It sounds like your Cisco router 3945 may be experiencing an issue where the internet connection fails to initialize properly after a reboot or power outage. This could be due to a configuration problem, interface flapping, routing or NAT issues, or even hardware malfunctions. By performing a shutdown and then a no shutdown on the affected interface, you're essentially resetting the connection and allowing it to reestablish properly. To address this issue, you should check for misconfigurations in the router's configuration file, verify the physical connection, review router logs for errors, test internet connectivity using diagnostic commands, and consider contacting your ISP for assistance. If the problem persists, further troubleshooting or consultation with Cisco technical support may be necessary to resolve the issue and ensure reliable internet connectivity.
