From the VPN interface on Router PE1 (VPN1), ping the loopback interface, 10.255.10.4, on Router CE1:
user@vpn1> ping 10.255.10.4 interface
fe-1/1/0.0 local 192.168.192.1 count 3
PING 10.255.10.4 (10.255.10.4): 56 data bytes 64 bytes from 10.255.10.4: icmp_seq=0 ttl=255 time=0.838 ms 64 bytes from 10.255.10.4: icmp_seq=1 ttl=255 time=0.760 ms 64 bytes from 10.255.10.4: icmp_seq=2 ttl=255 time=0.771 ms --- 10.255.10.4 ping statistics --- 3 packets transmitted, 3 packets received, 0% packet loss round-trip min/avg/max/stddev = 0.760/0.790/0.838/0.034 ms