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GRE flapping -- three vendors pointing fingers

Hello --

Cisco interior router trying to maintain a GRE tunnel with regional zScaler cloud through a checkpoint R80.20-based cluster (latest GA HFA applied).

The GRE tunnel is flapping sporadically and everyone pointing fingers at each other.

CP TAC involved and simply did a "fw montor ..." traffic capture of proto 47 (GRE) to assert "we're passing the traffic".

However, the devil is in the details and wondering if anyone else encountered such an issue and have recommendations?


update #1:     if GRE keepalives are turned OFF on Cisco router, the GRE tunnel stays up.

ideally, we would like to do "fw monitor ..." specifically for GRE keepalives and validate NAT being properly applied on CP cluster.  This is current area of focus.


How GRE Keepalives works HERE.


Thanks -GA


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