Oracle cloud instance cannot communicate with each other via private ip within the same VCN subnet

I am really curious why this happen: Oracle cloud instances cannot communicate by default with each other via private ip within the same VCN subnet. Is it against intuition as in most cloud providers it is not the case. By now I didn't find any good or easy way except using Public IP. Can anyone give me a solution?

Emmm my bad. It turns out I need to open ICMP type 8 in security list. BY Default other icmp types are allowed:

https://docs.public.oneportal.content.oci.oraclecloud.com/en-us/iaas/compute-cloud-at-customer/topics/network/security-rules.htm#:~:text=There%20is%20no%20default%20rule,0.0%2F0%20for%20the%20source.