Description

This article describes the issue of the OSPF neighbor being stuck in the Loading state.

Symptoms

To provide a possible workaround to a situation, in which the OSPF neighbor state is stuck in the Loading state.

Solution

OSPF has the following states:

  • Down
  • Attempt
  • Init
  • 2-Way
  • Exstart
  • Exchange
  • Loading
  • Full

This issue is related to the Loading state.

What is the Loading state?

"In this state, the actual exchange of link state information occurs.
Based on the information provided by the DBDs, routers send link-state request packets.
The neighbor then provides the requested link-state information in link-state update packets.
During the adjacency establishment, if a router receives an outdated or missing LSA, it requests that LSA by sending a link-state request packet.
All link-state update packets are acknowledged."
 
  • In a Hub-and-Spoke scenario, if the hub site has a larger MTU configured on the external interface defined in ike gateway and the size of the link state database is large, then the neighbor state could get stuck in the Loading state.
  • Due to the large size of the link state database, the hub will send out larger packets; which will get dropped at the spoke and the database will never synchronize.

Workaround :
Look for any MTU mismatches in the whole path of OSPF, especially on the hub, which is primarily responsible for sending large link state database packets. If there is any mismatch, remove that configuration.