Hello,
I have not had this problem in the past, and I have burned up a lot of time trying to troubleshoot this.

A couple of times, I have gotten everything working, but it fails again.

In this lab, i have a chain of 3750's, acting as switches (trunking for labs) -- but also L3 between the devices.

1. I never have a problem seeing the adjacent swrouters using CDP.
2. ....but I cannot ping the IP addresses of the directly connected interfaces.

As a result, the OSPF routing protocol fails.

If I cannot get this fixed, I am going to have to go to a rental lab (ccie).

Any ideas? Thanks.

Just now I was able to get everything up, by shutting down both sides of interfaces and then bringing them back up. I will update how long this lasts.

Is there a trick with the 3750's (in GNS3) to keep the interfaces pingable? I have not experienced this issue before with any of my labs.

I'm having the same problem and came across this post!

GNS3 (0.8.6) will show CDP information when connected to a 3750 but is unreachable via ping, Wireshark capture states unknown host.

If I swap out the 3750 for a 2960, works a treat! I've tried the 3750 connection as a routed port and an access interface without result :(

Wonder if any of you guys could shed light on this?

Using Windows 8.1 x64 with Intel Quad PT NIC, Intel CT NIC and USB 2.0 AX88772 based device - same result.

I've disabled IPv4 and IPv6 on the Windows stack and re-enabled various combinations without success.

VMWare Workstation has full reachability through all NICs in bridge mode.

Thanks in advance...