cisco ccna full course

cisco ccna full course.Figure 24.8 Example of a GRE tunnel24.5.1 GRE OverviewCisco ios uses a logical tunnel interface to provide a logical connection between devices. When "tunneling" a packet, additional information is added to the original data (packet or frame) indicating that GRE is being used and to which destination GRE device it is to be forwarded. Figure 24.9 illustrates the encapsulation process. The added GRE header is 24 bytes long, which does not include the length of the external IP header. Cisco supports encapsulation of Layer 3 packets (such as IPv4, IPv6, IPX, and so on) or Layer 2 frames (bridged traffic).For example, in Figure 24.8, the subnet 192.168.1.0/24 provides logical connectivity. On networks 172.16.0.0/16 and 172.17.0.0/16, the Internet appears as if it were a logical hop that connects them. When IP packets are transmitted between these two networks, they are encapsulated using GRE. For example, when a packet from 172.16.1.1 to 172.17.1.1 arrives at Router A, the router adds a GRE header and then an IP header with the source address of Router A (200.200.200.1) and the destination address of Router B (201.201.201.1). o This allows Router A and Router B to transport traffic between these two networks through a tunnel.Figure 24.9 GRE encapsulation processGRE has the following characteristics: . . it can carry any Layer 3 protocol and bridge traffic; . It is stateless and does not provide any traffic control or acknowledgement mechanisms; .. Does not provide any security mechanisms (but can be protected using solutions such as IPSec - which is out of the scope of this book) o24.5.2 Configuration and validation of GRETo implement a GRE solution, the following needs to be done: . Create the tunnel interface .. Specify the GRE tunnel mode (optional); . Specifying the source and destination routers for the logical tunnel; .