The ping command is a pervasive troubleshooting tool used by network administrators and engineers. One important, but sometimes overlooked, detail is the source that is used by the traffic it creates. By default ping uses the IP address of the outgoing interface as the source of ICMP Echo messages. When this command is issued from a router with multiple interfaces, a positive response may not necessarily confirm the expected connectivity between two networks.
The video below outlines the scenario in detail and demonstrates why it is sometime important to specify the source when attempting to validate connectivity.