Troubleshooting EIGRP & OSPF (Some typical problems)

EIGRP 1. Troubleshooting EIGRP Neighbor Relationships 1. Unidirectional link 2. Uncommon subnet, primary, and secondary address mismatch 3. Mismatched masks 2. Troubleshooting EIGRP Route Installation 1. Duplicate router IDs 3. The "%TUN − 5 − RECURDOWN" Error and Flapping EIGRP/OSPF/BGP Neighbors Over a GRE Tunnel

General Flowchart on Troubleshooting EIGRP Neighbor Relationships

1.1.EIGRP Neighbor Problem—Cause: Unidirectional Link The SRTT timer is 0 indicates that no acknowledge-ment packets are being received

1.1.EIGRP Neighbor Problem—Cause: Unidirectional Link The Q count is not decrementing, which indicates that the router is trying to send EIGRP packets but no acknowledgement is being received

1.2.EIGRP Neighbor Problem—Cause: Uncommon Subnet

1.3. EIGRP Neighbor Problem—Cause: Mismatched Masks ROUTING LOOP UPDAT E ACK,DA(.1.1)

1.3. EIGRP Neighbor Problem—Cause: Mismatched Masks RETRY LIMIT EXCEEDED 16 RETRIEs

2.1. EIGRP Is Not Installing Routes— Cause: Duplicate Router IDs EIGRP uses the notion of router ID only on external routes to prevent loops R1#show ip eigrp topology

3. The "%TUN−5−RECURDOWN" Error and Flapping EIGRP/OSPF/BGP Neighbors Over a GRE Tunnel %TUN-5-RECURDOWN: Tunnel0 temporarily disabled due to recursive routing

3. The "%TUN−5−RECURDOWN" Error and Flapping EIGRP/OSPF/BGP Neighbors Over a GRE Tunnel

1.The packet is queued in the output queue of the tunnel interface. 2.The tunnel interface adds a GRE header to the packet and queues the packet to the transport protocol destined to the destination address of the tunnel interface. 3.IP looks up the route to the destination address and learns that it is through the tunnel interface, which returns the packet to Step 1 above; hence, there is a recursive routing loop.

OSPF 1. OSPF Not Installing Any Routes in the Routing Table 1. The network type is mismatched 2. The Effects of the Forwarding Address on Type 5 LSA Path Selection

1.1. OSPF Not Installing Any Routes in the Routing Table—Cause: Network Type Mismatch BROADCASTPOINT-TO- POINT Hello 10, Dead 40 R2R3

1.1. OSPF Not Installing Any Routes in the Routing Table—Cause: Network Type Mismatch

2. The Effects of the Forwarding Address on Type 5 LSA Path Selection

Reference  Troubleshooting IP Routing Protocols (CCIE® Professional Development) 