> Source: [sk184516](https://support.checkpoint.com/results/sk/sk184516)

# sk184516 - IS-IS Messages, Common Issues, and Troubleshooting 

| Property | Value |
|----------|-------|
| Solution ID | sk184516 |
| Date Created | 2026-01-07 |
| Last Modified | 2026-01-08 |
| Technical Level | Advanced |
| Products | Security Gateway, Scalable Platforms |
| Versions | R82.10, R82, R81.20, R81.10 (EOS), R82.10, R82, R81.20, R81.10 (EOS) |
| OS | Gaia |
| Platform | 15000, 3000, 28000, 44000, 64000, 16000, 26000, Maestro Orchestrator, 19000, 29000 |

## Symptoms

- * Intermediate System to Intermediate System (IS-IS) neighbors do not form or remain stuck in the "Initializing" state.

* Routing tables are incomplete or inconsistent, with expected routes missing.

* IS-IS adjacencies form and then drop intermittently.

* Logs show IS-IS authentication failures.

## Cause

One or more of the following conditions may prevent proper IS-IS operation:

* Mismatched network types or authentication settings
* Maximum Transmission Unit (MTU) mismatches on IS-IS interfaces
* Layer 2 connectivity issues
* Hello interval mismatches
* LSPs not exchanged due to Complete Sequence Number Protocol Data Unit (CSNP) / Partial Sequence Number Protocol Data Unit (PSNP) packet loss
* Database desynchronization between routers
* Authentication key mismatch
* Area address mismatch
* Incorrect interface configuration

## Solution

This solution requires authentication. Please log in to view the full solution.

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