| Description | This article describes how to monitor GRE tunnel using keepalive. |
| Scope | FortiGate, GRE Tunnel, GRE over IPsec. |
| Solution |
The GRE tunnel interface will always be 'up'. This means that the same route will still be used even when the remote GRE tunnel is down. To work around this, configuring keepalive or a link monitor is recommended.
For link monitor configuration: Technical Tip: GRE Tunnel monitoring
By default, GRE keepalive is set to '0' on FortiGate, which means that keepalive is disabled:
After setting the desired 'keepalive-interval', keepalive will be running and start monitoring the tunnel. If no value is set for 'keepalive-failtimes', FortiGate will use '10' which is the default value:
With the keepalive properly configured and matching on local and remote ends, run 'diagnose sys gre keepalive' to monitor it:
When the keepalive fails according to the 'interval' and 'fail' timers, the routes via the GRE tunnel will be removed from the routing table.
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