Preventing Recursive Tunnels

If routing information about the tunnel network combines with routing information about the transport networks (the networks that the tunnel services), a recursive tunnel can occur. In this case, the routing table defines the tunnel itself as the best path to a tunnel destination. To prevent recursive tunnels, differentiate routing information for the tunnel network and the transport networks with one or both of the following techniques:

• Use different routing protocols for the tunnel network and the transport networks.
• Define a static route to the tunnel destination.

  Note: If you define a static route to a tunnel destination, be careful not to create routing loops.

Figure 20 illustrates how to prevent recursive tunnels by using different routing protocols for the tunnel network and the transport networks.

Figure 20: Transport and Tunnel Networks Using Different Routing Protocols

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