IP tunneling often bypasses simple firewall rules transparently since the specific nature and addressing of the original datagrams are hidden. It is an Internet Protocol (IP) network communications channel between two networks.
A tunnel is a mechanism used to ship a foreign protocol across a network that normally wouldn't support it. Tunneling protocols allow you to use, for example, IP to send another protocol in the data portion of the IP datagram. Most tunneling protocols operate at layer 4, which means they are implemented as a protocol that replaces something like TCP or UDP. Tunneling uses a layered protocol model such as those of the OSI or TCP/IP protocol suite, but usually violates the layering when using the payload to carry a service not normally provided by the network. Another important use is to provide services that are impractical or unsafe to be offered using only the underlying network services; for example, providing a corporate network address to a remote user whose physical network address is not part of the corporate network. Tunneling, also known as port forwarding, is the transmission of data intended for use only within a private, usually corporate network through a public network in such a way that the routing node s in the public network are unaware that the transmission is part of a private network. An extranet is a private network that uses Internet technology and the public telecommunication system to securely share part of ... See complete definition. Network Address Translation (NAT). A NAT (Network Address Translation or Network Address Translator) is the virtualization of Internet Protocol (IP) addresses. IP Tunneling and VPNs Overview The purpose of this module is to explain Virtual Private Network (VPN) concepts and to overview various L2 and L3 tunneling techniques that allow for implementation of VPNs. The access VPN features in Cisco IOS Release 12.1 are explained along with Layer 2 and Layer 3 tunneling mechanisms. Usually, Layer-3 tunneling is used either to connect two discontiguous parts of a non-IP network over an IP network, or to connect two IP networks over a backbone IP network, possibly hiding IP addressing details of the two networks from the backbone IP network. In IP tunnelling, every IP packet, including addressing information of its source and destination IP networks, is encapsulated within another packet format native to the transit network. Other variants of the IP-in-IP variety are IPv6-in-IPv4 (6in4) and IPv4-in-IPv6 (4in6). IP tunneling often bypasses simple firewall rules transparently since the specific nature and addressing of the original datagrams are hidden. Content-control software is usually required to block IP tunnels With IP-in-IP tunneling, an IP datagram is encapsulated with another IP header addressed to and from the endpoints of the IP-in-IP tunnel, as shown in Figure 4.5. An IP-in-IP tunnel is indicated by setting the IP Protocol field to 4 in the outer IP header. For more detailed information about IP-in-IP tunneling, see RFC 1853. A typical use for IP-in-IP tunnels is the forwarding of IP multicast traffic from one area of the intranet to another area of the intranet, across a portion of the intranet that does not support multicast forwarding or routing. Tunneling is the process in which one layer is encapsulated in the payload of another layer. In the OSI model. IP Tunneling: Suppose you tunnel an ip packet inside another ip packet. On the left you can see the packet to be encapsulated and on the right this packet is added as payload to another IP packet. On the receiving end the process is reversed and the payload packet is sent to the higher layers of stack. IP tunneling can be of many types ip over ip, ip6 over ip, ip over ip6. In TCP tunneling the same process is done at TCP level. TCP tunneling is generally used for port forwarding because traffic can be selectively forwarded based on destination port. Here are some nice articles: IP Tunneling An IP tunnel is an Internet Protocol (IP) network communications channel between two networks. It is used to transport another network protocol by encapsulation of its packets. IP tunnels are often used for connecting two disjoint IP networks that don't have a native routing path to each other, via an underlying routable protocol across an intermediate transport network. Other variants of the IP-in-IP variety are IPv6-in-IPv4 (6in4) and IPv4-in-IPv6 (4in6). IP tunneling often bypasses simple firewall rules transparently since the specific nature and addressing of the original datagrams are hidden. Content-control software is usually required to block IP tunnels
http://www.enterprisenetworkingplanet.com/netsp/article.php/3624566/Networking-101-Understanding-Tunneling.htm https://en.wikipedia.org/wiki/Tunneling_protocol http://searchenterprisewan.techtarget.com/definition/tunneling http://www.net130.com/tutorial/cisco-pdf/1IP_Tunneling_and_VPN_Technologies.pdf https://en.wikipedia.org/wiki/IP_tunnel https://technet.microsoft.com/en-us/library/cc940485.aspx http://superuser.com/questions/378693/difference-between-tcp-and-ip-tunnelling https://en.wikipedia.org/wiki/IP_tunnel
what is ip tunneling