Simulation Mode: Special Notes

Editing the Network and Using the Cisco IOS in Simulation Mode

Although Realtime Mode is the preferred mode for network configuration, you can also edit the network directly in Simulation Mode. You have full access to the Common Tools Bar and the Network Component Box. You also retain access to the Cisco IOS (or in the case of the PC, the command prompt). When you work with the IOS in Simulation Mode, the network responds to most of your command sequences in realtime. For example, when you issue the shutdown command on a port, that port will go down immediately. Any command that does not involve the propagation of PDUs in the network will have a realtime response. Command sequences that do cause or affect the propagation of PDUs will require the user to click the Auto Capture / Play or Capture / Forward button in order to see the results. For example, after you issue the ping command sequence from the IOS on a router, the appropriate PDU animation icons will appear on the workspace (as if you had used the Add Simple PDU button), but you would need to click the Auto Capture / Play or Capture / Forward button to watch the PDUs propagate. The IOS status messages or indicators will synchronize with the events of the simulation and play speed, appearing to be very slow. Note that packets created by IOS commands do not appear on the User Created PDU List.

Time Management Between Realtime and Simulation Mode

Realtime Mode and Simulation Mode share a common "master" timeline. The master timeline is transparent to the user; you cannot "see" it in numerical form. The master timeline only moves forward; you cannot "reset" it or move backwards in time. The master timeline is always advancing when you are in Realtime Mode (moving at the modeled speed of realtime as shown in the Realtime/Simulation Bar). When you switch to Simulation Mode, the master timeline pauses and falls somewhat under your control. At that point, you will be running under simulation time, which can be thought of as a "segment" of the master timeline. You can use the Auto Capture / Play or Capture / Forward buttons to move forward in simulation time, which will cause the master timeline to advance accordingly. You can use the Back button to view a previous network state; however, time does not actually "travel backward". The master timeline will remain at its "most-forward" state. For example, if Event A occurs, and then you use the Back button to move back in time to create Event B, the result will not be what you would expect. When you play this scenario, Event B will take place after Event A, even if you think you have "forced" Event B to occur first. Thus, it is impossible to interfere or pre-empt an event that already has occurred, and you should not consider using the Back button for that purpose. If you clear the event list, the simulation time will restart at 0.000, but the master time will continue from the last event.

When you switch back to Realtime Mode, the master timeline will continue off of the last event in Simulation Mode and move forward at realtime speed again. If you started some event in Simulation Mode, and then switch to Realtime Mode, that event will continue and finish in realtime. For example, if you created a ping between two devices in Simulation Mode and then you switch to Realtime Mode, that ping will proceed (even if you have not pressed the Auto Capture / Play or Capture / Forward button back in Simulation Mode). One of the powerful features of Packet Tracer is the ability to manipulate time and events on the model network; however, be aware that interpreting intermediate results, like viewing switching and routing tables while network protocols are still converging, can be a complex task.