I have configured varnish cache at STORES > Configuration > ADVANCED > System > Full Page Cache. and to export a Varnish configuration file from the Admin panel. but I could not start varnish after I replaced existing default.vcl with the one I just exported.
my varnish version is 3.0.7, so I exported vcl for varnish 3.
Which error are you getting when you try to start Varnish?