> Source: [sk109092](https://support.checkpoint.com/results/sk/sk109092)

# sk109092 - OSPF with enabled MD5 authentication is not establishing adjacency due to MTU mismatch

| Property | Value |
|----------|-------|
| Solution ID | sk109092 |
| Date Created | 2015-12-12 |
| Last Modified | 2017-05-21 |
| Technical Level | Advanced |
| Products | Security Gateway |
| Versions | R82.10, R82, R81.20 |
| OS | Gaia |

## Symptoms

- OSPF with enabled MD5 authentication is not establishing adjacency.

## Cause

When MD5 authentication is enabled, OSPF subtracts 16 bytes from the MTU it advertises. This is causing the OSPF neighbor (e.g., Cisco router) not to establish adjacency.

## Solution

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

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