there are more than one protocols to builda VPN, which depends the desired set of service you want most.

Some companies might be ok to transfer datawith clear text but maintaining integrity is essential to them. The other one is focusing on data confidentiality while integrity is not their first concern.

To build a VPN solution, you might have to put in place certain components which include:

Desktop software for clients

Cisco concentrator or Cisco PIX firewall

Dedicated VPN server for dial up services.

Network Access Service used by serviceprovider for remote access.

Policy management center.

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The blockchain can be a distributed ledger,it can be shared to multiple parties to validate the digital money or transactions that have been digitized.

This feature usually be seen as a killer app, but it actually is one of its characteristics.

Blockchain can also be a software development platform, though it could have brought political and societal underpinnings. But it is with great novelties.

There are many APIs, P2P nodes communications,transaction script language, this function will be discussed more in later chapter.