So let's take a look at the way most Unix systems handle Usenet news. News begins when users create and post articles. Each user enters a message into a special application called a newsreader, which formats it appropriately for transmission to the local news server. But it's also possible to write the article directly into a file in a special directory called the news spool. Once the posting is delivered to the local news server, it takes responsibility for delivering the article to other news users.
News is distributed through the net by various transports.
The medium used to be UUCP, but today the main traffic is carried by Internet sites. The routing algorithm used is called flooding . Any article generated or received by the local news system is forwarded to them, unless it has already been at that site, in which case it is discarded. This header contains a list of all systems through which the article has been forwarded in bang path notation. For each article processed, the news system logs this ID into a history file, against which all newly arrived articles are checked.