Hello Biplob,
The traffic is allowed inside a VPN tunnel (TCP / ICMP etc) , depending on the Crypto ACL defined on the devices.. incase someone gives ACL permit tcp etc etc, it will not allow ICMP... normally people give the ACL to allow IP access between the source and destination networks, in which case the ICMP will work..
If you have given IP access, and even then there is an issue with reachability, after the IPSEC tunnel comes up, i think it could be a problem with routing or NAT !! Make sure the source and destination ip addresses are reachable from all the devices doing VPN...
Hope this helps.. all the best..
Raj