.0
Class C 255.255.255.0
The first and last addresses of a subnet (0 and 255 respectively), are used for network broadcast functions, so each subnet can have computers with IP addresses of 1-254.
A Class C network is also called a /24 network, because the network part of the address uses 24 bits.
As mentioned above, if a network is going to communicate with other networks, either internal or external (for example The Internet), it will require a router which has it’s own IP address within the network, as well as a public IP address, and is known as the default gateway. Each NIC has it’s own routing table which tells it where to send packets based on their destination address. It knows that it has to send all packets with destination addresses in it’s own subnet directly to their destination, and that it should send everything else on to the router which becomes the ‘gateway’ out of that subnet and into other networks, by means of it’s own routing tables.
One particular address that is found on every TCP/IP network is that of 127.0.0.1,
commonly known as localhost and the loopback address. This is a virtual network only found on the local machine, and basically allows each computer to communicate with itself using this loopback address.
A domain name is a host name for a computer system that is used in the public internet instead of it’s IP address. Domain Name Servers (primary and secondary) are required in order to use a domain name on the Internet. Most private networks will use their Internet Service Provider (ISP) to provide their DNS for them.
