• Tunneling protocols connect dissimilar or separated networks over other networks.binary code digital tunnel background image by Stasys Eidiejus from Fotolia.com
  
  Networks are designed to use specific network protocols to effectively and efficiently transfer information from one computer to another. When two separated networks must communicate by sending information over an untrusted or incompatible network, such as the Internet, tunneling protocols are used. Tunneling protocols repackage or encapsulate the information so that it can be protected from prying eyes while allowing servers on incompatible networks to know where to send it.
  
  

IP-to-IP

• IP-to-IP tunneling is a form of tunneling that allows one IP protocol to be encapsulated by another. An example of this is IPv6 over IPv4. Both IPv4 and IPv6 protocols are valid IP protocols, but not all servers know what to do with the newer IPv6 protocol. When an IPv6 packet is to be sent over the Internet, it must first be encapsulated using the IPv4 IP protocol so that any servers on the Internet along the way know where to send it. When the packet reaches the destination network, the IPv4 package is unwrapped, or unencapsulated, returning it to the original IPv6 format for final delivery.
  
  

Point-to-Point Tunneling Protocol

• PPTP is the most widely used among Windows clients because the client software is built into most of the Microsoft operating systems. This makes it a favorite among system administrators because they do not need to install additional software to make it work. Due to the widespread use of the Windows operating systems, many manufacturers and developers have included PPTP support in their products. The protocol uses the same authentication types as PPP (CHAP, PAP, MS-CHAP, EAP, and SPAP). To provide encryption, the Microsoft Point-to-Point Encryption (MPPE) protocol is used in conjunction with PPTP.
  
  

Layer 2 Forwarding Protocol

• The L2F tunneling protocol is a Cisco Systems developed protocol. Its purpose was to use tunneling of PPP over IP (the Internet) that would allow virtual dial-up links to be created over a network. It relied on other protocols to provide encryption and confidentiality. It has since been replaced by the L2TP tunneling protocol.
  
  

Layer 2 Tunneling Protocol

• The L2TP tunneling protocol is a combination of the PPTP protocol and the L2F protocol. It is not limited to IP networks, but can be used over ATM, frame relay and X.25 networks. Through the use of a security protocol, IPSec, L2TP can provide not only data integrity like PPTP, but also authentication of origin and replay protection. This means the information is verified to be unchanged, the person sending it is the person they say they are and hackers can't capture packets and send them back to the server at a later time to establish a connection of their own under the pretense of being another user or computer.