| 6.1 |  | Virtual Private Networks |
| 6.1.5 |  | Tunnel interfaces |

| Tunnel interfaces provide a point-to-point connection between two routers through a virtual software interface. They also appear as one direct link between routers hiding the underlying infrastructure that are connected via a large network, such as the Internet. However, tunnel interfaces should not to be confused with IPSec or L2TP tunnels, which can act as tunnels but not as true Cisco IOS interfaces.

Further tunnel interface configuration information that may prove important is as follows:

- Unnumbered Layer 3 addresses are supported but not allowed for by IPSec.
- Access-lists can be applied to the tunnel interface.
- QoS supports traffic requiring consistent service such as voice over IP.
- Committed Access Rate (CAR), Weighted Fair-Queue (WFQ), and Weighted Random Early Detection (WRED) are not supported on tunnel interfaces at this time.

GRE
Generic Routing Encapsulation (GRE) tunnels provide a designated pathway across the shared Wide Area Network (WAN) and encapsulate traffic with new packet headers, which ensures delivery to specific destinations . The network is private because traffic can enter a tunnel only at an endpoint. Tunnels do not provide true confidentiality as encryption does, but can carry encrypted traffic. IPSec can be used to encrypt data before it enters as well as after it leaves the GRE tunnel.

| Web Links GRE http://www.cisco.com/en/US /tech/tk827/tk369/tk287/ tech_protocol_home.html