Inject a fault: pull a link down
Testing how a network reacts to failure is half of network engineering. netplex. lets you pull a link down on a running lab - a real cable-pull on the wire - so you can watch routing reconverge, a failover kick in, or an alarm fire. Restore it just as easily.
The link between PC1 and PC2 is up and carrying traffic. Right-click it - the popover has the link tools, including fault injection.
Pull the link down. netplex. takes the real interfaces down on the wire - and a ping across it now fails, exactly as a cut cable would. Your routing protocols see the failure and react.
Restoring is the reverse - bring the link back up and traffic flows again. Fault injection pairs naturally with a packet capture (watch the failure and recovery on the wire) and with QoS (degrade a link instead of cutting it). It is how you prove a design survives failure, not just that it works when everything is perfect.