Data encryption PPTP Security

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4.3.3 Multiprotocol Tunneling

The ability to tunnel multiple protocols is one of PPTPs greatest advantages. Some tunneling software allows you to tunnel only IP packets. PPTP, however, can tunnel all of the protocols currently supported by RAS. Users connecting to a RAS server through a VPN will have access to the full range of protocols and servers they would normally have on their LAN. For Windows NT and Windows 9598 users, this means that their usual username and password, and all access privileges associated with their profile, will pertain to the dial-up user. They will be able to browse the network and access file servers and network printers, as always, through their Network Neighborhood.

4.3.4 Ability to Use Corporate and UnregisteredIP Addresses

When VPN users make PPTP connections with the RAS server, they can be assigned IP addresses by that server. The address can be part of the corporations range of IP addresses 2.1.1.129 is part of the 2.1.1.024 CIDR address range in our earlier examples, thus making the RAS users system appear to be on the corporate IP network. Sometimes corporations dont use what are known as registered IP addresses on their internal networks. If a block of addresses is registered, it means that it was obtained by an address registry such as the InterNIC that assures that the addresses are unique on the Internet. The Internet Assigned Numbers Authority IANA has set aside blocks of unregistered IP addresses for use on private internets, or Intranets. These addresses can be used on IP networks that dont have Internet access or that have access through a router that uses Network Address Translation or NAT, which well discuss more later. A listing of these unregistered blocks of addresses can be found in RFC 1918. If a company is using an unregistered range of addresses, a RAS client using PPTP can obtain one of these addresses and have access to the corporate IP network. If the user were simply dialing into an ISP and attempting to access the network without PPTP, a hole in the corporate firewall would have to be opened up for that user. If the user obtains a dynamic IP address whenever they dial into their ISP, this would be nearly impossible.