I have multiple Amazon EC2 instances which need to communicate using private IPs. However, so far I've been unable to ping one instance's private IP from another instance.
I can ping external addresses, such as their Elastic IPs and other sites (yahoo, google, etc), so it seems there's nothing wrong with the instances' network configuration.
Also, they are all in the same zone, so that shouldn't be an issue.
Does anyone have any idea what I could be doing wrong? Could this related to the Security Group settings?