Chapter 2 Advanced Routing for FortiOS 5.0 : Intermediate System to Intermediate System Protocol (IS-IS) : Troubleshooting IS-IS
  
Troubleshooting IS-IS
If you want to troubleshoot Integrated IS-IS, it is the same as with IS-IS but you must specify the different protocol, and use IPv6 addresses. This applies to commands such as get router info6 when you want to see the routing table, or other related information.
This section includes:
Routing loops
Split horizon and Poison reverse updates