This article describes the issue of EX3200 and EX4200 rebooting with VMcore on Junos 9.5 and below.

A software bug exists, PR 439571 , with the EX3200 and EX4200 series switches, where the system could crash and cause a reboot. This is due to improper programming of certain MAC addresses beginning with an 'e' into the packet forwarding engine (PFE), which can cause a kernel panic and leads to a reboot of the system.

It is recommended, if this issue is being experienced, to upgrade to the latest recommended release. For more information, see KB21476 - JTAC Recommended Junos Software Versions.
[juniper.net]
Junos 9.5 and earlier is currently out of engineering support and is end-of-life. For further details regarding software milestones, see http://www.juniper.net/support/eol/junos.html .

Note : This issue has been resolved in Junos versions 9.5R2 and above.