In one direction APIC-EM can discover path of the flow and in another it can't. Problem is always in the same interface of the switch. What could be wrong with the configuration of the switch or path trace.
while return path trace its taken as unknown device Please find page 19 of this url- http://www.cisco.com/assets/global/DK/seminarer/pdfs/cisco_tech_update_apic-em_sdn_18_og_20_august_2015.pdf
After resetting APIC-EM and discovery of all devices it shows only this error every time:
"Unable to construct path: 7ad10f68-159a-40a7-818a-d5b5d058ada9 : Topology information changed during Path Calculation. Path link is missing in topology"
checked CDP and SNMP read and it is all enabled.
Do you see the "Managed" status on all the network devices in the inventory. If you see partial collection failure then some of the links may not have been discovered by APIC-EM.
Tried to make topology that would be compliant with IWAN app design. Tried to simulate LAN network in the Hub site over the switch that didn't work because layer 2 switch was between two layer 3 routers and path trace didn't work with that topology. Also tried to simulate the provider's VPNs with hubs. but didn't had enough hubs to separate them, so routers had overlapping paths between them that confused path trace.
In the end simplified network topology as in the following picture. We connected only one branch router on each hub router and now path trace works.