As part of the basic design ACE does not send traffic to IP's, but to encapsulation "targets".
You can see this with the "show ip fib" command:
cdn-ace-1/pevaneyn# show ip fib
FIB for Context pevaneyn (RouteId 16)
Codes: H - host, I - interface
S - static, N - nat
A - need arp resolve, E - ecmp
Destination Interface EncapId Flags
------------------------------------------------------------------------
...
192.168.10.1/32 vlan499 69 H [0x3]
This EncapId (here 69) is then used to send commands to the server, but also to classify traffic coming from that IP. We can check this by:
cdn-ace-1/pevaneyn# show arp | i 192.168.10.1
192.168.10.1 00.19.aa.1a.36.1b vlan499 LEARNED 69 4834 sec up
...
cdn-ace-1/pevaneyn# show np 1 adjacency 69 69
id S:Ver flag imph 1 imph 2 DstMac SrcMac MTU ifid
--------------------------------------------------------------------------------
69 1:0 1 1f3 0 0019:aa1a:361b 000b:fcfe:1b7e 1500 76
As you can see the adjacency uses the MAC address. If you want to send traffic from a different MAC you need to first send a gratuitous ARP.
All of this means that if you send traffic from the correct IP but with the wrong MAC the ACE will just drop the packet. So if you are using a teaming server which sends traffic with a different MAC on failover or when the load is high enough this will cause problems.
See for example documentation bugs CSCtt33758 or CSCth66757.
If at all posible configure and use a port-channel with a unique, non-changing, MAC address.
