Why IP and MAC Addresses?

The MAC address is 48bit unique address assigned to any networking/inter networking device, which is embedded on the device and will not change anyway. But the IP may vary each time the device is plugged on to the network (if assigned a dynamic IP address), but there will be only that system on the network with the assigned IP (i.e. address is unique).

MAC address is used only in local communication, i.e. inside a local network only, if it goes out of a network it will use IP address to identify the device/machine.

MAC address is also called Physical address.

As we discussed, the IP address and MAC address are unique, i.e there will be no more than one system with same IP address or same MAC address. So there will be a confusion why to use both addresses?both are unique then why cant use IP or MAC itself?Why both are used in communication?Why the overhead/headache of confusing with both addresses?

Here the answer is,

The MAC address will vary each time the packet of data enters a new network, i.e. the source MAC address and Destination MAC address vary each time the packet reaches a new network, since the physical address is used to locate a system in a local network. The source and destination ip address will remain same always and is not altered with respect to the network changes, the ip should remain same to locate the destination, since the physical (MAC) address varies with network.

Basics of computer Networking

There is no need to say what is computer networking, and what the use of it, all of you will be familiar with that all, so we are not discussing that topics, but just highlighting the basic terms related to computer networking,

1. Different topologies :- Mesh, Ring, Star, Bus
2. OSI Layers :- Physical, Data link, Network, Transport, Session, Presentation, Application
3. Data link sub layers :- MAC (Media Access Control) and LLC (Logical Link Control)
4. IP Address :- Unique 32bit (IPv4)/128bit (IPv6) number assigned to the devices in a network (Including Routers,Switches,Computers etc)
5. Different networking and inter networking protocols :- TCP, UDP, ARP, RARP, ICMP, IGMP, DHCP etc
6. Port numbers :- Port numbers like 80 for http, 21 -ftp, 22 -SSH, 23- Telnet etc
7. MAC Address :- 48bit Physical Address (Unique)
8. Networking and Inter networking devices :- Routers, Hub, Switches, Bridges etc
9. Concept of Routing protocols, Gateways etc
10. Concept of net id, host id, network address, sub netting, super netting, subnet Mask, simplex, half duplex and full duplex modes of communication

There are more terms related to networking, and we are not going through that all, and will discuss whenever necessary in future discussions.

The ip address is unique for the system in a network. An ip address has 2 parts, a network portion and a host portion. Network portion defines in which network that address belongs to; where as the host portion determine the position of that ip within that particular network.The subnet mask has the role of dividing the ip address in to network portion and host portion.

Cabling

the two ends of 8 color wires of Ethernet cable are connected in 3 different ways to for 3 types of cables as below,

Straight through

Orange white - Orange White

Orange - Orange

Green white - Green white

Blue - Blue

Blue white - Blue white

Green - Green

Brown white - Brown white

Brown - Brown

The straight through cables are used to connect dissimilar devices like PC and Hub, PC and Switch etc.

Cross over cable

Orange white - Green white

Orange - Green

Green white - Orange white

Blue - Blue

Blue white - Blue white

Green - Orange

Brown white - Brown white

Brown - Brown

Cross over cables are used to connect similar devices like hub to hub, PC to PC switch to switch etc.

Rolled or Roll over cable

Orange white - Brown

Orange - Brown white

Green white - Green

Blue - Blue white

Blue white - Blue

Green - Green white

Brown white - Orange

Brown - Orange white

Basic Networking Commands

Here is some basic commands used in networking world

1. ping :- ping command is used to check the computer is active in the network(ping IP-address/Computer Name, eg:-ping 192.168.1.1 or ping mydesktop or ping google.com)
2. ipconfig :- to find out the details regarding the active network connection i.e.associated ip address, physical address, subnet mask, default gateway etc (ipconfig/all)
3. netstat :- to find out the different ports active on the system. It displays the port number and protocol(TCP/UDP), local address with port number (local address : port), foreign address(foreign address : port), state (Active or not i.e. connection established or wait), use the command like (netstat)
4. tracert :- it trace the route to a particular computer, for e.g:- if you want find the route to google.com so that you can find whatever IP addresses are involved in accessing google website, or which routers are involved in routing your request to google.com at that particular time(tracert google.com), remember that the table may vary in different intervals of time, the table you got at the moment may/may not be same as the table you will get after few seconds