Core Issue
If the tunnel interface learns that the best path to the tunnel destination is through the tunnel itself, the interface shuts down temporarily.
A recursive routing error occur when router does route look up for Prefix A points at prefix B and a lookup for prefix B points at prefix A.This problem can be easily identify by IOS message "%TUN-5-RECURDOWN: Tunnel0 temporarily disabled".Another symptom of this problem is continuously flapping of EIGRP,OSPF,or BGP neighbors, when the neighbors are over a GRE tunnel.
Resolution
To avoid recursive routing problems, keep passenger and transport network routing information disjointed with one of these methods:
->Use a different Autonomous System (AS) number or tag.
->Use a different routing protocol.
->Use static routes to override the first hop, but watch for routing loops. For more information, refer to the Special Considerations section of Configuring Logical Interfaces.
To further address this issue, and for more information about special configurations and precautions for configuring tunnels, refer to Troubleshooting the "%TUN-5-RECURDOWN" Error Message and Flapping EIGRP/OSPF/BGP Neighbors Over a GRE Tunnel.
Related Information
Base Initial configuration:
GRE - Recursive loops
GRE overview and troubleshooting.
