IP Addressing Schema 1 Public vs. Private IP

A public IP address is another name for a static IP address. It is an IP address available for everyone to see. Public IP’s let the general public find out information about your computer and are available to see it, for example a web server.

A private IP address is an IP address used on a private network (e.g. a home network) that is not routable through the public internet. So a private IP address is for security.

Subnet Masks

A subnet allows data traffic between devices to be split, based on their network configuration. The subnet then orders the devices (hosts) into a logical order. For example, on a network, each device that has an IP ending in 6 would be a printer and the subnet would split them from the other IP addresses.

A subnet mask is not part of the IP and it can’t exist separately from the IP, but it works alongside the IP. So when a subnet mask is applied, this splits the IP into 2 parts. A “extended network address” and a “host address”.

A subnet mask (like an IP) is composed of 4 bytes (32 bits) and is often written the same way as an IP, in the “dotted decimal” system. For example, a common subnet mask is 255.255.255.0. Written in binary, this is 11111111 11111111 00000000 00000000. For a subnet mask to be valid, the leftmost piece must be set to “1”. So 00000000 00000000 00000000 00000000 is invalid, because the bit furthest left is not a “1”. But also the furthest right piece must be set to “0”. So 1111111 11111111 11111111 1111111 is invalid. So all valid subnet masks must have the leftmost bit a “1” (a.k.a the “extended network portion”) and the rightmost bit a “0” (a.k.a the “host portion”).

A “default gateway” is a device on a network that passes traffic from the subnet to devices on other subnets. The default gateway is usually that connects the local network to the internet, but internal gateways do exist.

Usually there are 2 types of internet default gateways. The first is found in a home network, where there are devices connected to a router. Here, the router acts as the internet gateway. The second type is found in a home or small business that doesn’t have a router. So this is usually for networks with a dial-up connection. Here, the ISP (internet service provider) acts as the internet gateway.

But a router is not necessarily needed for an internet gateway to be configured. A normal computer can do the job just fine. All that is needed is 2 network adapters, one connected to the local subnet, and another connected to the outside network. This is called a “gateway computer”. In large businesses and networks, either routers or gateway computers can be used to network local subnets together.

So, the major problem with the internet and the amount of devices connected to it at the moment is running out of IP addresses. Now, most IP’s are “IPv4” which is the standard “4 numeral decimal” system, e.g. 172.168.0.1. IPv6 is just like IPv4, but it has more digits, to ensure that there are enough IP’s for a long while.

If a computer has an incorrect IP address entered, then the network won’t recognise the computer and the device simply won’t be able to connect to the network and be able to access the internet. So if a device has trouble connecting to the internet, then the first troubleshoot should be (after checking the connection) is to 1 check the IP configuration.

The consequences of giving a computer a public IP instead of a private IP is that, if it is a private computer (e.g. A home desktop) then everyone on the internet and the network will be able to see your IP address, which can lead to problems with security later on and as this also makes it a static IP, furthermore leaving yourself open to security issues. But on the other hand, if a server in a work environment is given a private IP, then none of the other machines are going to be able to connect to and contact the server very easily. This can also (for obvious reasons) cause major network problems in a work environment.

A consequence that can arise if the subnet mask is incorrect is that all the devices on the LAN may have problems trying to communicate with each other. So each device has to agree on what the subnet mask is, otherwise the above could happen.

If the default gateway is incorrectly configured, then the main consequence is that the internet won’t work. This is because the LAN won’t be able to connect to other networks, which may include the internet.

CSMA/CD (Carrier Sense Multi Access/Collision Detection) is a protocol employed on Ethernet architecture, which monitors traffic and traffic collision on the network. So what CSMA/CD actually does 2 is, it stops a transmission as soon as a collision is detected. This shortens the time that it takes before a re-transmission can be attempted. So its main job is to detect and stop data collision. So in simple terms, what collision detection does is detect when 2 signals are about to collide, and stops the transmission, which shortens the time before transmissions can occur again, as usually, when the data collides, the nodes re-transmit at a random time . Also “carrier sense” works by each Ethernet node on the network will “listen” to the Ethernet cable to see if a device is transmitting. If another transmission is occurring, then the node waits to transmit. CSMA/CD is multi-access, which means that many devices can be listening and waiting to transmit at once.

Collisions occur very simply. So imagine there is a network with only 2 nodes. Both listen to the Ethernet, and hear no transmission. Then they both transmit. The data then collides, so each node waits (independently) and re-transmits at a different time. When there are many nodes transmitting at once, the amount and the rate of collisions on a LAN rise to a very unacceptable level. Since collisions are expected on a network, but only a very small amount, there is an acceptable level of collisions. If the amount and rate of collisions rise over this acceptable level, then the bandwidth gets absolutely shattered in re-transmission. Ethernet switches help a great deal in reducing the amount of collisions that occur on a LAN.

The CSMA/CD protocol gives each node a fair chance to transmit, and does not give higher priority to any other device. So all nodes on the network get a fair chance to use the Ethernet. After the data packet has been transmitted, each node uses the CMSA/CD protocol to determine which station goes next. CSMA/CD is now out-dated technology. CSMA/CD was first introduced when twisted-cable Ethernet was becoming used, but now, nobody uses it anymore, as full-duplex communication was introduced. But CSMA/CD is still occasionally used for backwards compatibility.