ACI - Can't reach hosts outside the fabric until traffic is inititated from an outside host into a fabric-connected host

[bascheew]

I have a group of ports statically mapped to the same EPG and VLAN on my ACI fabric.  One of the ports connects to an uplink port on a 3750x stack.  From the hosts on the fabric, I cannot ping hosts on the 3750 until I initiate traffic from the hosts on the 3750 in to the fabric.  Once that's done on each 3750 host they can all talk to each other.  Why is this happening?

Thanks!

[Joseph Ristaino · Accepted solution]

When the traffic is failing, the destination is likely not learnt as an EP in the fabric.  You can verify this by looking at the operational tab of the EPG.

Once you ping from the 3750, we learn the EP and traffic works from the original source.  When the BD is in "Hardware Proxy" mode, the destination needs to be learnt.

 If you change the BD mode to "Flood", then we will flood and learn like a normal switch.

Joey