The path followed by an IP packet when it is encapsulated in a second IP packet with an alternate IP destination addresses. While it is encapsulated, the internal datagram is protected from normal Internet routing. The decapsulating agent decapsulates the original datagram and so it can be delivered to the original destination address.

a logical entity

a logical interface on a Cisco router that provides a way to encapsulate passenger packets inside a transport protocol

a logical pathway thru the network

a logical structure that encapsulates the frame and data of one protocol inside the data field of another protocol

a method for sending datagrams between routers separated by gateways that do not support multicasting routing

a router where one interface uses a different protocol than the rest

The path established by one network to send its data via another network's connections; runs on OSI Layer 2 protocol such as TCP/IP, VPN and PPTP.

The logical path by which the encapsulated packets travel through the transit internetwork.

A path followed by a first packet while it is encapsulated within the payload portion of a second packet.

A very broad term which generally means that a data path has been created through a network, by encapsulating the original packets into some other protocol packets. Two popular examples for tunnelling are: hiding original packets (secure tunnels); providing a way of transferring non-supported packets, which are encapsulated within the network protocol packets, e.g. IP multicast through IP unicast-only network.

The path followed by a packet while it is encapsulated from the Home Agent to the mobile node. The model is that, while it is encapsulated, a packet is routed to a knowledgeable decapsulating agent, which decapsulates the datagram and then correctly delivers it to its ultimate destination.

Secure communication path between two peers, such as two routers.

In the context of this document, a tunnel refers to a secure communication path between two peers, such as two PIX Firewall units. It does not refer to using IPSec in tunnel mode.

A secure communication path between two peers, such as a client and a router.

The link between tunnel client and tunnel server where data is encrypted and encapsulated.

A secure communication path between two peers, such as routers.

A secured, private "path" connecting two points through a public network

A logical connection over which data is encapsulated. Typically, both encapsulation and encryption are performed and the tunnel is a private, secure link between a remote user or host and a private network. See also: encryption; host; tunnel server; voluntary tunnel

A virtual, direct pathway with which to transmit bidirectional traffic between two end points. See also VPN.

vb. To encapsulate or wrap a packet or a message from one protocol in the packet for another. The wrapped packet is then transmitted over a network via the protocol of the wrapper. This method of packet transmission is used to avoid protocol restrictions. See also communications protocol, packet (definition 2).

In Virtual Private Networks ( VPN), an encrypted connection between sites. Only the originator and the receiver of the message see it in its clear state. Any hacker trying to intercept the message en route gets nothing but a scrambled mess. Because the path of a VPN message has "light" (clear text) at each end but "darkness" (obscurity) at all the between-points, it is called, metaphorically, a VPN tunnel. On a technical level, a tunnel is a means of exchanging encapsulated data packets between two parties. Though some tunneling protocols forward cleartext packets, WatchGuard utilizes tunneling protocols such as PPTP and IPSec ESP that forward encrypted packets.

Private, secure path through an otherwise public network.

Tunnel is an often misused term. In one sense it can be used to refer to the Raptor Firewall's packet filtering ability - that is, local tunnels. It can also be used when discussing the implementation of VPN, as in RaptorMobile tunnels, IPSEC tunnels, or ISAKMP tunnels.

A level passage driven across the measures, or at right angles to veins which it is desired to reach; -- distinguished from the drift, or gangway, which is led along the vein when reached by the tunnel.

To form into a tunnel, or funnel, or to form like a tunnel; as, to tunnel fibrous plants into nests.

To make an opening, or a passageway, through or under; as, to tunnel a mountain; to tunnel a river.

To make a tunnel; as, to tunnel under a river.

A fairly level underground passage open to the surface at both ends.

a passageway constructed to allow trains to travel through mountains or under water.

An underground conduit, often deep and expensive to construct, which provides conveyance and/or storage volumes for wastewater, often involving minimal surface disruption.

Similar to a shaft, but driven horizontally into a mountain side. It can also be driven horizontally from the bottom of a shaft, or from any location on the shaft that the foreman decides upon. It is also known as a “drift”.

a large, underground structure used to store and transport wastewater, combined sewage or storm water during rain storms. Tunnels usually have higher storage capacities than basins and are capable of transporting their flows directly to a wastewater treatment plant.

Specifically, a tunnel is a cavity with a long horizontal or nearly-horizontal dimension and short dimensions at right angles to this long dimension that has an opening or portal at each end. More generally, a tunnel is the generalization of  addit, drift and tunnel.

a passageway through or under something, usually underground (especially one for trains or cars); "the tunnel reduced congestion at that intersection"

an underground or underwater passage that is primarily horizontal

a passage through a mountain or under a waterway , road or railroad

An underground road or passage

A nuclear device exploded at the end of a long horizontal drift mined into a mountain or mesa in a way that places the burst point deep within the earth.

An underground passage for vehicles or pedestrians, especially one which is created by digging into earth. Occasionally, tunnel structures are built in an excavated area then covered over.

An underground passageway, esp. one for trains or cars. Any passage through or under something.

An artificial underground passage built though a hill, through which track is laid allowing trains to pass.

Subterranean passageway created artificially to allow for communication from one place to another. Construction which comprises a long cylindrical cavity.

A horizontal, or near-horizontal, underground passage, entry, or haulageway, that is open to the surface at both ends. A tunnel (as opposed to an adit) must pass completely through a hill or mountain. Return to TERMS MENU

linear underground passageway open at both ends.

The underground passageway used by Metrorail cars.

An underground passage open to daylight at both ends.

a tunnel used to carry a roadway through a mountain or under a river instead of around or over those obstacles. Tunnels can be very expensive to construct and maintain due to drilling and ventilation requirements. Generally, most tunnels are located in mountainous or hilly regions, and examples include the Fort Pitt Tunnel (Interstate 279) in Pittsburgh and the Waldo Tunnel (U.S. 101) north of San Francisco.

A horizontal passageway through or under an obstruction; also called Wolfram. 2. Tungsten Steel.

A tunnel is an underground passage. The definition of what constitutes a tunnel is not universally agreed upon. However, in general tunnels have a ratio of the length of the passage to the width of at least 2 to 1.

a hole dug on different depths and sizes using different kinds of tools

Term used to describe a type of sealing head in which the cap travels through a tunnel that directs the induction sealing field to the induction liner.

The channel formed by the bottom of the main hull and the inner walls of a sponson.

Connecting two communication partners via a point-to-point connection.

A secure encrypted connection between two points through a public or third-party network.