Creating a network lab in GNS3 is reliefs on budget. But there are some drawbacks. One of which is port status. I have noticed that using GNS3 in combination with iouyap results in some unexpected behavior.

Once a topology is made in GNS3. And one interface is set administrative operational, with no shut. The port immediately becomes operational i.e. up/up. Within GNS3 there is no such thing as admin up/operational down.

At this point I know that two protocols can help detect L2 communication with adjacent node. Those are UDLD and BDF.

Beware not to waste time in resolving/troubleshooting GNS3 problem. Instead of resolving network problems.