The Juniper SRX as it comes forwards IP traffic based on flows between security zones. It can be configured to forward traffic based on packets (no fancy security features). In packet mode an SRX acts just like a router or layer 3 switch. This is useful for labs and learning.
Run the following command to get an idea of how your SRX is forwarding traffic.
> show security flow status
By default Inet (IPv4) traffic is the only traffic that is configured to forward traffic in flow mode.
To disable this simply delete all of the configuration under the security hierarchy.
# delete security
# run request system reboot
To enable other traffic types use the following commands
# set security fowarding-options family inet6 mode packet-based
# set security fowarding-options family mpls mode packet-based
# set security fowarding-options family iso mode packet-based
You must now commit the configuration and reboot the device.
There is another method to do this that allows you to use both flow and packet mode on the same family which requires firewall rule. I will go over that in another post.