Sflow EX4200 problem with gre traffic

Sflow EX4200 problem with gre traffic

hi 
i am trying to monitor a site to site link from a juniper ex4200 device 
but there is a gre tunnel  betwenn both core switches in both  sites
and when i monitor the physical interface in the juniper  it shows all traffic 
but encapsulated GRE_ APP
and i am not able to see any conversation on the link 
the link is congested and i need to monitor the sessiion between both sites 
so any solution for this gre traffic ?

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