OCI: Instance Without Networking Is Unable to Ping Subnet Gateway

Applies to: 

Oracle Cloud Infrastructure - Version N/A and later

Linux x86-64

 

Symptoms

OCI Compute OL7 instance suddenly unreachable.

When accessing from serial console it can be seen that DNS does not resolve hostnames and the subnet gateway is not pingable with the messages:

 $ ping 10.x.x.1
 PING 10.x.x.1 (10.x.x.1) 56(84) bytes of data.
 ping: sendmsg: Operation not permitted
 ping: sendmsg: Operation not permitted
 ping: sendmsg: Operation not permitted

This could be an indication that a firewall is blocking network traffic.

But in this case, firewalld is disabled and iptables is allowing all traffic:

 $ iptables -L
 Chain INPUT (policy ACCEPT)
 target    prot opt source              destination        
 
 Chain FORWARD (policy ACCEPT)
 target    prot opt source              destination        
 
 Chain OUTPUT (policy ACCEPT)
 target    prot opt source              destination