Monday, October 10, 2011

iLearn Part 5

Continuing on like a trooper I covered two topics before finishing up tonight. These were Port numbers and the Well Known Port Numbers, then a little more of TCP/IP with how two packets of data traverse a local network and the wider WAN network.

Port numbers are used to distinguish what server/application a host is trying to access, so for example if you open a web browser window and head over to Google, then your PC will have to get that web page from the google server/s. To do this your PC traverses the network (if that server is not on the local network) on it's way to the google web servers, all the time using a target port of 80, which is the well known port for http (the web) and allows the receiving server for example know what service you are trying to get too. Whilst this is the destination port there also needs to be a source port, which is a number that windows dynamically assigns to that specific Chrome, Firefox or IE tab.

I finished off running through some examples of two packets of data, one that only has to worry about finding it's destination on only the Local Area Network with an ARP! The other that has to leave it's LAN and travel the WAN, each time having an element of it's data packet stripped off to allow this to occur until it gets to it's final destination.

The amazing thing is that this happens in a matter of seconds, and not minutes or hours! Great stuff.


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