Hi,
dynamic vpn has been removed from Junos 15.1X49 and onwards. This means that it won't work on vSRXtogether with SRX300 series and SRX1500 appliances. If you need dynamic vpn, you have to stick with 12.1X or 12.3X releases.
The same situation also applies to policy-based VPN.
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Best regards,
Jonas Hauge