I'll over-simplify it:
Information travels along cables to and through various points called nodes.
The first part of an IP address indicates the network node, and the last part indicates the host node.
A subnet mask indicates how many networks an IP address range is divided into and how many hosts can be on that subnet.
A default gateway address is the internal (LAN) address to a node that leads to another network.
A typical home LAN will have a PC with an address of say 192.168.1.100and a router with an address of 192.168.1.1. These are private addresses because the powers that be said that all addresses between 192.168.0.0 and 192.168.255.255 would be private. Private IP addresses can not be routed through the internet. So when you try to access or retrieve something from the Internet your PC says, "Hey this address is not local; send that through the default gateway." The default gateway happens to be a router with a great little thing called NAT. NAT, or Network Address Translation says, "Hey Mr. Packet, you can't go out looking like that - you only have a private IP on!" NAT, being the nice guy he is, loans Mr. Packet his public (WAN) IP address.
I'm being silly in the hope of easing the understanding. Again, this is over-simplified.
Want to have some fun with it now? Go to http://www.ipchicken.com/ and get your current IP address. open a command prompt (as administrator) and type ipconfig do the two match? Now ping both IPs. You should have replies ( type: ping 192.168.1.100 but substitute your IP). Ping yahoo.com and you should also get a reply. Unplug the WAN cable. Can you still ping all these addresses? Use the trace route command; type tracert followed by an address.
Hope this answers your question. If you have a specific problem you are working on I can get more specific.
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What is the difference between IP Address, Subnet Mask, and Default Gateway
ip address is an unique address for an pc/laptop to communicate with an another pc/laptop through internet r Internet.The IP address is divide by using the Subnet mask only
Subnet Mask is used to reduce the ip's wastages ,totally their are three usable classes CLASS A(range 1-127) ,CLASS B(range128-191), CLASS C(range 192-223)
In CLASS A totally 1,67,77,216 ip's are presented like wise in CLASS B 65536 and CLASS C 256 only......
for example- Assign that you are using the class c in that you want only 64 ip's among 256 ,in this case u want to use the subnet mask to subdivide the ip address
Gateway - For every pc/laptop their must be an gateway address through that only we can communicate with the internet which also belongs to the same subnet mask of an ip address