One of the most powerful features of Packet Tracer is the Simulation Mode. Whether you are looking to study packets in detail, or troubleshoot why a connection does not work, Simulation mode will get you the answers.
How to switch to simulation mode:
Click on the stopwatch icon in the bottom right on the yellow bar. This will toggle you between simulation mode and realtime mode.
Note: Simulation mode is not available when connected to a multiuser connection. However, you may save your file and the remote user's network file (up to a certain depth if necessary) to a local file and look at simulation mode from that file.
In Simulation Mode, there is a new dock window containing the Event List and Play Controls. Use the Play Controls to forward one discrete time period and see packets moving. If you do no see the expected packet, click the Event Filters to ensure the desired packet is being displayed.
Clicking on the packets in the workspace will open the packet for detailed inspection. Double clicking on the packet in the Event List will also open it for detailed inspection.
To use simulation mode for troubleshooting, ensure your packets are visible first. Then use the play controls to advance the time to see your packet moving across the network. Packets with a green Check on it is an accepted packet at the device. Packets with a red X is one that has been dropped. Packets may also have a Queued animated symbol as well. If a packet is expected to go to a certain destination but you are not seeing this behavior, look to see where the packet is being dropped. Click on the packet, and click through the OSI layers, reading the description for why it may be dropped. This will give you a clue as to what configuration is incorrect.