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GAIA: tcpdump filtering with GRE ?

Question asked by Javier Gurfinkiel on Aug 13, 2018
Latest reply on Aug 17, 2018 by Dameon Welch-Abernathy


I'm trying to come up with the proper syntax to filter a specific IP which is encapsulated within a GRE tunnel. Googling around this seems to be a unique topic, and this the closest I could find:

No valid hosts found - the blog about openstack: How to filter IP addresses inside GRE in tcpdump 


...but I'm having trouble on GAIA: the command is being accepted, but it's filtering zero packets even though I know the traffic is there and passing through the gateway. I suppose the syntax for for the target IP may need to be expressed differently, but it's just a theory at this time. Also thought of using fw monitor for this purpose, but the syntax is even more complicated, at least for my limited scripting abilities.


Any help will be much appreciated!